Satellite-borne array laser radar three-dimensional topographic surveying and mapping data comprehensive analog simulation method and system

Abstract

The invention provides a satellite-borne array laser radar three-dimensional topographic surveying and mapping data comprehensive analog simulation method and system. The method comprises the following steps: establishing a satellite-borne array laser radar three-dimensional topographic surveying and mapping simulation link; constructing a satellite-borne array laser radar comprehensive analog simulation model, and generating a satellite-borne array laser radar three-dimensional terrain simulation data set; and evaluating the quality of the satellite-borne array laser radar three-dimensional topographic surveying and mapping analog simulation data under the condition of configuring different parameters by adopting a plurality of evaluation indexes such as noise rate, average signal photon number, detection probability, signal-to-noise ratio and elevation precision. The invention designs a satellite-borne array laser photon cloud data analog simulation method for ground laser angle reflection (CCR). A set of satellite-borne array laser radar three-dimensional terrain simulation data set is generated by taking a certain type of domestic satellite parameters as an example; a plurality of evaluation indexes are adopted to evaluate the quality of satellite-borne array laser analog simulation data under the condition of configuring different parameters, and a solid foundation is provided for developing array laser three-dimensional topographic mapping satellites.

Description

Technical Field

[0001] The present invention relates to the field of active remote sensing technology, and in particular to a method and system for comprehensive simulation of three-dimensional terrain mapping data using a satellite-borne array laser radar. Background Art

[0002] Since the 1970s, satellite laser altimetry (SLAL) has garnered significant international attention as an active remote sensing technology. Along with imaging spectroscopy and synthetic aperture radar, it is considered one of the three core technologies for Earth observation in the 21st century. The principle behind SLAL is to carry a laser altimeter on a satellite platform and transmit laser pulses to the ground at a constant frequency. By measuring the time difference between the laser pulse's transmission, reflection from the ground, and subsequent reception, the precise distance of the one-way transmission of the laser pulse is calculated. Combined with the precisely measured satellite orbit, attitude, and laser pointing angle, the three-dimensional coordinates and elevation distribution of the laser's ground footprint are ultimately determined.

[0003] The development trend of satellite laser altimetry is progressing from single-beam laser sparse point and multi-beam along-track two-dimensional profile measurement to array laser area continuous three-dimensional point cloud measurement. my country's Ziyuan-3 02 (ZY3-02), launched on May 30, 2016, successfully conducted the first test of a laser altimetry payload and mapping application. The Gaofen-7 satellite, launched on November 3, 2019, achieved operational operation of a two-beam full-waveform laser altimeter system, primarily used for obtaining elevation control points for global 1:10,000 scale stereo mapping. Ziyuan-3 03 (ZY3-03), launched on July 25, 2020, is equipped with a single-beam threshold detection laser altimeter system, enabling the acquisition of elevation control points for 1:50,000 scale stereo mapping. The Terrestrial Ecosystem Carbon Monitoring Satellite, equipped with a multi-beam lidar, was successfully launched on August 4, 2022, capable of along-track multi-beam laser measurement of sparse surface points. The foreign ICESat-2 was launched on September 15, 2018. It is the world's first laser altimeter satellite using photon counting technology. The advanced topographic laser altimeter system ATLAS equipped on it can realize 6-beam dense terrain profile measurement along the track, providing an important foundation for the future development of dense three-dimensional laser topography mapping satellites.

[0004] However, there are currently no LiDAR satellites capable of directly capturing 3D terrain. While optical stereo photogrammetry and radar interferometry can also be used for 3D terrain mapping, these methods suffer from limitations such as long data processing times, multi-view image occlusion, radar signal overlap with high mountains, and an inability to measure understory or underwater terrain. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to address the shortcomings of existing optical and radar satellites in effectively meeting the needs of polar glacier mapping, forest and understory terrain mapping, alpine mapping, and coastal mapping. A comprehensive simulation method and system for satellite-borne array lidar three-dimensional terrain mapping data is designed, a satellite-borne single-photon array laser altimeter simulation link is established, and a satellite-borne laser comprehensive simulation model including an array laser geometric positioning model, a radiation transmission model, and a single-photon detection model is constructed. A satellite-borne array laser photon cloud data simulation method for ground laser angular reflection CCR is designed. Taking the parameters of a domestic satellite as an example, a set of satellite-borne array laser simulation data sets is generated; and multiple evaluation indicators are used to evaluate the quality of satellite-borne array laser simulation data under different parameter conditions, providing a solid foundation for the development of array laser three-dimensional terrain mapping satellites.

[0006] The present invention provides a method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar, comprising the following steps:

[0007] S1. Establish a three-dimensional terrain mapping simulation link for spaceborne array lidar;

[0008] S2. Construct a comprehensive simulation model for three-dimensional terrain mapping by spaceborne array lidar and generate a three-dimensional terrain simulation dataset by spaceborne array lidar.

[0009] S3. Use multiple evaluation indicators such as noise rate, average signal photon number, detection probability, signal-to-noise ratio, and elevation accuracy to evaluate the quality of spaceborne array laser simulation data under different configuration parameters.

[0010] The method for constructing a satellite-borne laser comprehensive simulation model in step S2 includes the following steps:

[0011] S21. Construct a rigorous geometric positioning model for array lasers, including:

[0012] Perform relevant coordinate system definitions and conversions;

[0013] Based on the defined and transformed coordinate system, a rigorous geometric positioning model of the spaceborne array laser altimeter is established;

[0014] Specifically, before a satellite launch, application requirements analysis, technical specification design, product design, and key technology research are all required. Simulation analysis is an important way to support this work. Comprehensive simulation of satellite-borne laser data for high-precision 3D mapping is conducted. This involves studying conditions with varying footprint sizes, array densities, atmospheric conditions, lighting conditions, and terrain. The data characteristics of 3D imaging with satellite-borne array lasers are analyzed, and measurement accuracy and application feasibility are evaluated. This can provide in-depth guidance for overall satellite design, parameter optimization, and optimal operating mode selection.

[0015] As an active imaging altimeter, the spaceborne multi-beam array laser altimeter with GM-APD focal plane can locate the target mainly based on the distance ρ between the target and the satellite.

[0016] Traditional spaceborne laser altimeters determine the three-dimensional coordinates of a target by tracking the propagation path of the emitted laser light. However, for spaceborne array laser altimeters, the laser light emitted only illuminates the Earth's surface. The coordinates of each detector pixel corresponding to the target must be calculated. Therefore, spaceborne array laser altimeters must track the position of the corresponding LiDAR pixel to the corresponding ground target position to locate the target.

[0017] S22. Construct array laser radiation transmission model;

[0018] S23. Construct a single-photon detector response model.

[0019] Furthermore, the method for performing the relevant coordinate system definition and conversion in step S21 includes the following steps:

[0020] S211, establish array laser radar coordinate system (O L -X L Y L Z L ); take the lens center of the laser radar imaging system as the coordinate origin O L , the Z axis is perpendicular to the focal plane of the detector and points to the nadir direction, and the X axis and Y axis are parallel to the edge of the focal plane array and form a right-handed system with the Z axis;

[0021] In the laser radar, the detector array, lens, and each pixel are rigidly connected. The relative position of the detector array and lens and the spacing between pixels can be considered fixed. Assume that the distance between the optical center of the laser detector and the focal plane is , the coordinates of the array center in the laser radar coordinate system are expressed as (0, 0, - ), suppose the detector array has n rows and m columns, m, n are even numbers, and the pixel size is , taking the first pixel in the upper right corner of the detector array as the pixel in the first row and first column, the coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are expressed as:

[0022] ;

[0023] The coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are calculated to obtain formula (1):

[0024] (1)

[0025] The three-dimensional coordinates of the corresponding ground laser footprint points In the laser radar coordinate system, it is expressed as formula (2):

[0026] (2)

[0027] In formula (1) and (2), Obtain the distance value from the pixel position to the target for the lidar system; The projection is in X L O L Y L Plane and X L The angle between the positive directions of the axes; To point to Z L The angle between the positive directions of the axes;

[0028] S212, establish the satellite body coordinate system ( B -X B Y B Z B ); define the satellite body coordinate system as follows: the satellite mass center is the coordinate system origin O B , the X-axis points to the flight direction, the Z-axis points to the nadir, and the direction of the Y-axis is determined by the right-hand rule;

[0029] The LiDAR array coordinate system is not strictly parallel to the satellite coordinate system. There is an installation angle between the LiDAR array and the satellite. Therefore, coordinate translation and rotation transformations are required to convert the position of the ground point in the LiDAR array coordinate system to the satellite coordinate system:

[0030] (3)

[0031] In formula (3), is the coordinate of the ground point in the satellite coordinate system, is the rotation matrix of the array lidar transformed to the satellite body coordinate system, is the offset between the center of the array lidar lens and the origin of the satellite body coordinate system;

[0032] S213, establish orbital coordinate system (O O -X O Y O Z O ); The origin of the orbital coordinate system (which is the transitional coordinate system between the on-board and pixel coordinates) is the satellite's center of mass, the X-axis points in the direction of the satellite's flight, the Z-axis points to the center of the Earth, and the Y-axis is perpendicular to the XOZ plane and forms a right-handed system with the X-axis and Z-axis;

[0033] The coordinate centers of the satellite body coordinate system and the orbital coordinate system are consistent. Only three-axis rotation is required to complete the coordinate transformation from the satellite body coordinate system to the orbital coordinate system:

[0034] (4)

[0035] In formula (4), is the coordinate of the ground point in the orbital coordinate system; is the rotation matrix for transforming the satellite body coordinate system to the orbit coordinate system, The three attitude angles of the satellite determined by the star sensor: roll angle , pitch angle , yaw angle composition:

[0036] (5)

[0037] S214. Establish a space-fixed inertial reference frame (International Celestial Reference Frame, ICR). Use the Earth's center of mass as the coordinate origin, the X-axis pointing to the vernal equinox, the Z-axis pointing to the celestial north pole, and the Y-axis perpendicular to the XOZ plane, forming a right-handed reference frame with the X and Z axes. The J2000 coordinate system is typically used.

[0038] The orbital coordinate system is transformed into the ICRF coordinate system by coordinate translation and rotation:

[0039] (6)

[0040] In formula (6), is the offset between the origin of the orbital coordinate system and the origin of the ICRF coordinate system in the ICRF coordinate system. To solve the rotation matrix from the orbital coordinate system to the ICRF coordinate system, it is necessary to know the position vector of the satellite in the ICRF coordinate system at time t. and the velocity vector , the calculation expression of the rotation matrix between the orbital coordinate system and the ICRF coordinate system is:

[0041] (7)

[0042] In formula (7), ,

[0043] S215. Establish the International Terrestrial Reference Frame (ITRF), with the Earth's center of mass as the coordinate origin, the X-axis pointing to the intersection of the Greenwich meridian and the Earth's equator, the Z-axis pointing toward the Earth's North Pole, and the Y-axis perpendicular to the XOZ plane and forming a right-handed reference frame with the X and Z axes. The WGS84 datum is usually used.

[0044] The origin of the ICRF coordinate system and the ITRF coordinate system is the center of mass of the earth. The ICRF coordinate system is obtained by multiplying the rotation matrix Convert to ITRF coordinate system:

[0045] (8)

[0046] In formula (8), are coordinates in the Earth-fixed ground reference frame, The calculation formula is:

[0047] ;

[0048] in, They are the polar motion matrix, the Earth rotation matrix, and the precession and nutation matrix respectively.

[0049] Furthermore, the method for establishing a spaceborne single photon array laser altimeter simulation link in step S1 includes the following steps:

[0050] S11, calculating the object space three-dimensional coordinates corresponding to the array laser detection pixels;

[0051] S12, simulating signal and noise photon radiation responses, including: constructing a Delaunay triangulation using point cloud data from an airborne radar, obtaining surface reflectivity information corresponding to the wavelength of the laser based on the intensity of the point cloud, simulating a surface echo waveform [see equations (14) and (27)] and a noise waveform [see equation (29)] using an echo simulation model and a noise simulation model, respectively, and synthesizing the surface echo waveform and the noise waveform to obtain a comprehensive target echo containing both signal and noise;

[0052] S13, simulating the response of the array laser detector, including:

[0053] S131, using the pulse response function to convolve the integrated target echo to obtain the array laser altimeter system receiving echo [see formula (32)];

[0054] S132, using the Monte Carlo method to simulate the detector detection process, assuming that there are a total of p n=m*n The probability of each detection time slot is calculated based on the single-photon detector detection model [see formula (37)]. The value of the probability is compared with a random number that obeys the uniform distribution U(0,1). When the value of the probability is greater than the random number, the time tag of the corresponding time slot is obtained; when the value of the probability is ≤ the random number, the corresponding time slot is eliminated. A group of photons with time tags is obtained, and the photons in the dead zone are eliminated to obtain the photon point cloud detected by a single pixel.

[0055] S133. Repeat steps S311-S312 to simulate the photon events detected by all pixels and complete the simulation of all pixels.

[0056] Furthermore, the expression of the rigorous geometric positioning model in the step S21 of establishing the rigorous geometric positioning model of the spaceborne array laser altimeter is:

[0057] (9)

[0058] In formula (9), is the coordinate of the pixel position under ITRF, The GPS positioning system measures the phase center position of the satellite GPS antenna.

[0059] Furthermore, the method for constructing the array laser radiation transmission model in step S22 includes the following steps:

[0060] S221. Calculate the signal radiation scattered by the Lambertian body. The signal radiation includes solar radiation and laser. During the transmission process, it first contacts the atmosphere in the environment and interacts with atmospheric molecules and particles, resulting in radiation attenuation and laser beam deviation. According to the different atmospheric effects on radiation, it can be divided into: atmospheric refraction causing laser beam deviation, radiation attenuation caused by absorption and scattering of molecules and aerosol particles in the atmosphere, which is described by Lambert's law and atmospheric transmittance, as shown in formula (10); the nonlinear effect of atmospheric turbulence causes random drift, diffusion and light intensity fluctuation of the light spot, resulting in changes in the spatial distribution of laser beam energy, which is described by the Gamma distribution model, as shown in formula (11):

[0061] (10)

[0062] In formula (10), is the irradiance at the time of emission, is the returned irradiance at distance z, is the atmospheric extinction coefficient;

[0063] (11)

[0064] In formula (11), is the gamma function, is the inverse of the Rytov variance;

[0065] Obtain the atmospheric information, surface reflectivity, and geometric information at the pixel array coordinate position, and combine the effects of the atmosphere to calculate the number of photons that a single pixel can receive after the environmental response:

[0066] (12)

[0067] When the measured object is a linear single target, the number of echo photons of the entire object is expressed by the lidar equation (13):

[0068] (13)

[0069] In formula (13) are hardware fixed parameters, is the energy of the emitted laser single pulse, is the effective area of ​​the receiving system, hv is the energy of a single photon, which can be calculated using the Planck energy formula , h is Planck's constant, v is the laser frequency, c is the speed of light, is the laser wavelength. R is the distance between the laser radar and the target, is the Lambertian reflectance, T a is the one-way atmospheric transmittance, is the zenith angle of the emitted laser, is the local surface slope;

[0070] The single-pixel laser echo signal arriving at the receiving system can be represented by the convolution of the laser emission pulse and the environmental response function within the field of view of a single pixel:

[0071] (14)

[0072] In formula (14), Σ is the range of pixel occupation, is the reflectivity information of a point on the ground, For delay, Expressed using formula (15):

[0073] (15)

[0074] In formula (15), is the surface elevation at (x, y), and c is the speed of light; the second term is the time delay due to the curvature of the phase front of the laser beam, which can be ignored for spaceborne lidar.

[0075] Spatial distribution E(x,y) and temporal distribution of the laser beam Expressed as:

[0076] (16)

[0077] In formula (16), R is the distance between the laser radar and the target, θ T is the beam divergence angle, E is the energy of the emitted laser single pulse, is the root mean square pulse width of the emitted laser;

[0078] S222. Establish a background noise model to estimate the noise rate of solar background radiation scattered by the atmosphere and reflected from the ground surface to the altimeter:

[0079] (29)

[0080] In formula (29), is the wavelength-dependent spectral irradiance measured outside the planet's atmosphere. is the spectral filter bandwidth; is the field of view of the receiver in steradians (solid angle units), is half of the receiver's field of view; 、 are the zenith angle of the sun during measurement and the zenith angle of the emitted laser, respectively; is the surface reflectivity, is the angle between the sun and the normal to the Earth's surface, Expressed as:

[0081] (30)

[0082] In formula (30), is the local surface slope, is the solar azimuth.

[0083] Furthermore, for the simulation of the echo signal of the ground-based laser corner reflector used for laser altimeter satellite calibration or accuracy verification, the present invention also designs a method for simulating the cloud data of a satellite-borne array laser photon for ground-based laser corner reflector CCR. The method comprises:

[0084] Calculates signal radiation scattered from corner reflectors, including:

[0085] Considering the form of laser Gaussian beam distribution, the CCR echo photon is expressed as:

[0086] (17)

[0087] In formula (17), is the scattering cross-sectional area of ​​the corner reflector, Expressed as:

[0088] (18)

[0089] In formula (18),

[0090] is the normalized light intensity distribution, is the first-order Bessel function, θ is the diffraction angle, is the CCR aperture radius, is the peak cross-sectional area of ​​the far-field light intensity, Expressed as:

[0091] (19)

[0092] In formula (19), is the reflectivity of the coated CCR, the reflectivity of the aluminum-coated CCR is 0.78, and D=2r is the CCR aperture diameter;

[0093] Considering the dihedral error angle, the far-field normalized light amplitude of CCR is obtained according to Fraunhofer diffraction theory:

[0094] (20)

[0095] In formula (20), is the radius of CCR; is the normalized polarization complex amplitude of the nth part, for the coated CCR ; The wave number is equal to , is the laser wavelength; , ; is the angle between the outgoing beam and the incident light. If the three dihedral angle errors of CCR are equal, hour, , n refractive index is 1.46; and are the polar coordinates in the CCR coordinate system and the polar coordinates of the far-field diffraction point P, , θ is the diffraction angle, is the azimuth angle of the diffraction point P;

[0096] Simplifying formula (20) we can obtain the analytical solution of the CCR far-field normalized amplitude:

[0097] (twenty one)

[0098] In formula (21), is a first-order Bessel function, and the remaining parameters in Equation (21) are expressed as:

[0099]

[0100] According to the relationship between amplitude and light intensity, the far-field light intensity distribution of CCR reflection can be obtained as:

[0101] (twenty two)

[0102] The average normalized intensity on the diffraction angle θ ring is:

[0103] (twenty three)

[0104] Since the satellite platform is moving at high speed in space, when the CCR echo beam is reflected to the location where the laser pulse is emitted, the satellite position deviates from the beam direction by an angle, which is called the velocity difference angle. According to astrophysics, the velocity difference angle is calculated as follows:

[0105] (twenty four)

[0106] In formula (24), Re is the radius of the earth (6370 km), g is the acceleration of gravity, H is the altitude of the satellite orbit, and z is the zenith angle;

[0107] When the satellite-borne laser altimeter uses nadir measurement, the velocity difference angle is approximately:

[0108] (25)

[0109] For the satellite-borne single-photon laser altimeter platform, the orbital altitude is about 500 kilometers, and the corresponding velocity difference angle is about ;

[0110] Satellite is located at (x s ,y s ) can receive the number of photons:

[0111] (26)

[0112] In formula (26), x c with y c is the CCR coordinate;

[0113] For spaceborne lidar, when the emitted laser pulse is Gaussian and the detection target is a linear single target, the received signal according to diffraction theory can be simplified to Equation (26):

[0114] (27)

[0115] In formula (27), is the average number of photons received, the two types of objects They are expressed by formula (13) and formula (26) respectively; is the RMS pulse width of the received signal, Expressed using formula (28):

[0116] (28)

[0117] In formula (28), Expressed as the RMS pulse width of the transmitted pulse, is the surface roughness, and are the surface slopes in the along-track and perpendicular-track directions, c is the speed of light, θ Tis the laser divergence angle.

[0118] Furthermore, the method of constructing the single-photon detector response model in step S23 includes:

[0119] The pulse waveform S(t) is collected and recorded after reaching the altimeter. The impulse response function (IRF) of the altimeter is:

[0120] (31)

[0121] In formula (31), IRF is the impulse response function, k = ceil (Totaltime / Step al ) k is the number of statistical frames along the track, is the upward rounding function; IRF calculation is divided into two directions: the photon number statistics along the track and the elevation direction. is the step length of each along-track statistical frame, and Totaltime is the total along-track statistical time;

[0122] After determining the range of each along-track statistical frame, the photon point cloud within the range is statistically histogramed according to the elevation with a step length of StepH. For the The backscatter signal value of each elevation statistical box. The box where the peak backscatter signal is located is set to the elevation position of the ground surface by default and is set to p.

[0123] is the range of the impulse response function, where and It is obtained by customizing the required elevation values ​​of Surfu above the surface, Surfd below the surface, and the elevation statistics step length StepH. The number of photons above the surface is generally small, making it difficult to accurately determine the backscattered signal value above the surface. Therefore, the Surfu value should not be too large. Preferably, Surfu is set to 0.15m. The value of Surfd is based on the maximum sounding distance of the altimeter. For example, the maximum sounding distance of ICESat-2 is about 30m, so Surfd can be set to 30m. j is the total number of elevation statistics frames, which is n+m+1.

[0124] Combined with the receiving system's receiving efficiency , the photoelectric conversion quantum efficiency of the detector After the pulse response function is calculated, the laser signal and the system background noise are combined and convolved with the pulse response function to obtain the altimeter receiving echo of the entire single-photon laser altimeter system:

[0125] (32)

[0126] In formula (32), Sn (t) is the echo received by the entire single-photon laser altimeter system, S(t) is the signal echo, is the solar background noise, is the dark count noise, and the noise is integrated into ;

[0127] After passing through the filter, the laser is further transmitted to the single-photon detector. Detected in time slots The probability of a photon is expressed using a Poisson distribution:

[0128] (33)

[0129] The laser is detected by the detector after passing through the atmospheric end flow, which includes two random processes: atmospheric turbulence and detector Poisson detection. The random process of atmospheric turbulence affecting photons will affect the parameter N in the Poisson random process of detector detection of photons. The probability density of detector detection after the laser passes through atmospheric turbulence is obtained from the Mandel formula:

[0130] (34)

[0131] The probability that no photon detection occurs in a single time slot is:

[0132] (35)

[0133] The detection of a photon in a single time slot is complementary to the absence of a photon detection event in a single time slot. The probability of detecting a photon event in a single time slot is:

[0134] (36)

[0135] Most single-photon detectors will pause for a while after responding to the first incident photon before responding to subsequent incident photons, which is called a dead time. This will reduce the probability of the single-photon detector detecting the echo photon to a certain extent. If the influence of the dead time is considered, the detection probability of the single-photon detector in the i-th time slot is the probability of no photon detection during the dead time duration and the probability of detection in the i-th time slot without considering the dead time:

[0136] (37).

[0137] Furthermore, the method for evaluating the quality of spaceborne array laser simulation data under different configuration parameter conditions includes:

[0138] S31. Calculate the photon point cloud noise rate, where the point cloud noise rate is defined as the number of noise photon events recorded by a single pixel of the array laser altimeter per unit time:

[0139] (38)

[0140] In formula (38), is the noise rate defined in this paper, The number of noises recorded from 50 detections of a single pixel; is the window height, It is the total number of photons in 50 beams minus the noise obtained by the signal identified by the built-in filtering algorithm, and c is the speed of light;

[0141] Taking ICESat-2 (Natural Resources Remote Sensing Satellite) as an example, the laser transmission frequency is 10 kHz. Considering the satellite's flight speed of 7 km / s, 50 beams correspond to a satellite flight distance of about 35 meters. Since the footprint diameter of ICEsat-2 is 17.5 meters, a distance of 35 meters is equivalent to the size of two footprints.

[0142] S32. Calculate the average signal photon number. The average signal photon number is defined as the average number of signal photon events recorded by a single detection of a single pixel:

[0143] (39)

[0144] In formula (39), is the average number of signal photons, It is the total number of signal photons recorded by 50 detections of a single pixel.

[0145] S33. Calculate the detection probability. The detection probability is defined as the probability that a single pixel can detect a target in a single detection:

[0146] (40)

[0147] In formula (39), represents the detection probability, Indicates the number of signal photons recorded in 50 detections;

[0148] S34. Calculate the signal-to-noise ratio. Define the signal-to-noise ratio of altimetry data as the logarithm of the ratio of the number of signal photons to the number of noise within a 1-meter elevation range:

[0149] (41)

[0150] In formula (41), SNR is the point cloud signal-to-noise ratio, is the number of noises within the range, .

[0151] Since the echo of the altimetry measured data is very complex and it is difficult to directly obtain the pulse width of the echo, the present invention defines the signal-to-noise ratio of the altimetry data.

[0152] Furthermore, the method for solving the object space three-dimensional coordinates corresponding to the array laser detection pixel in step S11 includes: calculating the two-dimensional coordinates and pixel pointing vector of the laser detector detection pixel in the array laser radar coordinate system according to the altimeter parameters, combining the satellite attitude and orbit parameters, and intersecting with the ground reference terrain to calculate the object space three-dimensional coordinates, using atmospheric pressure, temperature, and humidity parameters to calculate the atmospheric refraction correction number to obtain actual distance information, solving the object space three-dimensional coordinates based on the geometric model of the satellite-borne array laser altimeter, and comprehensively considering the influence of tidal correction and aberration to obtain the object space three-dimensional coordinates with additional offset.

[0153] The present invention also provides a system for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array laser radar, which is used to implement the above-mentioned method for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array laser radar, comprising:

[0154] Spaceborne single-photon array laser altimeter simulation link subsystem: used to establish a spaceborne single-photon array laser altimeter simulation link;

[0155] Comprehensive simulation model construction subsystem: used to build a comprehensive simulation model of space-borne lasers and generate space-borne array laser simulation data sets;

[0156] Array laser data quality evaluation subsystem: It is used to evaluate the quality of spaceborne array laser simulation data under different configuration parameters using multiple evaluation indicators such as noise rate, average number of signal photons, detection probability, signal-to-noise ratio, and elevation accuracy.

[0157] In order to analyze the performance of domestic altimeters under different terrain conditions, the present invention uses Python to write a set of easy-to-operate programs. The main modules of the program include:

[0158] Target 3D coordinate solution module: This module supports users to plan the satellite flight path and solve the coordinates of each pixel;

[0159] Background noise calculation module: calculates the theoretical noise rate received by the pixel based on the parameters such as the sun altitude angle input by the user;

[0160] Signal echo simulation module: This module supports the calculation of the echo theoretically received by the pixel based on the parameters input by the user and the terrain data;

[0161] Detection unit response module: This module records photon point cloud data based on and using the Monte Carlo method;

[0162] Simulation data quality evaluation module: This module supports evaluating the quality of simulation point clouds based on input parameters of different specifications.

[0163] The present invention also provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the program, the steps of the method for comprehensive simulation of three-dimensional terrain mapping data of a satellite-borne array lidar are implemented as described above.

[0164] Compared with the prior art, the present invention has the following beneficial effects:

[0165] The comprehensive simulation method and system for satellite-borne array laser radar three-dimensional terrain mapping data provided by the present invention establish a satellite-borne single-photon array laser altimeter simulation link, construct a satellite-borne laser comprehensive simulation model including an array laser geometric positioning model, a radiation transmission model, and a single-photon detection model, and generate a satellite-borne array laser simulation data set using the parameters of a domestic satellite type as an example; and use multiple evaluation indicators to evaluate the quality of satellite-borne array laser simulation data under different parameter configuration conditions, providing a solid foundation for the development of array laser three-dimensional terrain mapping satellites. BRIEF DESCRIPTION OF THE DRAWINGS

[0166] Various other advantages and benefits will become apparent to those skilled in the art by reading the following detailed description of the preferred embodiment.The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present invention.

[0167] In the attached figure:

[0168] Figure 1 This is a flow chart of simulation of spaceborne single-photon array laser altimetry data according to an embodiment of the present invention;

[0169] Figure 2 This is a schematic diagram of three-dimensional coordinate solution of a satellite-borne single-photon array laser target according to an embodiment of the present invention;

[0170] Figure 3 Schematic diagram of the angle between pixel vectors in the laser radar coordinate system according to an embodiment of the present invention;

[0171] Figure 4 Schematic diagram of speed difference angle according to an embodiment of the present invention;

[0172] Figure 5 This is a working timing diagram of the single photon detection system according to an embodiment of the present invention;

[0173] Figure 6 This is a schematic diagram of the storage format of the simulation data set in h5 format according to an embodiment of the present invention;

[0174] Figure 7 This is a GUI interface diagram of a program written in Python according to an embodiment of the present invention;

[0175] Figure 8A simple terrain model diagram of an embodiment of the present invention;

[0176] Figure 9 This is a diagram showing a simple terrain simulation result according to an embodiment of the present invention;

[0177] Figure 10 This is a diagram of CCR deployment and satellite-borne laser simulation data according to an embodiment of the present invention;

[0178] Figure 11 This is a mountain airborne point cloud and satellite flight trajectory design diagram according to an embodiment of the present invention;

[0179] Figure 12 A point cloud image of a satellite-borne array laser simulation in a mountainous area according to an embodiment of the present invention;

[0180] Figure 13 This is a diagram of the urban airborne point cloud and satellite flight trajectory design according to an embodiment of the present invention;

[0181] Figure 14 A point cloud image of a satellite-borne array laser simulation of an urban area according to an embodiment of the present invention;

[0182] Figure 15 Schematic diagram of the structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0183] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, like numbers in different figures represent like or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present disclosure. Rather, they are merely examples of devices and products consistent with certain aspects of the present disclosure, as detailed in the appended claims.

[0184] The terms used in this disclosure are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. As used in this disclosure and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0185] It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining."

[0186] The embodiments of the present invention are described in further detail below.

[0187] An embodiment of the present invention provides a method for comprehensive simulation of three-dimensional terrain mapping data of a spaceborne array laser radar, comprising the following steps:

[0188] S1. Establishing a spaceborne array lidar 3D terrain mapping simulation link, including the following steps:

[0189] S11. Calculate the object space three-dimensional coordinates corresponding to the array laser detection pixel, including: calculating the two-dimensional coordinates and pixel pointing vector of the laser detector detection pixel in the array laser radar coordinate system according to the altimeter parameters, combining the satellite attitude and orbit parameters, and calculating the object space three-dimensional coordinates by intersecting with the ground reference terrain, using the atmospheric pressure, temperature, and humidity parameters to calculate the atmospheric refraction correction number to obtain the actual distance information, and calculating the object space three-dimensional coordinates based on the geometric model of the satellite-borne array laser altimeter, and comprehensively considering the influence of tidal correction and aberration to obtain the object space three-dimensional coordinates with additional offset.

[0190] S12, simulating signal and noise photon radiation responses, including: constructing a Delaunay triangulation using point cloud data from an airborne radar, obtaining surface reflectivity information corresponding to the wavelength of the laser based on the intensity of the point cloud, simulating a surface echo waveform [see equations (14) and (27)] and a noise waveform [see equation (29)] using an echo simulation model and a noise simulation model, respectively, and synthesizing the surface echo waveform and the noise waveform to obtain a comprehensive target echo containing both signal and noise;

[0191] S13, simulating the response of the array laser detector, including:

[0192] S131, using the pulse response function to convolve the integrated target echo to obtain the array laser altimeter system receiving echo [see formula (32)];

[0193] S132, using the Monte Carlo method to simulate the detector detection process, assuming that there are The probability of each detection time slot is calculated based on the single-photon detector detection model [see formula (37)]. The value of the probability is compared with a random number that obeys the uniform distribution U(0,1). When the value of the probability is greater than the random number, the time tag of the corresponding time slot is obtained; when the value of the probability is ≤ the random number, the corresponding time slot is eliminated. A group of photons with time tags is obtained, and the photons in the dead zone are eliminated to obtain the photon point cloud detected by a single pixel.

[0194] S133. Repeat steps S311-S312 to simulate the photon events detected by all pixels and complete the simulation of all pixels.

[0195] S2. Construct a comprehensive simulation model for three-dimensional terrain mapping by spaceborne array lidar and generate a three-dimensional terrain simulation dataset by spaceborne array lidar.

[0196] The method for constructing a satellite-borne laser comprehensive simulation model includes the following steps:

[0197] S21. Constructing a rigorous geometric positioning model for the array laser, including: performing relevant coordinate system definitions and conversions, including the following steps:

[0198] S211, establish array laser radar coordinate system (O L -X L Y L Z L ); take the lens center of the laser radar imaging system as the coordinate origin O L , the Z axis is perpendicular to the focal plane of the detector and points to the nadir direction, and the X axis and Y axis are parallel to the edge of the focal plane array and form a right-handed system with the Z axis;

[0199] Assume that the distance between the optical center of the laser detector and the focal plane is , the coordinates of the array center in the laser radar coordinate system are expressed as (0, 0, - ), suppose the detector array has n rows and m columns, m and n are even numbers, and the pixel size is , taking the first pixel in the upper right corner of the detector array as the pixel in the first row and first column, the coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are expressed as:

[0200] , ;

[0201] The coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are calculated to obtain formula (1):

[0202] (1)

[0203] The angle between the pixel and the pointing vector of the corresponding ground point in the laser radar coordinates is as follows: Figure 3 As shown;

[0204] The three-dimensional coordinates (XYZ) TL of the corresponding ground laser footprint point are expressed in the lidar coordinate system as formula (2):

[0205] (2)

[0206] In formula (1) and (2), Obtain the distance value from the pixel position to the target for the lidar system; The projection is in X L O L Y L Plane and X L The angle between the positive directions of the axes; To point to Z L The angle between the positive directions of the axes;

[0207] S212, establish the satellite body coordinate system ( B -X B Y B Z B ); define the satellite body coordinate system as follows: the satellite mass center is the coordinate system origin O B , the X-axis points to the flight direction, the Z-axis points to the nadir, and the direction of the Y-axis is determined by the right-hand rule;

[0208] The position of the ground point in the array lidar coordinate system is converted to the satellite body coordinate system through coordinate translation and rotation transformation:

[0209] (3)

[0210] In formula (3), is the coordinate of the ground point in the satellite coordinate system, is the rotation matrix of the array lidar transformed to the satellite body coordinate system, is the offset between the center of the array lidar lens and the origin of the satellite body coordinate system;

[0211] S213, establish orbital coordinate system (O O -X O Y O Z O ); The origin of the orbital coordinate system is the satellite's center of mass, the X-axis points to the satellite's flight direction, the Z-axis points to the center of the earth, and the Y-axis is perpendicular to the XOZ plane and forms a right-handed system with the X-axis and Z-axis;

[0212] The coordinate centers of the satellite body coordinate system and the orbital coordinate system are consistent. Only three-axis rotation is required to complete the coordinate transformation from the satellite body coordinate system to the orbital coordinate system:

[0213] (4)

[0214] In formula (4), is the coordinate of the ground point in the orbital coordinate system; is the rotation matrix for transforming the satellite body coordinate system to the orbit coordinate system, The three attitude angles of the satellite determined by the star sensor: roll angle , pitch angle , yaw angle composition:

[0215] (5)

[0216] S214. Establish a spatially fixed inertial reference system. Use the Earth's center of mass as the coordinate origin, the X-axis pointing to the vernal equinox, the Z-axis pointing to the celestial north pole, and the Y-axis perpendicular to the XOZ plane to form a right-handed system with the X-axis and Z-axis. Use the J2000 coordinate system.

[0217] The orbital coordinate system is transformed into the ICRF coordinate system by coordinate translation and rotation:

[0218] (6)

[0219] In formula (6), is the offset between the origin of the orbital coordinate system and the origin of the ICRF coordinate system in the ICRF coordinate system. To solve the rotation matrix from the orbital coordinate system to the ICRF coordinate system, the position vector of the satellite in the ICRF coordinate system at time t is required. and the velocity vector , the calculation expression of the rotation matrix between the orbital coordinate system and the ICRF coordinate system is:

[0220] (7)

[0221] In formula (7),

[0222] S215. Establish an Earth-fixed terrestrial reference system with the Earth's center of mass as the coordinate origin, the X-axis pointing to the intersection of the Greenwich meridian and the Earth's equator, the Z-axis pointing toward the Earth's North Pole, and the Y-axis perpendicular to the XOZ plane and forming a right-handed system with the X-axis and Z-axis, using the WGS84 datum.

[0223] The origin of ICRF coordinate system and ITRF coordinate system is the center of mass of the earth. ICRF coordinate system is obtained by multiplying the rotation matrix Convert to ITRF coordinate system:

[0224] (8)

[0225] In formula (8), are coordinates in the Earth-fixed ground reference frame, The calculation formula is:

[0226] ;

[0227] Among them, W(t), R(t), and PN(t) are the polar motion matrix, the Earth rotation matrix, and the precession and nutation matrix, respectively.

[0228] Based on the defined and transformed coordinate system, a rigorous geometric positioning model of the spaceborne array laser altimeter is established. The expression of the rigorous geometric positioning model is:

[0229] (9)

[0230] In formula (9), is the coordinate of the pixel position under ITRF, The GPS positioning system measures the phase center position of the satellite GPS antenna.

[0231] The rigorous geometric positioning model of the spaceborne array laser altimeter constructed in this embodiment is as follows: Figure 2 As shown;

[0232] S22. Constructing an array laser radiation transmission model, including the following steps:

[0233] S221. Calculate the signal radiation scattered by the Lambertian body. The signal radiation includes solar radiation and laser. During the transmission process, it first contacts the atmosphere in the environment and interacts with atmospheric molecules and particles, resulting in radiation attenuation and laser beam deviation. According to the different atmospheric effects on radiation, it can be divided into: atmospheric refraction causing laser beam deviation, radiation attenuation caused by absorption and scattering of molecules and aerosol particles in the atmosphere, which is described by Lambert's law and atmospheric transmittance, as shown in formula (10); the nonlinear effect of atmospheric turbulence causes random drift, diffusion and light intensity fluctuation of the light spot, resulting in changes in the spatial distribution of laser beam energy, which is described by the Gamma distribution model, as shown in formula (11):

[0234] (10)

[0235] In formula (10), is the irradiance at the time of emission, is the returned irradiance at distance z, is the atmospheric extinction coefficient;

[0236] (11)

[0237] In formula (11), is the gamma function, m is the inverse of the Rytov variance;

[0238] Obtain the atmospheric information, surface reflectivity, and geometric information at the pixel array coordinate position, and combine the effects of the atmosphere to calculate the number of photons that a single pixel can receive after the environmental response:

[0239] (12)

[0240] When the measured object is a linear single target, the number of echo photons of the entire object is expressed by the lidar equation (13):

[0241] (13)

[0242] In formula (13) are hardware fixed parameters, is the energy of the emitted laser single pulse, is the effective area of ​​the receiving system, is the energy of a single photon, which can be calculated using the Planck energy formula , is Planck's constant, is the laser frequency, c is the speed of light, is the laser wavelength. R is the distance between the laser radar and the target, is the Lambertian reflectance, T a is the one-way atmospheric transmittance, θ p is the zenith angle of the emitted laser, is the local surface slope;

[0243] The single-pixel laser echo signal arriving at the receiving system can be represented by the convolution of the laser emission pulse and the environmental response function within the field of view of a single pixel:

[0244] (14)

[0245] In formula (14), Σ is the range of pixel occupation, is the reflectivity information of a point on the ground, For delay, Expressed using formula (15):

[0246] (15)

[0247] In formula (15), is the surface elevation at (x, y), c is the speed of light;

[0248] Spatial distribution E(x,y) and temporal distribution of the laser beam Expressed as:

[0249] (16)

[0250] In formula (16), R is the distance between the laser radar and the target, θ T is the beam divergence angle, E is the energy of the emitted laser single pulse, is the root mean square pulse width of the emitted laser;

[0251] S222. Establish a background noise model to estimate the noise rate of solar background radiation scattered by the atmosphere and reflected from the ground surface to the altimeter:

[0252] (29)

[0253] In formula (29), is the wavelength-dependent spectral irradiance measured outside the planet's atmosphere. is the spectral filter bandwidth; is the field of view of the receiver in steradians (solid angle units), is half of the receiver's field of view; 、 are the zenith angle of the sun during measurement and the zenith angle of the emitted laser, respectively; is the surface reflectivity, is the angle between the sun and the normal to the Earth's surface, Expressed as:

[0254] (30)

[0255] In formula (30), is the local surface slope, is the solar azimuth.

[0256] The integrated simulation method for spaceborne array laser radar three-dimensional terrain mapping data of this embodiment also includes designing a spaceborne array laser photon cloud data simulation method for ground laser corner reflectance CCR. The spaceborne array laser photon cloud data simulation method for ground laser corner reflectance CCR includes:

[0257] Calculates signal radiation scattered from corner reflectors, including:

[0258] Considering the form of laser Gaussian beam distribution, the CCR echo photon is expressed as:

[0259] (17)

[0260] In formula (17), δ(θ) is the scattering cross-sectional area of ​​the corner reflector, and δ(θ) is expressed as:

[0261] (18)

[0262] In formula (18), is the normalized light intensity distribution, is the first-order Bessel function, θ is the diffraction angle, r is the CCR aperture radius, is the peak cross-sectional area of ​​the far-field light intensity, Expressed as:

[0263] (19)

[0264] In formula (19), is the reflectivity of the coated CCR, the reflectivity of the aluminum-coated CCR is 0.78, and D=2r is the CCR aperture diameter;

[0265] According to Fraunhofer diffraction theory, the far-field normalized light amplitude of CCR is obtained:

[0266] (20)

[0267] In formula (20), is the radius of CCR; is the normalized polarization complex amplitude of the nth part, for the coated CCR ; The wave number is equal to , is the laser wavelength; , ; θ0 is the angle between the outgoing beam and the incident light. If the three dihedral angle errors of CCR are equal to β, , Refractive index is 1.46; and are the polar coordinates in the CCR coordinate system and the polar coordinates of the far-field diffraction point P, , θ is the diffraction angle, is the azimuth angle of the diffraction point P;

[0268] Simplifying formula (20) we can obtain the analytical solution of the CCR far-field normalized amplitude:

[0269] (twenty one)

[0270] In formula (21), is a first-order Bessel function, and the remaining parameters in Equation (21) are expressed as:

[0271]

[0272] According to the relationship between amplitude and light intensity, the far-field light intensity distribution of CCR reflection can be obtained as:

[0273] (twenty two)

[0274] At the diffraction angle The average normalized intensity on the ring is:

[0275] (twenty three)

[0276] Since the satellite platform moves at high speed in space, when the CCR echo beam is reflected to the position where the laser pulse is emitted, the satellite position deviates from the beam direction by an angle, which is called the velocity difference angle. Figure 4 As shown, according to the knowledge of astrophysics, the calculation formula of the velocity difference angle is:

[0277] (twenty four)

[0278] In formula (24), Re is the radius of the earth (6370 km), g is the acceleration of gravity, H is the altitude of the satellite orbit, and z is the zenith angle;

[0279] When the satellite-borne laser altimeter uses nadir measurement, the velocity difference angle is approximately:

[0280] (25)

[0281] The orbital altitude of the satellite-borne single-photon laser altimeter platform is about 500 kilometers, and the corresponding velocity difference angle is about ;

[0282] Satellite is located at (x s ,y s ) can receive the number of photons:

[0283] (26)

[0284] In formula (26), x c with y c is the CCR coordinate;

[0285] For spaceborne lidar, when the emitted laser pulse is Gaussian and the detection target is a linear single target, the received signal according to diffraction theory can be simplified to Equation (26):

[0286] (27)

[0287] In formula (27), Ns is the average number of received photons. The Ns of the two types of objects are expressed by formula (13) and formula (26) respectively; is the RMS pulse width of the received signal, Expressed using formula (28):

[0288] (28)

[0289] In formula (28), Expressed as the RMS pulse width of the transmitted pulse, is the surface roughness, and are the surface slopes in the along-track and perpendicular-track directions, c is the speed of light, θ T is the laser divergence angle;

[0290] S23. Construct a single-photon detector response model, including:

[0291] The pulse waveform S(t) is collected and recorded after reaching the altimeter. The impulse response function of the altimeter is:

[0292] (31)

[0293] In formula (31), IRF is the impulse response function, k = ceil (Totaltime / Step al ) k is the number of statistical frames along the track, is the upward rounding function; IRF calculation is divided into two directions: the photon number statistics along the track and the elevation direction. al is the step length of each along-track statistical frame, and Totaltime is the total along-track statistical time;

[0294] After determining the range of each along-track statistical frame, the photon point cloud within the range is statistically histogramed according to the elevation. The step length is StepH, β(z j ) is the backscatter signal value of the j-th elevation statistical frame, and the frame where the peak backscatter signal is located is defaulted to the elevation position of the surface and is set to p;

[0295] [pn,p+m] is the range of the impulse response function, where and It is obtained by customizing the required Surfu above the surface, Surfd below the surface, and the elevation statistics step size StepH. The number of photons above the surface is generally small, making it difficult to accurately calculate the backscattered signal value above the surface. Therefore, the Surfu value should not be too large, and the Surfu value is 0.15m. The Surfd value is based on the altimeter's maximum sounding distance. The ICESat-2 maximum sounding distance is approximately 30m, so Surfd is set to 30m. j is the total number of elevation statistics frames, which is n+m+1.

[0296] Combined with the receiving system's receiving efficiency , the photoelectric conversion quantum efficiency of the detector After the pulse response function is calculated, the laser signal and the system background noise are combined and convolved with the pulse response function to obtain the altimeter receiving echo of the entire single-photon laser altimeter system:

[0297] (32)

[0298] In formula (32), is the echo received by the entire single-photon laser altimeter system, is the signal echo, is the solar background noise, is the dark count noise, and the noise is integrated into ;

[0299] After passing through the filter, the laser is further transmitted to the single-photon detector. The probability of the single-photon detector detecting k photons in the i-th time slot is expressed by Poisson distribution:

[0300] (33)

[0301] The laser is detected by the detector after passing through the atmospheric end flow, which includes two random processes: atmospheric turbulence and detector Poisson detection. The random process of atmospheric turbulence affecting photons will affect the parameter N in the Poisson random process of detector detection of photons. The probability density of detector detection after the laser passes through atmospheric turbulence is obtained from the Mandel formula:

[0302] (34)

[0303] The probability that no photon detection occurs in a single time slot is:

[0304] (35)

[0305] The detection of a photon in a single time slot is complementary to the absence of a photon detection event in a single time slot. The probability of detecting a photon in a single time slot is:

[0306] (36)

[0307] Most single-photon detectors will pause for a while after responding to the first incident photon before responding to the subsequent incident photons, that is, there is a dead time, which will reduce the probability of the single-photon detector detecting the echo photon to a certain extent. Figure 5 As shown, considering the influence of the dead zone, the detection probability of the single-photon detector in the i-th time slot is the probability that no photon detection occurs during the duration of the dead zone and the probability that the i-th time slot is detected when the dead zone is not considered:

[0308] (37).

[0309] S3. Use multiple evaluation indicators such as noise rate, average signal photon number, detection probability, signal-to-noise ratio, and elevation accuracy to evaluate the quality of spaceborne array laser simulation data under different configuration parameters.

[0310] Methods for evaluating the quality of spaceborne array laser simulation data under different configuration parameters include:

[0311] S31. Calculate the photon point cloud noise rate, where the point cloud noise rate is defined as the number of noise photon events recorded by a single pixel of the array laser altimeter per unit time:

[0312] (38)

[0313] In formula (38), is the noise rate defined in this paper, The number of noises recorded from 50 detections of a single pixel; is the window height, It is the total number of photons in 50 beams minus the noise obtained by the signal identified by the built-in filtering algorithm, and c is the speed of light;

[0314] S32. Calculate the average signal photon number. The average signal photon number is defined as the average number of signal photon events recorded by a single detection of a single pixel:

[0315] (39)

[0316] In formula (39), is the average number of signal photons, It is the total number of signal photons recorded by 50 detections of a single pixel.

[0317] S33. Calculate the detection probability. The detection probability is defined as the probability that a single pixel can detect a target in a single detection:

[0318] (40)

[0319] In formula (39), represents the detection probability, Indicates the number of signal photons recorded in 50 detections;

[0320] S34. Calculate the signal-to-noise ratio. Define the signal-to-noise ratio of altimetry data as the logarithm of the ratio of the number of signal photons to the number of noise within a 1-meter elevation range:

[0321] (41)

[0322] In formula (41), SNR is the point cloud signal-to-noise ratio, is the number of noises within the range, .

[0323] Figure 1 The simulation process of satellite-borne single-photon array laser altimetry data in this embodiment is shown.

[0324] The embodiment of the present invention further provides a system for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array lidar, which is used to implement the above-mentioned method for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array lidar, including:

[0325] Spaceborne single-photon array laser altimeter simulation link subsystem: used to establish a spaceborne single-photon array laser altimeter simulation link;

[0326] Comprehensive simulation model construction subsystem: used to build a comprehensive simulation model of space-borne lasers and generate space-borne array laser simulation data sets;

[0327] Array laser data quality evaluation subsystem: It is used to evaluate the quality of spaceborne array laser simulation data under different configuration parameters using multiple evaluation indicators such as noise rate, average number of signal photons, detection probability, signal-to-noise ratio, and elevation accuracy.

[0328] This embodiment designs the specifications of the simulation data file (simulation data set) based on the data characteristics of the array laser. The format of the output data is .h5 format, which contains three groups: The MetaData group is a metadata description that records the parameters such as the number of beams set during the simulation, the specifications of the detector array, and the simulation time. The heights group and the quality_assessment group respectively store the coordinate information and quality evaluation information corresponding to each pixel. The data sets contained in the heights group are: the laser emission time delta_time, the elevation height of each point cloud, the label signal_label of the signal and noise photons, and the plane position information x, y of each point cloud. The data sets contained in the quality_assessment group are the quality evaluation indicators of the point cloud data accumulated by 50 detections of a single pixel, which are: signal-to-noise ratio SNR, background noise rate bckgrd, detection probability prd, and average signal photon number signal_mean, such as Figure 6 This embodiment uses Python to write a set of easy-to-operate programs, and the GUI interface of the program is as follows Figure 7 shown.

[0329] In an application example of a certain type of satellite to be launched (see Table 1), an embodiment of the present invention carries out a satellite-borne array laser simulation practice.

[0330] Table 1 Parameter settings of a certain type of satellite

[0331]

[0332]

[0333] Simple terrain:

[0334] In order to facilitate the subsequent point cloud data processing, different terrain satellite altimetry data were simulated, using built-in flat land, stepped land, terraced land, and inverted terraced land. Figure 8 As shown in the figure, the reflectivity is set to 0.3, the solar altitude angle is 80° (representing strong background radiation), and the altimeter parameters in Table 1 are used to simulate the altimeter data of these simple terrains. Figure 9 To better display the simulation results of different terrains, Figure 9 Except for the flat terrain which displays the noise point cloud, the simulation results of other terrains only display the signal point cloud.

[0335] CCR echo photons:

[0336] The altimeter in Table 1 has only a single channel, a deadband of 250 ns, a pixel size of 8.3 meters, a repetition rate of 1 kHz, and a ground sampling interval of 7 meters. These parameters make this altimeter unsuitable for detecting CCR targets. To demonstrate the simulation results of the above process for CCR targets, this example uses the ICESat-2 / ATLAS altimeter parameters (see Table 2). The CCR parameters and their deployment locations are shown in Table 3.

[0337] Table 2 ICESat-2 / ATLAS altimeter parameters

[0338]

[0339]

[0340] Table 3 CCR parameters and their layout locations used for simulation

[0341]

[0342] Figure 10 The CCR layout and satellite-borne laser simulation data of this embodiment are shown.

[0343] Actual terrain:

[0344] Two types of terrain are selected: urban and mountainous. The urban terrain area mainly includes three types of land features: buildings, vegetation, and water bodies. The point cloud density is 23.29 pts / m 2 The mountainous terrain area is high in the west and low in the east. The west is dominated by mountains, while the east is a flat area formed by perennial rain. The point cloud density is 9.86 pts / m 2 . Point cloud data rendering and drawn flight trajectory as shown Figure 11 、 Figure 13 The urban area satellite array laser simulation point cloud is shown in Figure 12 、 Figure 14 shown.

[0345] An embodiment of the present invention further provides a computer device, Figure 15 This is a schematic diagram of the structure of a computer device provided by an embodiment of the present invention; see the accompanying drawings Figure 15 As shown, the computer device includes: an input device 23, an output device 24, a memory 22 and a processor 21; the memory 22 is used to store one or more programs; when the one or more programs are executed by the one or more processors 21, the one or more processors 21 implement the method for comprehensive simulation of three-dimensional terrain mapping data of a space-borne array laser radar as provided in the above embodiment; wherein the input device 23, the output device 24, the memory 22 and the processor 21 can be connected by a bus or other means, Figure 15 The bus connection is taken as an example.

[0346] The memory 22, as a readable and writable storage medium of a computing device, can be used to store software programs and computer executable programs, such as program instructions corresponding to the method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array lidar, as described in an embodiment of the present invention. The memory 22 may primarily include a program storage area and a data storage area. The program storage area may store an operating system and at least one application required for a function; the data storage area may store data created based on the use of the device. In addition, the memory 22 may include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 22 may further include memory remotely located relative to the processor 21, and such remote memory may be connected to the device via a network. Examples of the aforementioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0347] The input device 23 may be used to receive input digital or character information, and generate key signal input related to user settings and function control of the device; the output device 24 may include a display device such as a display screen.

[0348] The processor 21 executes various functional applications and data processing of the device by running the software programs, instructions and modules stored in the memory 22, that is, realizes the above-mentioned comprehensive simulation method of three-dimensional terrain mapping data of the satellite-borne array lidar.

[0349] The computer device provided above can be used to execute the comprehensive simulation method of satellite-borne array lidar three-dimensional terrain mapping data provided in the above embodiment, and has corresponding functions and beneficial effects.

[0350] An embodiment of the present invention also provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform the method for comprehensive simulation of three-dimensional terrain mapping data of a space-borne array lidar as provided in the above embodiment. The storage medium is any of various types of memory devices or storage devices, including: installation media, such as CD-ROMs, floppy disks, or tape devices; computer system memory or random access memory, such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; non-volatile memory, such as flash memory, magnetic media (such as hard disks or optical storage); registers or other similar types of memory elements; the storage medium may also include other types of memory or a combination thereof; in addition, the storage medium may be located in the first computer system in which the program is executed, or may be located in a different second computer system, the second computer system being connected to the first computer system via a network (such as the Internet); the second computer system may provide program instructions to the first computer for execution. The storage medium includes two or more storage media that may reside in different locations (e.g., in different computer systems connected via a network). The storage medium may store program instructions (e.g., embodied as a computer program) that can be executed by one or more processors.

[0351] Of course, the storage medium containing computer-executable instructions provided in an embodiment of the present invention is not limited to the comprehensive simulation method for three-dimensional terrain surveying and mapping data of a satellite-borne array lidar as described in the above embodiment, and can also execute related operations in the comprehensive simulation method for three-dimensional terrain surveying and mapping data of a satellite-borne array lidar provided in any embodiment of the present invention.

[0352] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0353] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A comprehensive simulation method for three-dimensional terrain mapping data of a spaceborne array laser radar, characterized in that: The following steps are involved: S1. Establish a simulation link for three-dimensional terrain mapping by a spaceborne array lidar; S2. Construct a comprehensive simulation model for three-dimensional terrain mapping by spaceborne array lidar and generate a three-dimensional terrain simulation dataset by spaceborne array lidar. S3. Use multiple evaluation indicators such as noise rate, average signal photon number, detection probability, signal-to-noise ratio, and elevation accuracy to evaluate the quality of spaceborne array laser simulation data under different configuration parameters. The method for constructing a satellite-borne laser comprehensive simulation model in step S2 includes the following steps: S21. Construct a rigorous geometric positioning model for array lasers, including: Perform relevant coordinate system definitions and conversions; Based on the defined and transformed coordinate system, a rigorous geometric positioning model of the spaceborne array laser altimeter is established; S22. Construct array laser radiation transmission model; S23. Construct a single-photon detector response model.

2. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 1, characterized in that: The method for performing the relevant coordinate system definition and conversion in step S21 includes the following steps: S211, establish array laser radar coordinate system (O L -X L Y L Z L ); take the lens center of the laser radar imaging system as the coordinate origin O L , the Z axis is perpendicular to the focal plane of the detector and points to the nadir direction, and the X axis and Y axis are parallel to the edge of the focal plane array and form a right-handed system with the Z axis; Assume that the distance between the optical center of the laser detector and the focal plane is , the coordinates of the array center in the laser radar coordinate system are expressed as (0, 0, - ), suppose the detector array has n rows and m columns, m and n are even numbers, and the pixel size is , taking the first pixel in the upper right corner of the detector array as the pixel in the first row and first column, the coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are expressed as: ； The coordinates of the pixel in the rth row and cth column in the array lidar coordinate system are calculated to obtain formula (1): （1） The three-dimensional coordinates of the corresponding ground laser footprint points In the laser radar coordinate system, it is expressed as formula (2): （2） In formula (1) and (2), Obtain the distance value from the pixel position to the target for the lidar system; The projection is in X L O L Y L Plane and X L The angle between the positive directions of the axes; To point to Z L The angle between the positive directions of the axes; S212, establish the satellite body coordinate system ( B -X B Y B Z B ); define the satellite body coordinate system as follows: the satellite mass center is the coordinate system origin O B , the X-axis points to the flight direction, the Z-axis points to the nadir, and the direction of the Y-axis is determined by the right-hand rule; The position of the ground point in the array lidar coordinate system is converted to the satellite body coordinate system through coordinate translation and rotation transformation: （3） In formula (3), is the coordinate of the ground point in the satellite coordinate system, is the rotation matrix of the array lidar transformed to the satellite body coordinate system, is the offset between the center of the array lidar lens and the origin of the satellite body coordinate system; S213, establish orbital coordinate system (O O -X O Y O Z O ); The origin of the orbital coordinate system is the satellite's center of mass, the X-axis points to the satellite's flight direction, the Z-axis points to the center of the earth, and the Y-axis is perpendicular to the XOZ plane and forms a right-handed system with the X-axis and Z-axis; The coordinate transformation from the satellite body coordinate system to the orbital coordinate system is completed by rotating the three axes of the coordinates: （4） In formula (4), is the coordinate of the ground point in the orbital coordinate system; is the rotation matrix for transforming the satellite body coordinate system to the orbit coordinate system, The three attitude angles of the satellite determined by the star sensor: roll angle , pitch angle , yaw angle composition: （5） S214. Establish a spatially fixed inertial reference system; take the Earth's center of mass as the coordinate origin, with the X-axis pointing to the vernal equinox, the Z-axis pointing to the celestial north pole, and the Y-axis perpendicular to the XOZ plane and forming a right-handed system with the X-axis and Z-axis. The orbital coordinate system is transformed into the ICRF coordinate system by coordinate translation and rotation: （6） In formula (6), is the offset between the origin of the orbital coordinate system and the origin of the ICRF coordinate system in the ICRF coordinate system. To solve the rotation matrix from the orbital coordinate system to the ICRF coordinate system, the position vector of the satellite in the ICRF coordinate system at time t is required. and the velocity vector , the calculation expression of the rotation matrix between the orbital coordinate system and the ICRF coordinate system is: （7） In formula (7), ; S215. Establish an Earth-fixed ground reference system; with the Earth's center of mass as the coordinate origin, the X-axis pointing to the intersection of the Greenwich meridian and the Earth's equator, the Z-axis pointing toward the Earth's North Pole, and the Y-axis perpendicular to the XOZ plane and forming a right-handed system with the X-axis and Z-axis; The origin of ICRF coordinate system and ITRF coordinate system is the center of mass of the earth. ICRF coordinate system is obtained by multiplying the rotation matrix Convert to ITRF coordinate system: （8） In formula (8), are coordinates in the Earth-fixed ground reference frame, The calculation formula is: ； Among them, W(t), R(t), and PN(t) are the polar motion matrix, the Earth rotation matrix, and the precession and nutation matrix, respectively.

3. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 1, characterized in that: The method for establishing a spaceborne single photon array laser altimeter simulation link in step S1 comprises the following steps: S11, calculating the object space three-dimensional coordinates corresponding to the array laser detection pixels; S12. Simulating signal and noise photon radiation responses, including: constructing a Delaunay triangulation using point cloud data from the airborne radar, obtaining surface reflectivity information corresponding to the laser wavelength based on the intensity of the point cloud, simulating a surface echo waveform and a noise waveform using an echo simulation model and a noise simulation model, respectively, and combining the surface echo waveform and the noise waveform to obtain a composite target echo containing both signal and noise; S13, simulating the response of the array laser detector, including: S131, using the pulse response function to convolve the integrated target echo to obtain the array laser altimeter system receiving echo; S132, using the Monte Carlo method to simulate the detector detection process, assuming that there are The probability of each detection time slot is calculated based on the single-photon detector detection model. The value of the probability is compared with a random number that obeys the uniform distribution U(0,1). When the value of the probability is greater than the random number, the time tag of the corresponding time slot is obtained; when the value of the probability is ≤ the random number, the corresponding time slot is eliminated. A group of photons with time tags is obtained, and the photons in the dead zone are eliminated to obtain the photon point cloud detected by a single pixel. S133. Repeat steps S311-S312 to simulate the photon events detected by all pixels and complete the simulation of all pixels.

4. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 2, characterized in that: The expression of the strict geometric positioning model in the strict geometric positioning model of the spaceborne array laser altimeter established in step S21 is: （9） In formula (9), is the coordinate of the pixel position under ITRF, The GPS positioning system measures the phase center position of the satellite GPS antenna; The method for constructing the array laser radiation transmission model in step S22 comprises the following steps: S221. Calculate the signal radiation scattered by the Lambertian body. The signal radiation includes solar radiation and laser. During the transmission process, it first contacts the atmosphere in the environment and interacts with atmospheric molecules and particles, resulting in radiation attenuation and laser beam deviation. According to the different atmospheric effects on radiation, it can be divided into: atmospheric refraction causing laser beam deviation, radiation attenuation caused by absorption and scattering of molecules and aerosol particles in the atmosphere, which is described by Lambert's law and atmospheric transmittance, as shown in formula (10); the nonlinear effect of atmospheric turbulence causes random drift, diffusion and light intensity fluctuation of the light spot, resulting in changes in the spatial distribution of laser beam energy, which is described by the Gamma distribution model, as shown in formula (11): （10） In formula (10), is the irradiance at the time of emission, is the returned irradiance at distance z, is the atmospheric extinction coefficient; （11） In formula (11), is the gamma function, m is the inverse of the Rytov variance; Obtain the atmospheric information, surface reflectivity, and geometric information at the pixel array coordinate position, and combine the effects of the atmosphere to calculate the number of photons that a single pixel can receive after the environmental response: （12） When the measured object is a linear single target, the number of echo photons of the entire object is expressed by the lidar equation (13): （13） In formula (13), C h is a hardware fixed parameter, E t is the energy of the single laser pulse, A r is the effective area of ​​the receiving system, hv is the energy of a single photon, which can be calculated using the Planck energy formula to obtain hv=hc / λ, where h is the Planck constant, v is the laser frequency, c is the speed of light, and λ is the laser wavelength; R is the distance between the lidar and the target, ρ is the Lambertian reflectivity, and T a is the one-way atmospheric transmittance, θ p is the zenith angle of the emitted laser, is the local surface slope; The single-pixel laser echo signal arriving at the receiving system can be represented by the convolution of the laser emission pulse and the environmental response function within the field of view of a single pixel: （14） In formula (14), Σ is the range of the pixel, β(x, y, R) is the reflectivity information of a point on the ground, For delay, Expressed using formula (15): （15） In formula (15), is the surface elevation at (x, y), c is the speed of light; Spatial distribution E(x,y) and temporal distribution of the laser beam Expressed as: （16） In formula (16), R is the distance between the laser radar and the target, θ T is the beam divergence angle, E is the energy of the emitted laser single pulse, is the root mean square pulse width of the emitted laser; S222. Establish a background noise model to estimate the noise rate of solar background radiation scattered by the atmosphere and reflected from the ground surface to the altimeter: （29） In formula (29), is the wavelength-dependent spectral irradiance measured outside the planet's atmosphere. is the spectral filter bandwidth; is the field of view of the receiver in steradians (solid angle units), is half of the receiver's field of view; 、 are the zenith angle of the sun during measurement and the zenith angle of the emitted laser, respectively; is the surface reflectivity, is the angle between the sun and the normal to the Earth's surface, Expressed as: （30） In formula (30), is the local surface slope, is the solar azimuth.

5. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 2, characterized in that: The invention also includes designing a spaceborne array laser photon cloud data simulation method for ground laser angle reflection CCR, wherein the spaceborne array laser photon cloud data simulation method for ground laser angle reflection CCR includes: Calculates signal radiation scattered from corner reflectors, including: Considering the form of laser Gaussian beam distribution, the CCR echo photon is expressed as: （17） In formula (17), δ(θ) is the scattering cross-sectional area of ​​the corner reflector, and δ(θ) is expressed as: （18） In formula (18), is the normalized light intensity distribution, J1() is the first-order Bessel function, θ is the diffraction angle, r is the CCR aperture radius, is the peak cross-sectional area of ​​far-field light intensity, Expressed as: （19） In formula (19), ρ is the reflectivity of the coated CCR, the reflectivity of the aluminum-coated CCR is 0.78, and D = 2r is the CCR aperture diameter; According to Fraunhofer diffraction theory, the far-field normalized light amplitude of CCR is obtained: （20） In formula (20), r is the radius of CCR; is the normalized polarization complex amplitude of the nth part, for the coated CCR ; k is the wave number equal to , is the laser wavelength; , ; θ0 is the angle between the outgoing beam and the incident light. If the three dihedral angle errors of CCR are equal to β, , n refractive index is 1.46; and are the polar coordinates in the CCR coordinate system and the polar coordinates of the far-field diffraction point P, , θ is the diffraction angle, is the azimuth angle of the diffraction point P; Simplifying Equation (20) yields the analytical solution of the CCR far-field normalized amplitude: （21） In formula (21), is a first-order Bessel function, and the remaining parameters in Equation (21) are expressed as: ； According to the relationship between amplitude and light intensity, the far-field light intensity distribution of CCR reflection can be obtained as: （22） The average normalized intensity on the diffraction angle θ ring is: （23） Since the satellite platform moves at high speed in space, when the CCR echo beam is reflected to the position where the laser pulse is emitted, the satellite position deviates from the beam direction by a velocity difference angle. The calculation formula of the velocity difference angle is: （24） In formula (24), Re is the radius of the Earth (6370 km), is the acceleration due to gravity, H is the satellite orbit height, and z is the zenith angle; When the satellite-borne laser altimeter uses nadir measurement, the velocity difference angle is approximately: （25） Satellite is located The number of photons that can be received at is: （26） In formula (26), x c with y c is the CCR coordinate; For spaceborne lidar, when the emitted laser pulse is Gaussian and the detection target is a linear single target, the received signal according to diffraction theory can be simplified to Equation (26): （27） In formula (27), Ns is the average number of received photons. The Ns of the two types of objects are expressed by formula (13) and formula (26) respectively; is the RMS pulse width of the received signal, Expressed using formula (28): （28） In formula (28), Expressed as the RMS pulse width of the transmitted pulse, is the surface roughness, and are the surface slopes in the along-track and perpendicular-track directions, c is the speed of light, θ T is the laser divergence angle.

6. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 2, characterized in that: The method for constructing the single-photon detector response model in step S23 includes: The pulse waveform S(t) is collected and recorded after reaching the altimeter. The impulse response function of the altimeter is: （31） In formula (31), IRF is the impulse response function, is the number of statistical frames along the track, is the upward rounding function; IRF calculation is divided into two directions: the photon number statistics along the track and the elevation direction. is the step size of each statistical box along the track, is the total along-track statistical time; After determining the range of each along-track statistical frame, the photon point cloud within the range is statistically histogramed according to the elevation with a step size of , For the The backscatter signal value of each elevation statistical box. The box where the peak backscatter signal is located is set to the elevation position of the ground surface by default and is set to p. is the range of the impulse response function, where and Customize the required Surfu above the surface, Surfd below the surface, and elevation statistics step to obtain; The total number of elevation statistics frames is n+m+1; Combined with the receiving system's receiving efficiency , the photoelectric conversion quantum efficiency of the detector After the pulse response function is calculated, the laser signal and the system background noise are combined and convolved with the pulse response function to obtain the altimeter receiving echo of the entire single-photon laser altimeter system: （32） In formula (32), is the echo received by the entire single-photon laser altimeter system, is the signal echo, is the solar background noise, is the dark count noise, and the noise is integrated into ; After passing through the filter, the laser is further transmitted to the single-photon detector. Detected in time slots The probability of a photon is expressed using a Poisson distribution: （33） The laser is detected by the detector after passing through the atmospheric end flow, which includes two random processes: atmospheric turbulence and detector Poisson detection. The random process of atmospheric turbulence affecting photons will affect the parameter N in the Poisson random process of detector detection of photons. The probability density of detector detection after the laser passes through atmospheric turbulence is obtained from the Mandel formula: （34） The probability that no photon detection occurs in a single time slot is: （35） The detection of a photon in a single time slot is complementary to the absence of a photon detection event in a single time slot. The probability of detecting a photon in a single time slot is: （36） Considering the influence of the dead zone, the detection probability of a single-photon detector in the i-th time slot is the probability that no photon detection occurs during the duration of the dead zone and the probability that the i-th time slot is detected when the dead zone is not considered: （37）。 7. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 1, characterized in that: The method for evaluating the quality of spaceborne array laser simulation data under different configuration parameter conditions includes: S31. Calculate the photon point cloud noise rate, where the point cloud noise rate is defined as the number of noise photon events recorded by a single pixel of the array laser altimeter per unit time: （38） In formula (38), is the noise rate defined in this paper, The number of noises recorded from 50 detections of a single pixel; is the window height, It is the total number of photons in 50 beams minus the noise obtained by the signal identified by the built-in filtering algorithm. is the speed of light; S32. Calculate the average signal photon number. The average signal photon number is defined as the average number of signal photon events recorded by a single detection of a single pixel: （39） In formula (39), is the average number of signal photons, The total number of signal photons recorded by 50 detections of a single pixel; S33. Calculate the detection probability. The detection probability is defined as the probability that a single pixel can detect a target in a single detection: （40） In formula (39), represents the detection probability, Indicates the number of signal photons recorded in 50 detections; S34. Calculate the signal-to-noise ratio. Define the signal-to-noise ratio of altimetry data as the logarithm of the ratio of the number of signal photons to the number of noise within a 1-meter elevation range: （41） In formula (41), SNR is the point cloud signal-to-noise ratio, is the number of noises within the range, .

8. The method for comprehensive simulation of three-dimensional terrain mapping data using a spaceborne array laser radar according to claim 3, characterized in that: The method for solving the object space three-dimensional coordinates corresponding to the array laser detection pixel in step S11 includes: calculating the two-dimensional coordinates and pixel pointing vector of the laser detector detection pixel in the array laser radar coordinate system according to the altimeter parameters, combining the satellite attitude and orbit parameters, and intersecting with the ground reference terrain to calculate the object space three-dimensional coordinates, using atmospheric pressure, temperature, and humidity parameters to calculate the atmospheric refraction correction number to obtain actual distance information, solving the object space three-dimensional coordinates based on the geometric model of the satellite-borne array laser altimeter, and comprehensively considering the influence of tidal correction and aberration to obtain the object space three-dimensional coordinates with additional offset.

9. A system for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array laser radar, for implementing the method for comprehensively simulating and emulating three-dimensional terrain mapping data of a space-borne array laser radar according to any one of claims 1 to 8, characterized in that: include: Spaceborne single-photon array laser altimeter simulation link subsystem: used to establish a spaceborne single-photon array laser altimeter simulation link; Comprehensive simulation model construction subsystem: used to build a comprehensive simulation model of space-borne lasers and generate space-borne array laser simulation data sets; Array laser data quality evaluation subsystem: It is used to evaluate the quality of spaceborne array laser simulation data under different configuration parameters using multiple evaluation indicators such as noise rate, average number of signal photons, detection probability, signal-to-noise ratio, and elevation accuracy.

10. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method for comprehensive simulation of three-dimensional terrain surveying and mapping data of a space-borne array lidar are implemented as described in any one of claims 1-8.

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