Method and system for measuring time delay of satellite laser ranging system based on space target

Abstract

The invention discloses a method and system for measuring the time delay of a satellite laser ranging system based on a space target, relates to the technical field of laser ranging, and aims to measure the time delay of the system by using a geostationary satellite with a stable orbit and a long distance as a space target. According to the method, the influence of error sources such as a ground observation system, a space transmission link and an observation target on the time delay of the laser ranging system is fully considered. By implementing the dynamic observation process, the problem that a static ground target can only obtain the system time delay under the pointing of a single telescope is solved, and the common obvious difference between an actual observation condition and an ideal setting condition is overcome, so that the accuracy of a laser ranging result is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging, and in particular to a method and system for measuring the time delay of a satellite laser ranging system based on a spatial target. Background Art

[0002] Satellite Laser Ranging (SLR) technology calculates the precise distance between a target and an observation site by accurately measuring the round-trip time of a laser pulse from a ground observation point to a satellite. As one of the currently most accurate geodetic space measurement technologies, SLR technology has been widely applied in aspects such as precise satellite orbit determination, determination of Earth rotation parameters, establishment and maintenance of the Earth reference frame, and realization of global high-precision time transfer.

[0003] With continuous breakthroughs in the application scope (interplanetary) and measurement accuracy (millimeter level) of SLR technology, the application fields have expanded rapidly, and the requirement for data stability has been increasing day by day. For example, the Global Geodetic Observing System (GGOS) integrates various geodetic observation means and technical methods (SLR / VLBI / GNSS / DORIS), and requires the data stability of SLR stations to reach 0.1 mm / year. Currently, the data stability of most SLR stations is at the centimeter level, which still cannot meet the requirements of GGOS, restricting the application of SLR technology with millimeter-level measurement accuracy. The International Laser Ranging Service (ILRS) has taken improving data stability as one of the key directions for future development and research of SLR technology, and this topic has become a fixed issue in recent ILRS conferences. At the same time, the ILRS plans to improve the international standard of existing data stability to meet the needs of technological development.

[0004] The external consistency accuracy of SLR data is one of the important indicators for evaluating ranging results. The external consistency accuracy refers to the deviation between the measured value and the true value of the distance between the satellite and the station, mainly depending on the accuracy of the system time delay calibration. The SLR raw data records the time interval between the start pulse generated by the main wave probe and the closing signal obtained by the echo detector, while in actual applications, the ground time needs to be reduced to the telescope phase center (the intersection of the horizontal and vertical axes of the telescope). Since the two detection points do not coincide with the phase center of the instrument, a system path time delay is generated. As Figure 1 described, the composition and time delay distribution of the SLR system. According to the classification of error sources, the SLR system time delay is mainly divided into the optical path time delay dr optical , the electronic time delay dr electronical . Among them, the optical path time delay dr optical is:

[0005] dr o =de 2 -de 1 +dr1

[0006] In the above formula, de1 is the optical path time delay from the beam splitter to the phase center of the telescope, de2 is the sum of the optical path time delay in the beam splitter and the optical path time delay from the beam splitter to the main wave detector, and dr1 is the optical path time delay from the phase center of the telescope to the detection surface of the echo detector.

[0007] The electronic time delay dr electronical is:

[0008] dr o = de 3 + de 4 + dr 2 + dr 3

[0009] where de3 is the internal time delay of the main wave detector; de4 is the electrical signal time delay from the signal output end of the main wave detector to the event timer end; dr2 is the internal time delay of the echo detector; dr3 is the electrical signal time delay from the output end of the echo detector to the event timer end. It can be seen that dr electronical is a variable, related to factors such as the response time of the electronic device, the cable length, and the cable connectors, and changes with the working state of the electronic device.

[0010] Prior art one:

[0011] Ground target measurement is an important means for the time delay calibration of the existing SLR system. The numerical accuracy and stability of ground target measurement directly affect the data quality of SLR. In ground target measurement, by emitting laser to a ground target at a fixed distance and receiving the echo signal, the system time delay is obtained using the time difference between the transmitted and echo signals. According to the distance between the ground target and the ranging system, ground target measurement is divided into near ground target and far ground target. Among them, the observation distance of the far ground target is 10 - 10000 m. Due to the relatively long transmission distance, the influence of atmospheric error needs to be considered, and the ranging value needs to be corrected for atmospheric delay. For far ground target measurement, empirical formulas are often used in the field of laser ranging at home and abroad for atmospheric delay correction. The formula is as follows:

[0012]

[0013] In the formula, △R is the distance correction value; R is the ground target ranging value; P is the atmospheric pressure at the measurement station (mbar); T is the temperature value at the measurement station (°C).

[0014] The formula for calculating the system delay of the far ground target is:

[0015] ΔD = R d - D - ΔR;

[0016] Among them, the distance from the reference point of the SLR station to the ground target is D, which can be accurately measured by devices such as high-precision total stations at the millimeter or sub-millimeter level. Rd is the average measured value of the ground target measurement.

[0017] Disadvantages of the prior art I:

[0018] For remote ground target measurement, due to the relatively long distance of the measurement object, the influence of atmospheric factors on the measurement results must be fully considered. Factors such as temperature, humidity, and air pressure in the atmosphere will cause refraction and delay of the optical signal during propagation, resulting in distance errors. Although atmospheric delay correction formulas can be used to estimate these errors, the actual observation conditions often differ significantly from the ideal set conditions, leading to doubts about the accuracy of the correction results. In addition, environmental factors have a certain degree of uncertainty and real-time nature, which makes the measurement results at different times and locations may have large fluctuations, affecting the reliability of the data.

[0019] The SLR system is an all-sky observation, and the optical path time delay generated by the transmitting and receiving systems is related to the telescope pointing. Remote ground target measurement is a static target, which can only measure in a specific direction and cannot accurately reflect the time delay changes of the telescope at different pointings, limiting its practical application.

[0020] The remote ground target is at a relatively long distance from the ranging system, making it difficult to maintain and also difficult to aim during measurement.

[0021] Prior art II:

[0022] The near-ground target is currently the main method for most laser ranging stations to obtain the system time delay. The near-ground target is usually placed inside a dome, about 1 - 3 m away from the telescope. It is less affected by meteorological parameters and does not require meteorological correction, eliminating the errors caused by the uncertainty of meteorological correction. The near-ground target usually uses two reflecting plates for refraction to attenuate the emitted laser and then return it to the receiving system. By measuring the time difference between the emitted and echo signals, near-ground target data is obtained. The average value of the measured near-ground target data minus the known distance value is the system correction value. The known distance of the near-ground target can be manually measured with an ordinary steel tape to obtain the true distance of the near-ground target, with an accuracy of within 3 mm, and it is simple and easy to operate, avoiding the error of the true distance of the ground target caused by problems with the rangefinder. Since the near-ground target is inside the movable dome, tests can be carried out during the day, saving the system debugging time. Figure 2 It is a schematic diagram of near-ground target correction. Among them, M1 and M2 are the near-ground target reflectors.

[0023] Disadvantages of the prior art II:

[0024] During the measurement of the near-earth target, the laser attenuation technology is adopted to control the echo intensity. However, due to the short distance between the near-earth target and the telescope system, the echo intensity is still much greater than the actual satellite laser ranging echo intensity. The SLR system uses a single-photon detector, and multi-photon echoes are extremely likely to cause damage to the device and introduce additional measurement errors, resulting in inaccurate determination of the system time delay.

[0025] The near-earth target is a static target and cannot accurately reflect the time delay changes of the telescope at different pointing directions, which limits its accuracy in practical applications.

[0026] The SLR system observes according to the satellite prediction, and there are obvious differences between its observation time and the ground target measurement time. The electronic time delay in the SLR system changes with the working time of the system, affecting the accuracy of the measurement results.

[0027] During the measurement of the near-earth target, the elevation angle of the telescope needs to be reduced from the observation angle to 0 degrees to accurately point the telescope system at the near-earth target. For telescopes with a large aperture, due to their own weight and structural characteristics, they are extremely likely to shake, resulting in pointing errors and reducing the system time delay accuracy.

[0028] Existing technology three:

[0029] The one-way system delay measures the time delay of the laser ranging transmitting system and the receiving system respectively through the one-way delay calibration device. The one-way delay calibration device consists of an event timer, a photodetector PD, a transmission optical path, cables, interfaces, and other accessories. By forming a closed loop with the transmitting part and the receiving part of the laser ranging system respectively, the calibration of the transmitting time delay and the receiving time delay can be completed. Figure 3 It is a schematic diagram of the structure of the laser ranging transmitting time delay calibration system. It includes a laser transmitting end and a one-way delay calibration device. The laser ranging transmitting end consists of a laser, a main wave detector, a coudé transmitting system, a high-frequency coaxial cable, etc. The transmitting end and the one-way delay calibration device share an event timer.

[0030] At the transmitting end, each moment is recorded according to its own time system. t tran represents the moment when the signal pulse passes through the transmitting reference point, and t e represents the moment of the signal pulse recorded by the time system at the transmitting end. The difference τ 1 =t e -t tran is called the delay amount at the transmitting end and can be expressed as:

[0031] τ 1 =t rpd2 -t e -t epd2 -t pd2 -t l3 -tothers

[0032] In the formula, t rpd2 and t e are the moments recorded by the event timer in response to the output signals of two photodetectors PD and PD 2 respectively; t epd2 is the time delay of the optical signal from point E to the photosensitive element target surface of the photodetector PD 2 ; t pd2 is the time delay of the photodetector PD 2 ; t l3 is the transmission time delay of the signal in the cable l 3 ; t others is the sum of the time delays of the signal converter and the adapter added by adjusting the positive and negative of the signal and the cable connection method.

[0033] Figure 4 is a schematic structural diagram of a laser ranging receiving time delay calibration system. It includes a laser receiving end, a fixed-distance ground target, and a one-way delay calibration device. The laser receiving end consists of a Cassegrain receiving system, a single-photon detector SPAD, a high-frequency coaxial cable, etc.; the fixed-distance ground target consists of two wedge mirrors and a bracket.

[0034] The signal pulse passes through t fly the flight time and reaches the receiving reference point from the transmitting reference point. t rec represents the moment when the signal pulse passes through the receiving reference point, and t r represents the moment of the signal pulse recorded by the receiving end time system. The receiving time delay τ 2 is the difference between the two, τ 2 =t rec -t r , and can be expressed as:

[0035] τ 2 =t r -t spa2 -t IH -t IF +t H +t HB +t pd2 +t l3 +t others

[0036] In the formula, t r and t spa2 are the moments recorded by the event timer in response to the output signals of the photodetector PD 2 and the single-photon detector SPAD respectively; t H is the time delay of the optical signal in the wedge mirror at point H; t HB is the distance from the rear surface of the wedge mirror at point H to the photodetector PD 2Time delay of the photosensitive element target surface; t IH and t IF is the optical path time delay.

[0037] During the above measurement process, it should be noted that it is necessary to ensure that the time interval t rpd2 -t e and t r -t spa2 is greater than the dead time of the event timer.

[0038] Disadvantages of the prior art three:

[0039] The prior art has complex operations and poor real-time performance, seriously affecting the system working efficiency and being not conducive to routine observations.

[0040] The equipment calibration process of the prior art is cumbersome and requires frequent manual intervention, which not only increases the work intensity of the operators but also easily introduces human errors, affecting the accuracy of the measurement results.

[0041] The prior art is based on measurements under static conditions and lacks the real-time response ability to dynamic changes, and may not be able to adapt to rapidly changing measurement environments.

[0042] The prior art forms a calibration system through cables and photodetectors, and there may be systematic errors, such as non-linearity of equipment, inaccurate calibration, etc. These errors reduce the accuracy of one-way delay calibration.

[0043] Explanation of key terms and introduction of technical abbreviations:

[0044] 1. Laser ranging: Laser ranging is mainly achieved based on the time-of-flight principle. The common pulsed laser ranging indirectly determines the calculated distance by directly measuring the time interval between the transmitted beam and the received beam.

[0045] 2. According to different observation targets, laser ranging systems are divided into Satellite Laser Ranging (SLR), Debris Laser Ranging (DLR), Lunar Laser Ranging (LLR), etc.

[0046] 3. Relativistic error: When a laser beam propagates in different reference frames, due to relativistic effects, the measured time and distance may be different. For example, if the relative speed between the laser rangefinder and the target object is close to the speed of light, the propagation time of the laser signal will be affected by relativistic effects, resulting in deviations in the measurement results.

[0047] 4. Atmospheric transmission error: The measurement error caused by effects such as atmospheric refraction, scattering, absorption, and turbulence when the laser signal propagates in the atmosphere.

[0048] 5. Satellite shape effect error: The measurement error caused by the shape and attitude of the satellite itself.

[0049] 6. External consistency accuracy of laser ranging data: The deviation between the measured value and the true value of the distance between the space target and the measuring station.

[0050] 7. Total station: A high-precision measuring device that integrates the functions of an electronic distance meter (EDM) and an optical theodolite, and is widely used in engineering surveying, construction, topographic surveying, mine surveying, and other fields that require precise measurement. It can synchronously measure the horizontal angle, vertical angle, and inclined distance, and then accurately calculate the three-dimensional coordinates.

[0051] 8. Lidar equation:

[0052]

[0053] Where E is the single-pulse energy of the laser; λ is the laser pulse wavelength; h is Planck's constant; c is the speed of light in vacuum; A s is the effective area of the reflector on the satellite; A r is the effective area of the receiving mirror; K t is the efficiency of the transmitting system; K r is the efficiency of the receiving optical system; T is the one-way atmospheric transmittance; β is the attenuation efficiency; R is the inclined distance from the measuring station to the satellite; θ t is the laser beam divergence angle (after passing through the divergence mirror); θ s is the beam divergence angle of the satellite reflector.

[0054] 9. Due to the orbital error in satellite prediction, the slant range residual caused by the predicted orbital error consists of two parts: the distance deviation RB and the time deviation TB, Δp = RB + Tb * Ran. Ran is the projection of the satellite speed at time ti in the direction of the p vector. Summary of the Invention

[0055] The technical solution of the present invention to solve the above technical problems is to provide a method for measuring the time delay of a satellite laser ranging system based on a space target, including the following steps:

[0056] Direct the telescope to the target satellite according to the space target prediction,

[0057] Control the laser to emit, generate a range gate signal, and control the single-photon detector to turn on; at the same time, the PIN obtains the main wave emission signal, which is transmitted to the event timer interface through the cable to obtain the precise time t of laser emission 1 ;

[0058] The echo signal returned by the target satellite is converged by the telescope echo receiving system, passes through the field stop and the narrowband filter, reaches the C-SPAD target surface, and then undergoes photoelectric conversion. The arrival time t′ of the echo is recorded by the event timer. 1 。

[0059] Pair the two-channel times recorded by the event timer to obtain the precise time and the arrival time; the difference between the two times is the observed time interval Δt from the ground target to the measuring station. o =t′ 1 -t 1 ;

[0060] Store the observation time, satellite distance, azimuth, and altitude in a file.

[0061] Obtain the local temperature, humidity, and air pressure parameters for distance correction.

[0062] Use the standard point algorithm to remove outliers and subtract the known distance value to obtain the system time delay value.

[0063] To solve the above technical problems, the present invention also proposes a satellite laser ranging system based on space target measurement for performing the method of satellite laser ranging system time delay based on space target measurement as described above. The system includes:

[0064] A laser emission module for emitting laser signals.

[0065] A space target module for reflecting echo signals.

[0066] A tracking and control module for laser emission control, range gate control, event timer control, time-frequency control, and servo system control.

[0067] An echo receiving module for receiving the optical pulse signal reflected by the space target and measuring the round-trip time of the laser pulse from the ground station to the satellite.

[0068] A time-frequency module for providing the absolute time coordinate for the operation of the system.

[0069] An information processing module for predicting and downloading the space target satellite, identifying and processing the space target echo signal, and obtaining the system time delay.

[0070] The present invention introduces an innovative method for calibrating the time delay of a spatial target measurement laser ranging system. Different from other existing time delay acquisition technologies, the present invention uses a geostationary satellite with a stable orbit and a relatively long distance as a spatial target to measure the time delay of the system. The method of the present invention fully considers the influence of error sources such as ground observation systems, space transmission links, and observation targets on the time delay of the laser ranging system. By implementing a dynamic observation process, the present invention solves the problem that a static ground target can only obtain the system time delay under the pointing of a single telescope, overcomes the significant differences that usually exist between the actual observation conditions and the ideal set conditions, and thus improves the accuracy of the laser ranging results.

[0071] Compared with the existing technical solutions, the present application has the following beneficial effects:

[0072] Different from the prior art, the present invention uses a spatial target to obtain the time delay of a satellite laser ranging (SLR) system. By using the data of the geostationary satellite Lageos-1, the measuring station is connected to the global SLR network, ensuring the stability of the station coordinates and improving the accuracy of the reference coordinates of the system time delay.

[0073] Different from the prior art, the present invention uses Lageos-1 with good echo characteristics, a high and stable orbit as the target satellite, fully considers various error sources such as ground equipment, space environment, and target characteristics, ensures the consistency of the system time delay measurement and the satellite target measurement process, effectively reduces the errors caused by environmental changes, and improves the stability of the system time delay measurement.

[0074] Different from the prior art, the present invention uses Lageos-1 with a high orbit as the target satellite, ensuring the stability of the echo signal intensity of the system time delay measurement and avoiding the detection errors caused by multi-photon echoes of near-earth targets.

[0075] Different from the prior art, the present invention uses Lageos-1 with a stable orbit as a dynamic "spatial target", and through measurements at different times, different azimuths, and different elevation angles, realizes the precise calibration of the time delay of the laser ranging system in various measurement environments.

[0076] Different from the prior art, the present invention can conveniently and quickly calibrate the delay of the system through a standardized operation process, reducing the operation difficulty.

[0077] Different from the prior art, the present invention automatically realizes the system time delay measurement by formulating a reasonable observation strategy, reduces the manual intervention, and ensures the accuracy and stability of the measurement results. Description of the Drawings

[0078] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0079] Figure 1 It is the composition and delay distribution diagram of the SLR system;

[0080] Figure 2 It is the schematic diagram of near-earth target correction;

[0081] Figure 3 It is the schematic diagram of the emission delay structure of the laser ranging system;

[0082] Figure 4 It is the schematic diagram of the reception delay structure of the laser ranging system;

[0083] Figure 5 It is the schematic diagram of the structure of the satellite laser ranging system for space target measurement based on the present invention;

[0084] Figure 6 It is the flowchart of the operation of the satellite laser ranging system for space target measurement based on the present invention;

[0085] Figure 7 It is the distribution diagram of LAGEOS-1 satellite observation data;

[0086] Figure 8 It is the comparison diagram of the system delays obtained by measuring the ground target and the LAGEOS-1 satellite;

[0087] Figure 9 It is the residual scatter plot of LAGEOS2 on December 2, 2023;

[0088] Figure 10 It is the residual scatter plot of LAGEOS2 on December 3, 2023;

[0089] Figure 11 It is the residual scatter plot of LAGEOS2 on January 5, 2024;

[0090] Figure 12 It is the optical path structure of each subsystem of the transceiver-separated system.

[0091] Explanation of the reference numerals in the drawings: 1. Laser emission module, 2. Space target module, 3. Time and frequency module. 4. Echo reception module, 5. Tracking and control module, 6. Information processing module. Detailed implementation manners

[0092] The present invention provides a method and system for measuring the time delay of a satellite laser ranging system based on a space target, aiming to design a method for improving the accuracy of laser ranging results for a satellite laser ranging system based on a space target.

[0093] The method for measuring the time delay of a satellite laser ranging system based on a space target proposed by the present invention will be described in the following specific embodiments:

[0094] Embodiment 1:

[0095] A method for measuring the time delay of a satellite laser ranging system based on a space target includes the following steps:

[0096] According to the space target prediction, guide the telescope to point to the target satellite.

[0097] Control the laser to emit, generate a range gate signal, and control the single photon detector to turn on; at the same time, the PIN obtains the main wave emission signal, which is transmitted to the event timer interface through the cable to obtain the precise time t of laser emission. 1 ;

[0098] The echo signal returned by the target satellite is converged by the 60 cm telescope echo receiving system, and passes through the field stop and narrowband filter, reaches the C-SPAD target surface, and then undergoes photoelectric conversion. The event timer records the echo arrival time t'. 1 .

[0099] Pair the dual-channel times recorded by the event timer to obtain the precise time and the arrival time; the difference between the two times is the observed value time interval Δt from the ground target to the measuring station. o = t' 1 - t 1 ;

[0100] Store the observation time, satellite distance, azimuth, and altitude in a file.

[0101] Obtain the local temperature, humidity, and air pressure parameters for distance correction.

[0102] Adopt the standard point algorithm to remove outliers and subtract the known distance value to obtain the system time delay value.

[0103] Embodiment 2:

[0104] A satellite laser ranging system based on a space target is used to execute the method for measuring the time delay of a satellite laser ranging system based on a space target in Embodiment 1. As Figure 5 shown, the system includes:

[0105] A laser emission module for emitting laser signals.

[0106] A space target module for reflecting echo signals.

[0107] Tracking control module, used for laser emission control, range gate control, event timer control, time-frequency control and servo system control;

[0108] Echo receiving module, used for receiving the optical pulse signal reflected by the space target, and measuring the round-trip time of the laser pulse from the ground station to the satellite;

[0109] Time-frequency module, used to provide the absolute time coordinate for the operation of the system;

[0110] Information processing module, used for forecast downloading of the space target satellite, recognition and processing of the space target echo signal, and obtaining the system time delay.

[0111] The working process of the satellite laser ranging system based on space target measurement is as follows:

[0112] The time-frequency module downloads the satellite forecast according to the space target module;

[0113] The tracking control module synchronously tracks the satellite according to the observation target forecast downloaded by the information processing module, and sends instructions to the laser emission module;

[0114] The laser emission module emits a laser pulse to the space target module according to the instruction, and sends the main wave signal to the information processing module.

[0115] The echo receiving module records the main wave moment of the pulse according to the time information provided by the time-frequency module;

[0116] The tracking control module receives the echo signal returned by the observation target according to the door opening signal provided by the information processing module;

[0117] The tracking control module records the echo moment according to the time information provided by the time-frequency module;

[0118] The time-frequency module completes the pairing process according to the main echo data of the tracking control module, accurately measures the round-trip time t of the laser pulse from the ground station to the satellite, and performs data processing to obtain the system time delay.

[0119] Embodiment 3:

[0120] A method for the time delay of a satellite laser ranging system based on space target measurement, taking the Changchun Station transceiver-separated laser ranging system as an example, Figure 5It is a schematic diagram of a laser ranging system based on space target measurement. The parameters of the 60 cm SLR system are as follows: the transmitting telescope is 210 mm, the diameter of the receiving telescope is 600 mm; the single-pulse energy of the laser is about 1 mJ; the transmitting frequency is 1 KHz; the laser wavelength is 532 nm; the efficiency of the laser transmitting system is 0.6; the laser energy pulse width is 50 ps; the divergence angle of the transmitting beam is 11 arcseconds; the receiving efficiency is 0.5; the quantum efficiency of the receiving optoelectronic device is 0.2; the receiving field of view angle is 40 arcseconds; the distance gate width is 100 ns; the attenuation efficiency is -13 dB; the tracking error is 7 arcseconds (1σ); the ratio of the transmission band of the filter to the response band of the receiving optical system is 1 / 500. The space target satellite is Lageos-1.

[0121] As Figure 6 shown, it includes the following steps:

[0122] The ground equipment control machine issues a command signal, and according to the space target prediction (azimuth, altitude and distance), guides the telescope to point to the target satellite, so that the ranging system is in a standby state.

[0123] After the telescope points stably, control the laser to emit, generate a distance gate (Gate) signal, and control the opening of the single-photon detector (C-SPAD). At the same time, the PIN obtains the main wave emission signal, which is transmitted to the event timer interface by the cable to obtain the exact time of laser emission (referred to as the main wave emission time).

[0124] The echo signal returned by the target satellite is converged by the 60 cm telescope echo receiving system, and after passing through the field stop and narrowband filter, it reaches the C-SPAD target surface, and then after photoelectric conversion, the event timer records the echo arrival time.

[0125] The computer terminal pairs the two-channel times recorded by the event timer to obtain the original data obtained by the laser ranging system. The difference between the two times is the observed time interval from the ground target to the measuring station.

[0126] Store the observation time, satellite distance, azimuth and altitude into a file (the laser main wave time, the corresponding time interval, position information, but the position information is the state value of the telescope encoder near the time).

[0127] Read the meteorological measurement to obtain the local temperature, humidity and pressure parameters for distance correction.

[0128] The computer reads the above observation data, uses the standard point algorithm to remove outliers, and makes a difference from the known distance value to obtain the system time delay value.

[0129] LAGEOS-1 is a spherical satellite specifically designed for high-resolution geodynamics research and was successfully launched in May 1976. The satellite is small in size, high in density, low in surface-to-mass ratio, and has a relatively high orbital altitude. Therefore, it is less affected by various external disturbances, ensuring the stability of its orbit and high-precision orbit determination ability. LAGEOS-1 is not only the laser ranging satellite with the highest orbit determination accuracy and the most stable orbit currently, but also one of the satellites that have been most deeply studied. Since its launch, the observational data it has provided have produced important practical results in the field of geoscience research. In this invention, LAGEOS-1 is selected for the time delay of the space target measurement system.

[0130] Figure 7 Shows the distribution of the measurement data of the LAGEOS-1 satellite at Changchun Station on the celestial sphere between December 1, 2023 and January 5, 2024. There are a total of 81 orbits of data. It can be seen that the observational data are relatively evenly distributed on the celestial sphere, which effectively solves the problem that the existing ground target technology can only obtain the system time delay in a single direction. In the figure, the azimuth 0 point is due north, and the arc is caused by avoiding the dome.

[0131] Figure 8 Are the system delay measurement values of the 60 cm telescope at Changchun Station obtained by measuring the ground target and the space target. The maximum system delay obtained by measuring the ground target is 184231 ps, and the minimum is 183865 ps; the maximum system delay obtained by measuring the LAGEOS-1 satellite is 184743 ps, and the minimum is 182747 ps. The maximum standard deviation of the measurement results is 251 ps, and the minimum is 22 ps. Compared with the ground target results, the RMS value is 470 ps. It can be seen that the RMS of the space target is larger because the space target comprehensively considers the effects of various error sources such as the atmosphere, the satellite, and the telescope pointing on the system time delay, and can more comprehensively reflect the actual changes in the system time delay, providing an important reference for improving the system measurement accuracy.

[0132] On December 2 and 3, 2023 and January 5, 2024, satellite laser ranging data were processed based on the space target system time delay data. LAGEOS-2 was selected as the observation target to verify the applicability and accuracy of this embodiment. The residual scatter plots of LAGEOS-2 on December 2, 2023, December 3, 2023, and January 5, 2024 are as Figure 9 、 Figure 10 、 Figure 11 shown.

[0133] Using the space target and ground target data, combined with the orbit prediction data, the range deviation of the LAGEOS-2 satellite was calculated, as shown in Table 1. It can be seen that the range deviation obtained based on the space target data is significantly reduced, which is of great importance for the precise observation of the satellite.

[0134] Table 1:

[0135] Ground target (mm) Space target (mm) 1 -37.0 -10.7 2 -86.0 -48.6 3 9.0 -1.8

[0136] In order to further verify the applicability of the space target to laser ranging, based on the above data, the least squares method was used to process the LAGEOS-2 observation data. Table 2 shows that the processing accuracy of the satellite observation data processed using the space target data has been significantly improved, and the residuals of the LAGEOS-2 observation data have been significantly reduced.

[0137] Table 2 Comparison of the measurement residuals RMS between the space target and the ground target:

[0138]

[0139] Example 4:

[0140] Taking the space debris laser ranging system with separate transmitting and receiving telescopes composed of the 1.56m aperture astronomical telescope and the 60cm aperture laser ranging telescope of the Shanghai Astronomical Observatory as an example, the two are 55m apart. Among them, the 60cm aperture laser ranging telescope is the transmitting telescope, which also receives the echo signal while transmitting the laser signal. The receiving aperture 1.56m telescope is the receiving telescope, responsible for receiving the echo signal. The specific parameters are as follows:

[0141] Table 3. 1.56-meter telescope system and 60cm telescope system:

[0142]

[0143]

[0144] Different from Example 3, in this example, Link 2 (ultra-near-earth target) will no longer use the mirror mounted on the truss of the receiving telescope, but use optical fibers to change the propagation path of the optical signal, effectively forwarding the laser signal from the transmitting optical path to the receiving optical path, and then obtaining the overall system delay.

[0145] Example 5:

[0146] Taking the space debris laser ranging system with separate transmitting and receiving telescopes composed of the 1.2m aperture 10Hz common-path laser ranging system and the 53cm binocular telescope 1kHz SLR astronomical telescope of the Yunnan Astronomical Observatory as an example, the two are 55m apart. Among them, the 50cm aperture SLR telescope is the transmitting telescope, which also receives the echo signal while transmitting the laser signal. The receiving aperture 1.2m telescope is the receiving telescope, responsible for receiving the echo signal. The optical path diagram of the telescope is as Figure 12 shown, where a is the laser ranging transmitting / receiving optical path of the 53cm binocular telescope, and b is the receiving optical path of the 1.2m telescope.

[0147] Different from Embodiment 3, in this embodiment, Link 3 (the target satellite) will select the geostationary satellite LAGEOS-1, and use LAGEOS-2 to obtain the overall system delay.

[0148] It should be noted that:

[0149] The target satellites adopted by the present invention can be LAGEOS-1, LAGEOS-2, etc., and the geostationary orbit satellites are not unique.

[0150] The laser ranging systems applicable to the present invention can be satellite laser ranging systems, space debris laser ranging systems, lunar laser ranging systems, etc.

[0151] The data processing methods adopted by the present invention can be the average weight method, the least square method, and the data processing methods are not unique.

[0152] The observation strategies of the present invention can adopt manual discrimination and automatic processing, and the system delay task selection methods are not unique.

[0153] In the separated transceiver laser ranging system applicable to the present invention, the optical telescope system can be a separated transceiver or a coaxial transceiver system, and the selection of the telescope system is not unique.

[0154] The laser sources in the laser ranging systems applicable to the present invention can be selected from 532nm, 1064nm, 1550nm, etc., and the applicable wavelengths are not unique.

[0155] The laser repetition frequencies adopted in the laser ranging systems applicable to the present invention are 1KHz, 2KHz, 100KHz, etc., and the laser repetition frequencies are not unique.

[0156] The apertures of the optical telescope systems in the laser ranging systems applicable to the present invention can be 60cm, 120cm, 250cm, and the telescope apertures are not unique.

[0157] The receiving detectors in the laser ranging systems applicable to the present invention can be APD, PMT, SNSPD, etc., and the selection of the detectors is not unique.

[0158] As mentioned above, only the preferred specific embodiments of the present invention are described, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for measuring the time delay of a satellite laser ranging system based on a space target, characterized in that: The following steps are involved: Guide the telescope to the target satellite according to the space target prediction; Control the laser emission, generate the range gate signal, and control the single photon detector to turn on; at the same time, the PIN obtains the main wave emission signal, transmits it to the event timer, and obtains the precise time t1 of the laser emission; The echo signal returned by the target satellite is collected by the telescope echo receiving system, and passes through the field of view aperture and narrow-band filter to reach the C-SPAD target surface, and then undergoes photoelectric conversion, and the echo is recorded by the event timer. Arrival time t1; Pair the dual-channel times recorded by the event timer to obtain the precise time t1 and the arrival time" t1; the difference between the two times is the observation time interval Δt from the ground target to the measuring station o =t1-t1; Store the observation time, satellite distance, azimuth and altitude into a file; Obtain local temperature, humidity, and air pressure parameters for distance correction; The standard point algorithm is used to remove outliers and the system delay value is obtained by subtracting the known distance value.

2. A satellite laser ranging system based on space target measurement, characterized in that: The method for measuring the time delay of a satellite laser ranging system based on a space target according to claim 1, the system comprising: A laser emission module, used for emitting laser signals; A space target module, used to reflect the echo signal; Tracking control module, used for laser emission control, range gate control, event timer control, time and frequency control and servo system control; The echo receiving module is used to receive the optical pulse signal reflected from the space target and measure the round-trip time of the laser pulse from the ground station to the satellite; The time frequency module is used to provide the absolute time coordinates of the system's operation; The information processing module is used for downloading forecasts of space target satellites, identifying and processing space target echo signals, and obtaining system delays.

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