Two-dimensional lookup table acquisition method and device for slice segmentation of spaceborne microwave scatterometer

Abstract

The present application belongs to the field of active microwave remote sensing and microwave scatterometer, and particularly relates to a kind of two-dimensional look-up table acquisition methods of spaceborne microwave scatterometer slice segmentation, the method comprises: obtaining the three-dimensional distribution of Doppler frequency offset with satellite platform subsatellite point latitude, azimuth and pitch;And based on the three-dimensional distribution, obtain Doppler frequency offset;Again, using the relationship between echo frequency and Doppler frequency offset of spaceborne sector-beam conical scanning microwave scatterometer, obtain the three-dimensional distribution of echo frequency of spaceborne sector-beam conical scanning microwave scatterometer with satellite platform subsatellite point latitude, azimuth and pitch;With equidistant ground slice as target, obtain the position of equidistant ground slice on the echo frequency corresponding to pulse sampling point, obtain the three-dimensional look-up table of slice segmentation;Dimension reduction optimization is carried out to three-dimensional segmentation look-up table, and two-dimensional look-up table of spaceborne sector-beam conical scanning microwave scatterometer slice segmentation is obtained.

Description

Technical Field

[0001] This invention belongs to the field of active microwave remote sensing and microwave scatterometer technology. Specifically, it relates to a method and apparatus for obtaining a two-dimensional lookup table for segmentation of spaceborne microwave scatterometer slices. Background Technology

[0002] Sea surface wind field is an important physical parameter in marine and atmospheric science research and applications. As the most important remote sensing instrument for acquiring global sea surface wind field data, the spaceborne microwave scatterometer plays a vital role in numerical weather prediction, marine disaster monitoring, marine environmental numerical forecasting, meteorological forecasting, and climate research.

[0003] Spaceborne microwave scatterometers can be categorized into three different types: pencil-beam conical scanning microwave scatterometers, fixed sector-beam microwave scatterometers, and sector-beam conical scanning microwave scatterometers. Pencil-beam conical scanning scatterometers typically employ two conical beams (inner and outer) for Earth observation, with the pulse beam's footprint on the ground typically spanning tens of kilometers in both azimuth and elevation. Fixed sector-beam scatterometers are usually equipped with several antennas at fixed observation azimuths to observe the Earth's surface.

[0004] The fan-beam conical scanning microwave scatterometer is a new beam system proposed by the European Space Agency (ESA). It combines the large footprint of a fixed fan-beam scatterometer with the rotating scanning capability of a pencil-beam scatterometer, significantly increasing the number of repeated observations of wind elements within the sweep area while reducing the antenna rotation rate. The pulse beam of the fan-beam conical scanning microwave scatterometer typically leaves a footprint on the ground at an elevation angle of several hundred kilometers, while the fan-beam antenna rotates at a certain speed, achieving multi-azimuth observations of the target and complete coverage of the observation area.

[0005] Spaceborne scatterometer pulse observation footprints typically range from tens to hundreds of kilometers. Range-gating reconstruction of pulse sampling points within the observation footprint is usually required to obtain observation slices with a specific resolution. Since spaceborne scatterometers are primarily used to observe large-scale targets such as the ocean, the elevation observation slice scale is generally on the order of kilometers. Pencil beam scatterometers, due to their narrow beams (e.g., the SeaWinds inner and outer beamwidths in the elevation direction are 1.6° and 1.4°, respectively, and the azimuth beamwidths are 1.8° and 1.7°, respectively), exhibit relatively small elevation Doppler frequency variations. After Doppler frequency compensation, the echo frequency has an approximately linear relationship with the observation slant range, and equal-frequency division of the footprint pulse sampling points is usually sufficient. In contrast, fan-beam rotating scanning scatterometers, because the azimuth angles of each beam antenna remain constant, do not require consideration of the Doppler frequency variation in the azimuth direction when segmenting elevation observation slices, making it easy to achieve slice segmentation with a fixed azimuth angle.

[0006] This invention primarily addresses the problem of pulse footprint slice segmentation in a fan-beam conic scatterometer. Because the Doppler frequency offset of a fan-beam conic scatterometer is distributed in three dimensions (latitude, azimuth, and elevation) along with the nadir point on the satellite platform, its echo frequency also exhibits a three-dimensional distribution along these dimensions. This makes the correspondence between echo frequency and observation slant range quite complex. The pulse footprint slice segmentation for a fan-beam conic scatterometer, under the condition of echo frequency distribution along the three-dimensional dimensions of the nadir point, optimizes the approximate equal interval of ground footprint slices by using a lookup table to represent the slice accumulation process of pulse sampling points. The equal-frequency partitioning method commonly used in microwave scatterometers cannot be applied to the slice segmentation of a fan-beam conic scatterometer. This invention uses a lookup table to achieve real-time on-board slice segmentation. However, three-dimensional lookup tables require high on-board resources and computational efficiency, and obtaining real-time nadir point latitude information during on-board processing is difficult. Therefore, this invention optimizes the dimensionality of the three-dimensional lookup table for slice segmentation. While ensuring that the ground footprint slices are approximately equally spaced, the three-dimensional lookup table for slice segmentation of different sub-satellite latitude intervals, azimuth intervals, and pitch intervals is transformed into a two-dimensional lookup table for slice segmentation of different azimuth intervals and pitch intervals. Summary of the Invention

[0007] To address the aforementioned deficiencies in existing technologies, this invention proposes a two-dimensional lookup table acquisition method for slice segmentation of a fan-beam conical scanning microwave scatterometer. The Doppler frequency of the spaceborne scatterometer is three-dimensionally coupled in latitude, azimuth, and elevation directions at the nadir point; its echo frequency is also three-dimensionally coupled in latitude, azimuth, and elevation.

[0008] This invention provides a method for obtaining a two-dimensional lookup table for slice segmentation of a spaceborne microwave scatterometer, the method comprising:

[0009] Based on the conical scanning observation geometry of the spaceborne fan-beam microwave scatterometer, and combined with the relative motion between the satellite platform and the Earth, the three-dimensional distribution of the Doppler frequency shift with the latitude, azimuth, and pitch of the satellite platform's nadir point is obtained; based on the current latitude, azimuth, and pitch of the satellite station's nadir point, the obtained three-dimensional distribution is used to obtain the Doppler frequency shift.

[0010] Based on the Doppler frequency offset, the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer is obtained by using the relationship between the echo frequency and the Doppler frequency offset. Then, the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with the latitude, azimuth and elevation of the satellite station's nadir point is obtained.

[0011] Based on the three-dimensional distribution of the echo frequency of the spaceborne fan-beam scanning microwave scatterometer with the latitude, azimuth and elevation of the satellite station's nadir point, and taking equally spaced ground slices as targets, the position of the equally spaced ground slices at the echo frequency corresponding to the pulse sampling point is obtained, and a three-dimensional lookup table for slice segmentation is obtained.

[0012] Then, using equally spaced ground slices as the optimization target, the three-dimensional segmentation lookup table is optimized by dimensionality reduction to obtain a two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer.

[0013] As one improvement to the above technical solution, the three-dimensional distribution of the Doppler frequency shift with the latitude, azimuth, and pitch of the satellite platform's nadir point is obtained based on the conical scanning observation geometry of the spaceborne fan-beam microwave scatterometer and the relative motion between the satellite platform and the Earth; the specific process is as follows:

[0014] Assume r sat (γ,ψ) and v sat (γ,ψ) represents the position and velocity vectors of the satellite platform in the Earth-fixed coordinate system; This is the position vector of the ground observation target in the Earth-fixed coordinate system;

[0015] Where γ and ψ are the longitude and latitude of the nadir point, respectively, and θ and These are the observation elevation angle and observation azimuth angle in the antenna coordinate system, respectively; the location of the ground observation target is related to the longitude, latitude and longitude of the nadir point and the antenna observation geometry.

[0016] The relative motion rate between ground observation targets and radar caused by the movement of the satellite platform for:

[0017]

[0018] Where dot() represents the vector dot product operation; The normalized value of the vector pointing from the satellite to the ground observation target is expressed as:

[0019]

[0020] The Doppler frequency shift of the ground observation target is:

[0021]

[0022] Where λ is the wavelength of the observed electromagnetic wave; ignoring the sub-satellite longitude γ, the above... Rewritten as:

[0023]

[0024] The above formula represents the three-dimensional distribution of the Doppler frequency offset as a function of the latitude, azimuth, and pitch of the satellite platform's nadir point.

[0025] As one improvement to the above technical solution, the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer is obtained by utilizing the relationship between the echo frequency and the Doppler frequency shift based on the obtained Doppler frequency offset. This leads to the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite's nadir point. The specific process is as follows:

[0026] Based on the obtained Doppler frequency shift, the echo frequency of the spaceborne sector-beam conical scanning microwave scatterometer is calculated using the relationship between the echo frequency and the Doppler frequency shift.

[0027]

[0028] in, f is the Doppler frequency shift. d0 R0 is the pre-compensation value for the center frequency of the transmitted signal, R0 is the full deslant reference slant range, R is the slant range of the observation beam, a is the frequency modulation slope of the transmitted linear frequency modulated signal, and c is the speed of light.

[0029] By utilizing the relationship between the echo frequency and the Doppler frequency offset of the aforementioned onboard fan-beam conical scanning microwave scatterometer, the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite station's nadir point is obtained.

[0030] As one improvement to the above technical solution, the method involves obtaining a three-dimensional lookup table for slice segmentation based on the three-dimensional distribution of the echo frequency of the satellite's nadir point along with the latitude, azimuth, and elevation directions, using equally spaced ground slices as targets, and obtaining the position of the equally spaced ground slices at the echo frequency corresponding to the pulse sampling point; the specific process is as follows:

[0031] Based on the current latitude of the satellite platform's nadir point and the observation azimuth, the latitude and longitude positions of the current observation footprints on the Earth's ellipsoid surface and the range of the observation footprints on the Earth's ellipsoid surface are obtained.

[0032] According to the pre-set number of slices, based on the latitude and longitude positions of the current Earth ellipsoid observation footprints and the range of Earth ellipsoid observation footprints, the range of Earth ellipsoid observation footprints is divided into equal intervals to determine the latitude and longitude positions of each slice after the equal interval division of Earth ellipsoid observation footprints.

[0033] Based on the determined latitude and longitude positions of each slice, the echo frequency of the beam slice of the spaceborne fan-beam scanning microwave scatterometer is calculated.

[0034]

[0035] in, f is the Doppler frequency offset of the i-th slice; d0,i R(ζ,ξ) is the pre-compensation value for the center frequency of the transmitted signal of the i-th slice; R(ζ,ξ) is the slant range of the scatterometer observation of the i-th slice; ζ is the longitude of the center of the i-th slice; ξ is the latitude of the center of the i-th slice; N s ψ represents the number of slices; ψ represents the latitude of the satellite's nadir point. θ is the observation azimuth angle; θ is the observation elevation angle; R0 is the full deslope reference slant range; a is the frequency modulation slope of the transmitted linear frequency modulated signal; c is the speed of light;

[0036] The echo frequency of the beam slice obtained from the spaceborne fan-beam scanning microwave scatterometer was calculated. The corresponding positions of the echo pulse sampling points on the corresponding echo frequency axis and the number of accumulation points for each slice are determined, thereby obtaining a three-dimensional lookup table for scatterometer slice segmentation for different satellite platforms in terms of latitude intervals, azimuth intervals, and elevation intervals.

[0037] As an improvement to the above technical solution, the three-dimensional segmentation lookup table is further optimized by using equally spaced ground slices as the optimization target to obtain a two-dimensional lookup table for the slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer; the specific process is as follows:

[0038] Using the specified azimuth interval as a reference, obtain the number of start points, end points, and accumulated points of each slice corresponding to the latitude interval of all sub-satellite points in the three-dimensional lookup table for all sub-satellite point segmentation.

[0039] Using the specified azimuth interval k as a reference, assume X i y is the slice number. k,j,i Accumulate the number of sampling points for the pulse slice in the three-dimensional lookup table; Accumulate the starting point for pulse sampling points;

[0040] Where i = 1, 2, ... N s j = 1, 2, ... N l k = 1, 2, ... N a N s N represents the number of accumulated points in each slice of the elevation slice corresponding to all nadir latitude intervals under the specified azimuth interval k. l N represents the number of latitude intervals. a This refers to the number of directional intervals;

[0041] In the three-dimensional lookup table, the cumulative number of sampling points y of the pulse slice is obtained through polynomial fitting.k,j,i With slice number X i The following linear relationship exists:

[0042] y k,j,i =y k,j,0 +k k,j,i X i (6)

[0043] Where, k k,j,i Accumulated slope for slice pulses; y k,j,0 Accumulate the number of sampling points for the first slice of the 3D lookup table;

[0044] For the azimuth interval k, the accumulation starting point after dimensionality reduction processing of the three-dimensional lookup table. for:

[0045]

[0046] End point of accumulation after dimensionality reduction for:

[0047]

[0048] Calculate the slope K of the change in the number of accumulated points in the elevation slice segmentation corresponding to all latitude intervals of the nadir points within the specified azimuth interval. k,i That is, the slope of the pulse accumulation in the slice after dimensionality reduction:

[0049]

[0050] According to K k,i The dimensionality reduction of the three-dimensional lookup table based on the azimuth angle interval k is used to obtain the dimensionality-reduced slice segmentation lookup table, which is then used as the two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer.

[0051] Y k,i =Y k,0 +K k,i X i (10)

[0052] Among them, Y k,0 Accumulate the number of sampling points for the first slice of the dimensionality-reduced two-dimensional lookup table;

[0053] Y k,0 =min(y k,j,0 (11).

[0054] The present invention also provides a two-dimensional lookup table acquisition device for slice segmentation of a spaceborne microwave scatterometer, the device comprising:

[0055] The offset acquisition module is used to obtain the three-dimensional distribution of the Doppler frequency offset with the latitude, azimuth, and pitch of the satellite platform's nadir point, based on the conical scanning observation geometry of the onboard fan-beam microwave scatterer and the relative motion between the satellite platform and the Earth; and to obtain the Doppler frequency offset using the obtained three-dimensional distribution based on the current latitude, azimuth, and pitch of the satellite station's nadir point.

[0056] The three-dimensional distribution acquisition module is used to obtain the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer based on the Doppler frequency offset and the relationship between the echo frequency and the Doppler frequency offset. This allows for the acquisition of the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite station's nadir point.

[0057] The three-dimensional lookup table acquisition module is used to obtain the position of equally spaced ground slices at the echo frequencies corresponding to the pulse sampling points, based on the three-dimensional distribution of the echo frequencies of the spaceborne fan-beam scanning microwave scatterometer with latitude, azimuth, and elevation of the satellite station's nadir point, and using equally spaced ground slices as targets, thus generating a three-dimensional lookup table for slice segmentation; and

[0058] The dimensionality reduction module is used to further optimize the three-dimensional segmentation lookup table by taking equally spaced ground slices as the optimization target, and obtain a two-dimensional lookup table for the segmentation of the spaceborne fan-beam conical scanning microwave scatterometer slices.

[0059] The advantages of this invention compared to the prior art are:

[0060] 1. This invention addresses the issue of fan-beam conical scanning scatterometers. Under the condition that the echo frequency of the fan-beam conical scanning scatterometer is distributed in three dimensions with respect to the latitude, azimuth, and elevation of the nadir point, it aims to achieve approximately equal intervals in ground footprint slices and presents the slice accumulation process of pulse sampling points in the form of a lookup table. This solves the problem that existing equal-frequency division methods are not applicable to ground footprint slice segmentation in fan-beam conical scanning scatterometers, while also considering the real-time performance and robustness of onboard implementation.

[0061] 2. This invention first establishes a three-dimensional lookup table method for segmenting fan-beam conical scanning scatterometer slices based on signal characteristics. On this basis, the three-dimensional lookup table is processed using echo frequency minimum envelope processing and slope transformation processing to achieve dimensionality reduction optimization of the fan-beam conical scanning scatterometer slice segmentation lookup table. The process and algorithm for obtaining the fan-beam conical scanning scatterometer slice segmentation lookup table are provided. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the observation geometry of the existing CSCAT scatterometer;

[0063] Figure 2 This is the Doppler frequency distribution diagram of CSCAT;

[0064] Figure 3 This is a schematic diagram of the CSCAT slice segmentation two-dimensional lookup table acquisition method;

[0065] Figure 4 It is a CSCAT slice segmentation two-dimensional lookup table;

[0066] Figure 5 This is a distribution map of the starting points of the distance gate recombination in the CSCAT slice segmentation two-dimensional lookup table.

[0067] Figure 6 It is the ground slice scale after CSCAT application slice segmentation two-dimensional lookup table. Detailed Implementation

[0068] The present invention will now be further described in conjunction with the accompanying drawings and examples.

[0069] like Figure 1 and 3 As shown, this invention provides a method for obtaining a two-dimensional lookup table for slice segmentation of a fan-beam conical scanning microwave scatterometer. The method includes:

[0070] Based on the conical scanning observation geometry of the spaceborne fan-beam microwave scatterometer, and combined with the relative motion between the satellite platform and the Earth, the three-dimensional distribution of the Doppler frequency shift with the latitude, azimuth, and pitch of the satellite platform's nadir point is obtained; based on the current latitude, azimuth, and pitch of the satellite station's nadir point, the obtained three-dimensional distribution is used to obtain the Doppler frequency shift.

[0071] Based on the Doppler frequency offset, the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer is obtained by utilizing the relationship between the echo frequency and the Doppler frequency offset. This leads to the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite's nadir point. Since the Doppler frequency offset has a three-dimensional distribution with respect to the latitude, azimuth, and elevation of the satellite's nadir point, the echo frequency of the fan-beam conical scanning microwave scatterometer also has a three-dimensional distribution with respect to the latitude, azimuth, and elevation of the nadir point.

[0072] Based on the three-dimensional distribution of echo frequencies of the spaceborne fan-beam scanning microwave scatterometer with the latitude, azimuth, and elevation of the satellite station's nadir point, and using equally spaced ground slices as targets, the positions of the equally spaced ground slices at the echo frequencies corresponding to the pulse sampling points are obtained, resulting in a three-dimensional lookup table for slice segmentation. The slice segmentation process of the spaceborne fan-beam conical scanning microwave scatterometer involves accumulating observation pulse sampling points at different nadir points with different latitudes, azimuths, and elevations according to the number of accumulated sampling points given in the lookup table, so that the observation slices after the sampling points are accumulated are equally spaced in the observation area on the ground.

[0073] Then, using equally spaced ground slices as the optimization target, the three-dimensional segmentation lookup table is optimized by dimensionality reduction to obtain a two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer.

[0074] Specifically, based on the specified azimuth interval, the number of pitch slice segmentation start points, the number of accumulation end points, and the number of accumulation points for each slice are obtained for all sub-satellite latitude intervals in the three-dimensional lookup table.

[0075] The minimum and maximum values ​​of the starting and ending points of the elevation slice accumulation within the specified azimuth interval are obtained. These values ​​are then used as the accumulation range after dimensionality reduction to ensure that the echo frequencies corresponding to observations within all latitude intervals of nadir points within the specified azimuth interval are included in the corresponding frequency range after dimensionality reduction. This process is called echo frequency minimum envelope processing. The number of accumulation points in each slice of the elevation slice corresponding to all latitude intervals of nadir points within the specified azimuth interval is used to calculate the slope of the change in the number of accumulation points in the elevation slice. Through data fitting, the correspondence between the echo pulse sampling point accumulation range and the slope of the change in the number of accumulation points in the elevation slice is obtained. Based on this correspondence, the slope of the change in the number of accumulation points in the sample accumulation range after dimensionality reduction is calculated. This process is called slope transformation processing.

[0076] Using the specified azimuth interval k as a reference, assume X i y is the slice number. k,j,i Accumulate the number of sampling points for the pulse slice in the three-dimensional lookup table; Accumulate the starting point for pulse sampling points;

[0077] Where i = 1, 2, ... N s j = 1, 2, ... N l k = 1, 2, ... N a N s N represents the number of accumulated points in each slice of the elevation slice corresponding to all nadir latitude intervals under the specified azimuth interval k. l N represents the number of latitude intervals.a This refers to the number of directional intervals;

[0078] In the three-dimensional lookup table, the cumulative number of sampling points y of the pulse slice is obtained through polynomial fitting. k,j,i With slice number X i The following linear relationship exists:

[0079] y k,j,i =y k,j,0 +k k,j,i X i (6)

[0080] Where, k k,j,i Accumulated slope for slice pulses; y k,j,0 Accumulate the number of sampling points for the first slice of the 3D lookup table;

[0081] For the azimuth interval k, the accumulation starting point after dimensionality reduction processing of the three-dimensional lookup table. for:

[0082]

[0083] End point of accumulation after dimensionality reduction for:

[0084]

[0085] Calculate the slope K of the change in the number of accumulated points in the elevation slice segmentation corresponding to all latitude intervals of the nadir points within the specified azimuth interval. k,i That is, the slope of the pulse accumulation in the slice after dimensionality reduction:

[0086]

[0087] According to K k,i The dimensionality reduction of the three-dimensional lookup table based on the azimuth angle interval k is used to obtain the dimensionality-reduced slice segmentation lookup table, which is then used as the two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer.

[0088] Y k,i =Y k,0 +K k,i X i (10)

[0089] Among them, Y k,0 Accumulate the number of sampling points for the first slice of the dimensionality-reduced two-dimensional lookup table;

[0090] Y k,0 =min(y k,j,0 (11)

[0091] Based on the obtained two-dimensional lookup table of slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer, the observation sample points corresponding to the echo frequencies of all observations in the latitude interval of the nadir point within the azimuth interval are all included within the sample point range of the dimension-reduced lookup table; thus, two-dimensional lookup tables for slice segmentation of different azimuth and elevation intervals are obtained.

[0092] After the echo frequency minimum envelope processing shown in equations (7) and (8) and the slope transformation processing shown in equation (9), the dimensionality reduction processing of the three-dimensional lookup table based on the azimuth interval is completed. After the dimensionality reduction processing, the observation samples corresponding to the echo frequencies of all observations in the latitude intervals of the nadir points within the azimuth interval are included in the sample range of the dimensionality-reduced lookup table. At this time, the latitude dimension in the three-dimensional lookup table is eliminated, and the three-dimensional lookup table with slicing of latitude intervals, azimuth intervals and elevation intervals of different satellite platforms is transformed into a two-dimensional lookup table with slicing of different azimuth intervals and elevation intervals.

[0093] Based on the slice-segmented three-dimensional lookup table, the minimum envelope of the echo frequency is used as the accumulation range of the pulse sampling point distance gate in the two-dimensional lookup table. A slope transform algorithm is employed to achieve dimensionality reduction optimization of the slice-segmented lookup table in two dimensions.

[0094] A two-dimensional lookup table method in azimuth and elevation directions is used to segment the scatterometer's ground observation footprint, ensuring that the slice sizes are approximately equal. For the current observation pulse, the starting point for accumulation of sampling points in the azimuth and elevation directions and the number of accumulation points in each slice are obtained from the slice segmentation lookup table based on its observation azimuth angle. Then, the power of the current pulse sampling points is accumulated based on the accumulation starting point and the number of accumulation points in each slice to obtain the power value corresponding to each slice. The slice power values ​​obtained in this way correspond to the echo power values ​​of approximately equally spaced observation areas on the Earth's surface.

[0095] This invention proposes a two-dimensional lookup table method for segmenting slices of a spaceborne fan-beam conical scanning microwave scatterometer. To meet the requirements of real-time processing, a lookup table is used to complete the segmentation of pulse footprints, and the three-dimensional lookup table for slice segmentation is optimized by dimensionality reduction to obtain a two-dimensional lookup table for segmenting slices of a spaceborne fan-beam conical scanning microwave scatterometer.

[0096] The present invention also provides a two-dimensional lookup table acquisition device for slice segmentation of a spaceborne microwave scatterometer, the device comprising:

[0097] The offset acquisition module is used to obtain the three-dimensional distribution of the Doppler frequency offset with the latitude, azimuth, and pitch of the satellite platform's nadir point, based on the conical scanning observation geometry of the onboard fan-beam microwave scatterer and the relative motion between the satellite platform and the Earth; and to obtain the Doppler frequency offset using the obtained three-dimensional distribution based on the current latitude, azimuth, and pitch of the satellite station's nadir point.

[0098] The three-dimensional distribution acquisition module is used to obtain the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer based on the Doppler frequency offset and the relationship between the echo frequency and the Doppler frequency offset. This allows for the acquisition of the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite station's nadir point.

[0099] The three-dimensional lookup table acquisition module is used to obtain the position of equally spaced ground slices at the echo frequencies corresponding to the pulse sampling points, based on the three-dimensional distribution of the echo frequencies of the spaceborne fan-beam scanning microwave scatterometer with latitude, azimuth, and elevation of the satellite station's nadir point, and using equally spaced ground slices as targets, thus generating a three-dimensional lookup table for slice segmentation; and

[0100] The dimensionality reduction module is used to further optimize the three-dimensional segmentation lookup table by taking equally spaced ground slices as the optimization target, and obtain a two-dimensional lookup table for the segmentation of the spaceborne fan-beam conical scanning microwave scatterometer slices.

[0101] Example 1.

[0102] This invention, using the China-France Oceanographic Satellite (CFOSAT) as a background and slice-segmented range-gate reconstruction as a baseline, provides a detailed analysis of the microwave scatterometers of the CFOSAT (such as...). Figure 1 (as shown) (CSCAT) Doppler frequency distribution Figure 2 Based on the ground slice approximation of the same scale (as shown in the figure) and echo frequency distribution, a three-dimensional lookup table for slice segmentation related to latitude, azimuth, and pitch was obtained. On this basis, dimensionality reduction optimization was performed to obtain a two-dimensional lookup table for slice segmentation. Figure 3 This is a flowchart of the method of the present invention.

[0103] A three-dimensional lookup table algorithm for slice segmentation is established using ground slices as equally spaced observation slices as the basic constraint. Furthermore, the dimensionality reduction optimization of the three-dimensional lookup table for slice segmentation is achieved using the echo frequency envelope minimization and slope transformation algorithms, thus obtaining a method for acquiring a two-dimensional lookup table for slice segmentation.

[0104] The CSCAT azimuth uses 64 equally spaced angular intervals, with an angular interval of 5.625°.

[0105] After signal extraction, the sampling rate is reduced to 1.5MHz; distance information will be extracted from the fully descrambled signal using 4096-FFT, and after slicing, it will be reassembled into 40 slices for downlink.

[0106] To accurately extract distance information and appropriately accumulate 4096 points in the pulse based on approximately equal-sized slices on the ground, the residual Doppler frequency shift should be carefully compensated. Based on the relationship between echo frequency and elevation angle, the corresponding frequencies for equal-sized ground slices are obtained through spline interpolation, and a three-dimensional slice segmentation lookup table is derived based on azimuth, latitude, and elevation directions. However, if the residual Doppler frequency is fully compensated, the on-board processing complexity will increase significantly. Dimensionality reduction optimization eliminates the dimensionality of the three-dimensional slice segmentation lookup table. In the lookup table dimensionality reduction optimization, for specific azimuth angle elements, the accumulation point boundaries of the one-dimensional lookup table are determined to ensure that points of different latitudes in the three-dimensional lookup table are included, and the accumulation slope of the one-dimensional lookup table is adjusted accordingly based on the accumulation slopes of all latitudes. The CSCAT two-dimensional slice segmentation lookup table obtained by this invention is as follows: Figure 4 and Figure 5 As shown. For the actual observed pulse, by Figure 5 The starting point for slice segmentation and accumulation is determined based on the azimuth interval of the slice at the pulse sampling point. Then, starting from the accumulation starting point, each sequence slice is accumulated according to the number of accumulation points given by the lookup table, based on its azimuth interval. After accumulation at the CSCAT pulse sampling points, 40 slices are obtained, which are approximately equally spaced within the ground observation area. The dimensionality reduction optimization using the three-dimensional lookup table significantly improves the complexity of on-board processing; on the other hand, the ground slices are approximately the same size, such as... Figure 6 As shown, for certain azimuth angles and slice indices, the average slice width is approximately 10.2 km, with a maximum of 10.4 km. Considering the low signal-to-noise ratio and potential echo energy leakage, some edge slices should be discarded to extract backscattering coefficients. For CSCAT, variable slice resolution can be obtained through on-orbit annotation.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for obtaining a two-dimensional lookup table for slice segmentation of a spaceborne microwave scatterometer, the method comprising: Based on the conical scanning observation geometry of the spaceborne fan-beam conical scanning microwave scatterometer, and combined with the relative motion between the satellite platform and the Earth, the three-dimensional distribution of the Doppler frequency shift with the latitude, azimuth, and pitch of the satellite platform's nadir point is obtained; based on the current latitude, azimuth, and pitch of the satellite station's nadir point, the obtained three-dimensional distribution is used to obtain the Doppler frequency shift. Based on the Doppler frequency offset, the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer is obtained by using the relationship between the echo frequency and the Doppler frequency offset. Then, the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with the latitude, azimuth and elevation of the satellite station's nadir point is obtained. Based on the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with the latitude, azimuth and elevation of the satellite station's nadir point, and taking equally spaced ground slices as targets, the position of the equally spaced ground slices at the echo frequency corresponding to the pulse sampling point is obtained, and a three-dimensional lookup table for slice segmentation is obtained. Then, using equally spaced ground slices as the optimization target, the three-dimensional segmentation lookup table is optimized for dimensionality reduction to obtain a two-dimensional lookup table for the slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer. The specific process is as follows: Using the specified azimuth interval as a reference, obtain the number of start points, end points, and accumulated points of each slice corresponding to the latitude interval of all sub-satellite points in the three-dimensional lookup table for all sub-satellite point segmentation. With a specified azimuth interval k As a benchmark, assuming The slice number. Accumulate the number of sampling points for the pulse slice in the three-dimensional lookup table; Accumulate the starting point for pulse sampling points; in, , , , For the specified azimuth interval k The accumulated number of points in each slice corresponding to the elevation slice of all sub-satellite latitude intervals. Number of latitude intervals This refers to the number of directional intervals; In the three-dimensional lookup table, the cumulative number of sampling points of the pulse slice is obtained through polynomial fitting. With slice number The following linear relationship exists: in, Accumulate slope for slice pulses; Accumulate the number of sampling points for the first slice of the 3D lookup table; For the azimuth interval k The starting point for accumulation after dimensionality reduction of the 3D lookup table for: End point of accumulation after dimensionality reduction for: Calculate the slope of the change in the number of accumulated points in the elevation slice segment corresponding to all latitude intervals of the nadir points within the specified azimuth interval. That is, the slope of the pulse accumulation in the slice after dimensionality reduction: according to , in azimuth interval k The dimensionality reduction of the three-dimensional lookup table based on the slice segmentation is used to obtain the dimensionality-reduced slice segmentation lookup table, which is then used as the two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer. in, Accumulate the number of sampling points for the first slice of the dimensionality-reduced two-dimensional lookup table; 。 2. The method for obtaining a two-dimensional lookup table for segmentation of a spaceborne microwave scatterometer according to claim 1, characterized in that, The method involves obtaining the three-dimensional distribution of Doppler frequency shift with latitude, azimuth, and pitch of the satellite platform's nadir point based on the conical scanning observation geometry of the spaceborne fan-beam conical scanning microwave scatterometer and the relative motion between the satellite platform and the Earth. The specific process is as follows: Assumption and These are the position and velocity vectors of the satellite platform in the Earth-fixed coordinate system. This is the position vector of the ground observation target in the Earth-fixed coordinate system; in, and These are the longitude and latitude of the nadir point, respectively. and These are the observation elevation angle and observation azimuth angle in the antenna coordinate system, respectively; the location of the ground observation target is related to the longitude, latitude and longitude of the nadir point and the antenna observation geometry. The relative motion rate between ground observation targets and radar caused by the movement of the satellite platform for: in, This represents the vector dot product operation; The normalized value of the vector pointing from the satellite to the ground observation target is expressed as: The Doppler frequency shift of the ground observation target is: in, To observe the wavelength of electromagnetic waves; nadir longitude is ignored. The above Rewritten as: The above formula represents the three-dimensional distribution of the Doppler frequency offset as a function of the latitude, azimuth, and pitch of the satellite platform's nadir point.

3. The method for obtaining a two-dimensional lookup table for segmentation of a spaceborne microwave scatterometer according to claim 1, characterized in that, Based on the Doppler frequency offset, the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer is obtained by utilizing the relationship between the echo frequency and the Doppler frequency offset. This leads to the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite's nadir point. The specific process is as follows: Based on the obtained Doppler frequency shift, the echo frequency of the spaceborne sector-beam conical scanning microwave scatterometer is calculated using the relationship between the echo frequency and the Doppler frequency shift. : in, This is the Doppler frequency shift. This is the pre-compensation value for the center frequency of the transmitted signal. For full slope removal, the reference slope distance is... To observe the beam slant range, To transmit a linear frequency modulated signal, the frequency modulation slope, At the speed of light, The latitude of the satellite's nadir point. To observe the pitch angle, To observe the azimuth angle; By utilizing the relationship between the echo frequency and the Doppler frequency offset of the aforementioned spaceborne fan-beam conical scanning microwave scatterometer, the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite station's nadir point is obtained.

4. The method for obtaining a two-dimensional lookup table for segmentation of a spaceborne microwave scatterometer according to claim 1, characterized in that, The method is to obtain the position of the equally spaced ground slices at the echo frequency corresponding to the pulse sampling point based on the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with the latitude, azimuth and elevation of the satellite station's nadir point, and to obtain a three-dimensional lookup table for slice segmentation by taking equally spaced ground slices as targets. The specific process is as follows: Based on the current latitude of the satellite platform's nadir point and the observation azimuth, the latitude and longitude positions of the current observation footprints on the Earth's ellipsoid surface and the range of the observation footprints on the Earth's ellipsoid surface are obtained. According to the pre-set number of slices, based on the latitude and longitude positions of the current Earth ellipsoid observation footprints and the range of Earth ellipsoid observation footprints, the range of Earth ellipsoid observation footprints is divided into equal intervals to determine the latitude and longitude positions of each slice after the equal interval division of Earth ellipsoid observation footprints. Based on the determined latitude and longitude positions of each slice, the echo frequency of the beam slice of the spaceborne fan-beam conical scanning microwave scatterometer is calculated. : in, The Doppler frequency offset of the i-th slice; This is the pre-compensation value for the center frequency of the transmitted signal in the i-th slice; The slant range observed by the scatterometer for the i-th slice; Let the longitude of the center of the i-th slice be _i_. Let be the latitude of the center of the i-th slice; The number of slices; The latitude of the satellite's nadir point; To observe the azimuth angle; To observe the pitch angle; The reference slope distance for full slope removal; The frequency modulation slope for transmitting a linear frequency modulated signal; The speed of light; The echo frequency of the beam slice obtained from the calculated spaceborne fan-beam conical scanning microwave scatterometer The corresponding positions of the echo pulse sampling points on the corresponding echo frequency axis and the number of accumulation points for each slice are determined, thereby obtaining a three-dimensional lookup table for scatterometer slice segmentation for different satellite platforms in terms of latitude intervals, azimuth intervals, and elevation intervals.

5. A device for obtaining a two-dimensional lookup table for slice segmentation of a spaceborne microwave scatterometer, characterized in that, The device includes: The offset acquisition module is used to obtain the three-dimensional distribution of the Doppler frequency offset with the latitude, azimuth, and pitch of the satellite platform's nadir point, based on the conical scanning observation geometry of the spaceborne fan-beam conical scanning microwave scatterometer and the relative motion between the satellite platform and the Earth; and to obtain the Doppler frequency offset using the obtained three-dimensional distribution based on the current latitude, azimuth, and pitch of the satellite station's nadir point. The three-dimensional distribution acquisition module is used to obtain the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer based on the Doppler frequency offset and the relationship between the echo frequency and the Doppler frequency offset. This allows for the acquisition of the three-dimensional distribution of the echo frequency of the spaceborne fan-beam conical scanning microwave scatterometer with respect to the latitude, azimuth, and elevation of the satellite station's nadir point. The three-dimensional lookup table acquisition module is used to obtain the position of equally spaced ground slices at the echo frequencies corresponding to the pulse sampling points, based on the three-dimensional distribution of the echo frequencies of the spaceborne fan-beam conical scanning microwave scatterometer with latitude, azimuth, and elevation of the satellite station's nadir point, and using equally spaced ground slices as targets, thus generating a three-dimensional lookup table for slice segmentation; and The dimensionality reduction module is used to further optimize the three-dimensional segmentation lookup table by using equally spaced ground slices as the optimization target, thereby obtaining a two-dimensional lookup table for the slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer. The specific process is as follows: Using the specified azimuth interval as a reference, obtain the number of start points, end points, and accumulated points of each slice corresponding to the latitude interval of all sub-satellite points in the three-dimensional lookup table for all sub-satellite point segmentation. With a specified azimuth interval k As a benchmark, assuming The slice number. Accumulate the number of sampling points for the pulse slice in the three-dimensional lookup table; Accumulate the starting point for pulse sampling points; in, , , , For the specified azimuth interval k The accumulated number of points in each slice corresponding to the elevation slice of all sub-satellite latitude intervals. Number of latitude intervals This refers to the number of directional intervals; In the three-dimensional lookup table, the cumulative number of sampling points of the pulse slice is obtained through polynomial fitting. With slice number The following linear relationship exists: in, Accumulate slope for slice pulses; Accumulate the number of sampling points for the first slice of the 3D lookup table; For the azimuth interval k The starting point for accumulation after dimensionality reduction of the 3D lookup table for: End point of accumulation after dimensionality reduction for: Calculate the slope of the change in the number of accumulated points in the elevation slice segment corresponding to all latitude intervals of the nadir points within the specified azimuth interval. That is, the slope of the pulse accumulation in the slice after dimensionality reduction: according to , in azimuth interval k The dimensionality reduction of the three-dimensional lookup table based on the slice segmentation is used to obtain the dimensionality-reduced slice segmentation lookup table, which is then used as the two-dimensional lookup table for slice segmentation of the spaceborne fan-beam conical scanning microwave scatterometer. in, Accumulate the number of sampling points for the first slice of the dimensionality-reduced two-dimensional lookup table; 。

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