CN116626629A - Fuzzy comprehensive performance evaluation method for satellite-borne strabismus SAR system - Google Patents
Fuzzy comprehensive performance evaluation method for satellite-borne strabismus SAR system Download PDFInfo
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Abstract
The invention provides a fuzzy comprehensive performance evaluation method of a satellite-borne squint SAR system, which establishes a precise geometrical model of the satellite-borne SAR by combining specific satellite-to-ground geometrical information, precisely divides the fuzzy of the SAR system by analyzing Doppler frequency and squint distance, precisely calculates different fuzzy energy of the satellite-borne SAR system under any squint angle on the basis of fully considering precise orbit model, antenna attitude information and antenna pattern information, and finally obtains fuzzy performance parameters of the satellite-borne SAR system. The invention provides a generalized fuzzy performance calculation method for any squint angle spaceborne SAR system.
Description
Technical Field
The invention belongs to the field of SAR systems and SAR image quality evaluation, and particularly relates to a fuzzy comprehensive performance evaluation method of a satellite-borne strabismus SAR system.
Background
The synthetic aperture radar (Synthetic Aperture Radar, SAR) satellite is one of the most important information acquisition platforms in the remote sensing field by virtue of the characteristics of full time, all weather, multiple polarization, strong penetrability, wide coverage area and the like, and is widely applied to the fields of agricultural monitoring, topographic mapping, environmental monitoring, disaster relief and the like.
When designing a space-borne SAR system, because the space-borne SAR is not an ideal sensor, the imaging performance is limited by the system characteristics and inherent constraints, and the main performance indexes of the traditional single-channel space-borne SAR system are as follows: geometric resolution, mapping bandwidth, system sensitivity, and blur performance. The SAR system blurring performance has a large influence on SAR image quality, and distance blurring and azimuth blurring are two important indexes for representing SAR system imaging quality.
For conventional front-side or small squint SAR systems, the SAR sensor employs a corresponding two-dimensional pattern of antennas, as shown in FIG. 1, whose distance and azimuth directions are mutually orthogonal. The system ambiguity performance can be generally estimated by a range ambiguity ratio and an azimuth ambiguity ratio index.
(1) Distance ambiguity performance evaluation method
Since the SAR system is not ideally directed to a beam pattern, its beam illumination practical range is greater than the mapping bandwidth. When the useful echoes in the range direction return to the SAR antenna, part of the extra echo energy outside the mapping bandwidth, which is called range-obscuring energy, also enters the radar receiving window at the same time, these extra echoes mix with the useful echoes and affect the SAR imaging quality after the imaging process. Since the SAR system signal transmission mode takes the form of continuous pulse transmission, it is known that for the currently received useful echo signal, its range-ambiguous energy comes from the mapped out-of-band echo signal of several transmitted pulses before or after, as shown in fig. 2 and 3.
Typically, for distance blur, the evaluation is performed using a distance blur ratio RASR (Range Ambiguity to Signal Ratio):
，
in the formula ,and->Respectively represent +.>The lower view angle corresponding to the step distance blur corresponds to the lower view angle corresponding to the main signal; />Indicate->The incident angle corresponding to the position of the step distance blur is +.>An incident angle corresponding to the useful signal of the main lobe region; />Backscattering coefficient representing ground object of corresponding scene, incidence angle with scene object type, signal wavelength and beam illumination +.>Related to; />Representing the corresponding slant distance of the scene ground; />And->Respectively indicating the angles of the system receiving antenna and the system transmitting antenna as +.>The gain factor of the time is mainly related to the effective area of the antenna adopted by the system, the distance direction normalization pattern of the antenna and the wavelength of the signal adopted by the system. For a single channel SAR system, it can be considered +.>And->Gain strength is the same. The smaller the distance blur ratio RASR of the system, the less the blur energy in the useful echo it corresponds to, and the better the distance blur performance of the imaged image.
(2) Direction ambiguity performance evaluation method
The SAR system irradiates targets in azimuth through radar beams, and as the SAR platform moves, the SAR system corresponds to different azimuth time for the same targetIs->Forming different Doppler frequencies in azimuth echo signals>And constitutes an azimuth signal. Effective Doppler bandwidth of the Doppler frequency +.>Related to the beamwidth of the azimuth antenna.
However, like the range-to-antenna pattern, the SAR system is also not ideal in the azimuth antenna pattern, and the actual beamwidth of the azimuth antenna is wider than the ideal beamwidth (3 dB width of the main lobe of the antenna pattern). At this time, the echo energy outside the 3dB main lobe width corresponding to the azimuth will enter the receiver as well, and the corresponding Doppler frequency will be higher than the ideal effective Doppler bandwidth. Because the azimuth sampling rate of the SAR system is PRF, according to the sampling theorem, the azimuth signal can be subjected to spectrum aliasing, and the azimuth signal is positioned at +.>Out-of-band energy will also mix into the effective band +.>In this case, an azimuth ambiguity is formed as shown in fig. 4.
Generally, for the azimuth ambiguity, the azimuth ambiguity ratio AASR (Azimuth Ambiguity to Signal Ratio) is used for evaluation:
，
wherein ,the antenna pattern weight of the azimuth direction is squared to represent the antenna pattern power of the SAR system receiving and transmitting double-pass; />The doppler spectrum amplitude is weighted.
In the design flow of the space-borne SAR system, the fuzzy performance of the SAR system is generally evaluated by adopting a distance fuzzy and azimuth fuzzy two-dimensional fuzzy ratio evaluation method, and the main problems are as follows:
the SAR image is a two-dimensional image, the antenna corresponding pattern is a two-dimensional pattern, the conventional calculation mode of the distance blur ratio RASR and the azimuth blur ratio AASR only calculates the ratio of the blur energy in the two-dimensional directions of the independent distance direction and the azimuth direction to the SAR target energy, and the gain influence of the antenna pattern in the two-dimensional directions of the distance direction and the azimuth direction is ignored.
For the front side view and small squint SAR system, the distance direction and the azimuth direction are orthogonal to each other, and the distance direction and the azimuth direction exactly correspond to the two-dimensional strong gain side lobe positions of the antenna pattern, and the rest of the blurring in the two-dimensional blurring ratio calculation corresponds to the weak gain side lobe positions of the antenna pattern, so that the blurring energy is small and can be ignored. However, for the SAR system with a larger squint angle, the squint angle increases to cause the antenna to deviate in pointing direction, and further, the antenna azimuth direction and the distance direction diagram are no longer matched and correspond to the azimuth direction and the distance direction of the mapping scene, so that the blur is no longer independently distributed in the two-dimensional direction of the antenna, and a new blur performance evaluation method needs to be re-analyzed and set for the blur distribution condition under the squint condition.
Disclosure of Invention
Aiming at the technical problems, the invention provides a fuzzy comprehensive performance evaluation method of a satellite-borne squint SAR system, which starts from a complex satellite-ground geometric relationship of the satellite-borne squint SAR system, evaluates satellite-ground projection relationship of satellite-borne SAR antenna beams by a coordinate system transformation method, evaluates beam direction target signals and corresponding fuzzy signals of the squint SAR system by combining SAR antenna pattern gain conditions, and finally realizes fuzzy energy statistics and fuzzy performance evaluation in strabismus SAR system design.
According to the invention, a precise geometric model of the spaceborne SAR is established by combining specific spaceborne geometric information, the fuzzy of the SAR system is precisely divided by analyzing Doppler frequency and slant range, different fuzzy energy of the spaceborne SAR system under any slant angle is precisely calculated on the basis of fully considering the precise orbit model, antenna attitude information and antenna pattern information, and finally the fuzzy performance parameters of the spaceborne SAR system are obtained. The invention provides a generalized fuzzy performance calculation method for any squint angle spaceborne SAR system.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a fuzzy comprehensive performance evaluation method of a satellite-borne strabismus SAR system comprises the following steps:
s1: establishing a satellite-ground geometric relation model of a satellite-borne SAR system under the condition of any squint angle according to SAR satellite platform position information, SAR antenna gesture, satellite platform speed, satellite gesture information and SAR antenna beam two-dimensional scanning angle parameters, and calculating to obtain parameter information of instantaneous Doppler frequency, instantaneous distance and instantaneous incidence angle at any position in an imaging scene;
s2: carrying out fuzzy classification on any position in an imaging scene according to the instantaneous Doppler frequency, the instantaneous distance and the instantaneous incidence angle parameter information of any position in the scene; determining a value range of Doppler frequency and a value range of a diagonal distance of a target scene according to SAR imaging set resolution and breadth information, and determining a Doppler frequency range and a diagonal range corresponding to a target scene area and each fuzzy area;
s3: based on the satellite-ground geometric model and imaging scene oblique distance information and incidence angle information, respectively calculating corresponding target scenes and backscattering coefficients corresponding to different fuzzy scenes; respectively calculating antenna pattern gains corresponding to the target scene and different fuzzy scenes based on the two-dimensional antenna pattern gains;
s4: respectively calculating energy intensities corresponding to a corresponding target scene and different fuzzy scenes based on the antenna pattern gain, the inclined distance range and the backscattering coefficient; and calculating the fuzzy ratio indexes of different fuzzes of any squint angle space-borne SAR system according to the definition of the fuzzy ratio.
Further, the step S1 includes:
s11: grid division is carried out on an imaging scene, scene coordinate information is established, and the instantaneous height of the satellite platform is combined according to scene coordinates in the imaging sceneDetermining the current position star-to-ground instantaneous downview angle +.>；
S12: satellite-to-earth instantaneous viewing angle according to current positionDetermining the current coordinate star-to-earth instantaneous angle of incidence +.>：
，
wherein ,is the earth radius;
s13: satellite-to-earth instantaneous viewing angle according to current positionAnd the current coordinate star-to-earth instantaneous angle of incidence +.>Determining the corresponding skew of the current coordinates/>：
，
S14: determining instantaneous Doppler frequency of instantaneous time coordinate point according to instantaneous time SAR satellite position and satellite platform speed；
，
wherein ,for the instantaneous speed of the satellite relative to the current coordinate point, +.>For the instantaneous skew of the satellite relative to the current coordinate point, vector multiplication +.>Representing the instantaneous relative velocity of the satellite and the coordinate point.
Further, the step S2 includes:
s21: determining the corresponding slant range of the SAR target scene according to the imaging breadth or the angle range of the lower viewing angle required by the SAR systemThe value range-> and />, wherein />For imaging the proximal diagonal of the swath,for imaging breadth far-end slant distance, satisfy:
，
s22: beam center squint angle set according to SAR systemAzimuth resolution->Determining the Doppler center frequency of the target scene>And corresponding Doppler bandwidth->And determining the Doppler frequency corresponding to the target scene>Is defined in the following range:
，
s23: corresponding to the target scene meeting S21 in the imaging sceneDoppler frequency corresponding to the target scene of S22>The coordinate position of the value range of (2) is marked as a target scene;
s24: determining the corresponding slant distance of any fuzzy scene area according to the pulse transmitting frequency PRF set by the SAR systemAnd Doppler frequency->Is defined in the following range:
，
，
wherein ,fuzzy Doppler spectrum aliasing number representing azimuth, < >>Fuzzy distance direction scene aliasing number representing distance direction, +.>Is->Doppler frequency of order bearing ambiguity, +.>Is->The slant distance of the step distance blur;
s25: according to the corresponding slant distance of any blurred scene area in S24And Doppler frequencyTo classify the non-target scene area into a fuzzy area: will->Is marked as azimuth ambiguous area, +.>Is marked as a distance blurred region, willIs marked as a coupled ambiguous region.
Further, the step S3 includes:
s31: inquiring and acquiring scattering model parameters corresponding to the imaged ground object types by combining the imaged ground object typesValues, noted as:
，
in the formula ,calculating model parameter values for the scattering intensity;
s32: corresponding to the satellite-ground instantaneous incident angle according to any coordinate point of the scene in S12Combining scattering model parameters corresponding to different ground objects in different frequency bands in S31>Value, obtain electromagnetic back scattering intensity empirical reference value +.>The unit is dB:
；
wherein exp () represents an exponential function based on a natural constant e;
s33: converting the radar coordinate system to the antenna coordinate system for any coordinate of the scene in S1, and according to the directional parameters corresponding to the coordinatesAnd based on a priori two dimensionsAntenna pattern transmit-receive gain-> and />Obtaining the receiving and transmitting gain intensity of the two-dimensional antenna pattern corresponding to any coordinate of the scene> and />。
Further, the step S4 includes:
s41: receiving and transmitting gain strength combined with two-dimensional antenna pattern and />Corresponding to the target scene in S21, skew +.>Doppler frequency corresponding to the target scene in S22 +.>Calculating the energy intensity of the main signal of the target scene +.>：
，
wherein ,is of oblique distance and is->Is the back scattering intensity;
s42: transmit-receive augmentation combined with two-dimensional antenna patternAccording to the fuzzy classification result in S25, calculating the fuzzy signal energy intensity azimuth fuzzy intensity corresponding to different fuzzy areasDistance blur intensity->Coupling ambiguity intensity->：
，
，
，
wherein ,diagonal distance for distance blur of 0 th order, +.>Doppler frequency for order 0 azimuth ambiguity; />Corresponding incidence angle values for the fuzzy regions;
s43: when SAR system index design is performed, fuzzy strength is usedEnergy intensity of main signal with target sceneIs calculated as the ratio of (2) fuzzy ratio->：
，
Sequentially obtaining corresponding fuzzy performance evaluation index fuzzy ratios according to the above steps: azimuth blur ratio AASR, distance blur ratio RASR, coupling blur ratio CASR, and total blur ratio ASR.
The beneficial effects are that:
according to the invention, a precise geometric model of the spaceborne SAR is established by combining specific spaceborne geometric information, the ambiguity of the SAR system is precisely divided by analyzing Doppler frequency and slant range, and different ambiguity energy of the spaceborne SAR system under any slant angle is precisely calculated on the basis of fully considering the precise orbit model, antenna attitude information and antenna pattern information, so that the ambiguity performance parameters of the arbitrary strabismus spaceborne SAR system can be finally obtained.
Drawings
FIG. 1 is a two-dimensional antenna pattern (elevation view angle 42.5 degrees) of a front side-view SAR system;
fig. 2 is a schematic diagram of a principle of forming distance ambiguity of a satellite-borne SAR platform;
FIG. 3 is a schematic diagram of a satellite-borne SAR platform range ambiguity beam state;
FIG. 4 is a schematic diagram of a principle of forming azimuth ambiguity of a satellite-borne SAR platform;
FIG. 5 is a flow chart of a fuzzy comprehensive performance evaluation method of the satellite-borne squint SAR system;
FIG. 6a and FIG. 6b are the front-side view and 40℃large squint antenna pattern projection results in the embodiment; wherein, fig. 6a is a front side view, and fig. 6b is a projection result of a large squint antenna pattern;
FIG. 7a and FIG. 7b are range-Doppler two-dimensional graphs of the range-ambiguity region for each order of azimuth in an embodiment; wherein, fig. 7a is a front side view, and fig. 7b is a large oblique view, a transverse view and an azimuth view;
FIG. 8a and FIG. 8b are two-dimensional graphs of range-Doppler for range-blur areas of various orders in an embodiment; wherein, fig. 8a is a left side view, and fig. 8b is a large oblique view, longitudinal, distance view;
FIG. 9a and FIG. 9b are range-Doppler two-dimensional graphs of coupling ambiguity regions of various orders in an embodiment; wherein, fig. 9a is a left side view, and fig. 9b is a large oblique view, longitudinal, distance view;
FIG. 10a, FIG. 10b, FIG. 10c, FIG. 10d is a range-Doppler two-dimensional plot of a simulated statistical energy distribution in an embodiment; wherein, FIG. 10a is a front-side view total blur energy distribution (dB normalization) and FIG. 10b is a large squint total blur energy distribution (dB normalization); fig. 10c is a front side coupled blur energy (dB) and fig. 10d is a large squint coupled blur energy (dB).
Detailed Description
As shown in fig. 5, the method for evaluating the fuzzy comprehensive performance of the strabismus-based SAR system comprises the following steps:
s1: according to parameters of SAR satellite platform position information (instantaneous coordinates and platform height), SAR antenna attitude (antenna array face installation angle), satellite platform speed, satellite attitude information (roll angle, pitch angle and yaw angle) and SAR antenna beam two-dimensional scanning angle (antenna coordinate system, pitch scanning angle and azimuth scanning angle), establishing a satellite-ground geometrical relation model of a satellite-borne SAR system under any squint angle, and calculating to obtain parameter information of instantaneous Doppler frequency, instantaneous distance and instantaneous incidence angle at any position in an imaging scene;
s2: carrying out fuzzy classification on any position in the scene according to the instantaneous Doppler frequency, the instantaneous distance and the instantaneous incidence angle parameter information of any position in the scene; determining the range of Doppler frequency and the range of diagonal distance of a target scene according to SAR imaging set resolution and breadth information, and determining the range of Doppler frequency and the range of diagonal distance corresponding to a target scene area and each fuzzy area;
s3: based on the satellite-ground geometric model and scene skew information and incidence angle information, respectively calculating corresponding target scenes, different fuzzy scenes and further calculating corresponding backscattering coefficients; respectively calculating pattern gain information of corresponding target scenes and different fuzzy scenes based on the two-dimensional antenna pattern gain;
s4: respectively calculating energy intensities corresponding to a corresponding target scene and different fuzzy scenes based on the antenna pattern gain, the inclined distance range and the backscattering coefficient; and calculating the fuzzy ratio indexes of different fuzzes of any squint angle space-borne SAR system according to the definition of the fuzzy ratio.
Further, the step S1 includes:
s11: grid division is carried out on an imaging scene, scene coordinate information is established, and the instantaneous height of the satellite platform is combined according to scene coordinates in the imaging sceneDetermining the current position star-to-ground instantaneous downview angle +.>；
S12: satellite-to-earth instantaneous viewing angle according to current positionDetermining the current coordinate star-to-earth instantaneous angle of incidence +.>：
，
wherein ,is the earth radius;
s13: satellite-to-earth instantaneous viewing angle according to current positionAnd the current coordinate star-to-earth instantaneous angle of incidence +.>Determining the corresponding skew of the current coordinate>：
，
S14: determining instantaneous moment coordinate point according to the instantaneous moment SAR satellite position and satellite platform speedTime Doppler frequency；
，
wherein ,for the instantaneous speed of the satellite relative to the current coordinate point, +.>For the instantaneous skew of the satellite relative to the current coordinate point, vector multiplication +.>Representing the instantaneous relative velocity of the satellite and the coordinate point.
Further, the step S2 includes:
s21: determining the corresponding slant range of the SAR target scene according to the imaging breadth or the angle range of the lower viewing angle required by the SAR systemThe value range-> and />, wherein />For imaging the proximal diagonal of the swath,for imaging breadth far-end slant distance, satisfy:
，
s22: beam center squint angle set according to SAR systemAzimuth resolution->Determining the Doppler center frequency of the target scene>And corresponding Doppler bandwidth->And determining the Doppler frequency corresponding to the target scene>Is defined in the following range:
，
s23: marking coordinate positions in the imaging scene, which satisfy the range of the corresponding diagonal distances of S21 and S22 and the range of the Doppler frequency, as target scenes;
s24: according to the pulse transmitting frequency PRF set by the SAR system, determining the range of the range distance and the Doppler frequency corresponding to any fuzzy scene area:
，
，
wherein ,represents the aliasing number (azimuth) of the fuzzy Doppler spectrum, of the Doppler spectrum>Representing the number of blurred distance-to-scene aliases (distance-to) and +.>Is->Doppler frequency of order bearing ambiguity, +.>Is->Step distance blur diagonal;
s25: and (3) classifying the fuzzy regions of the non-target scene region according to the range of the slope distance and the Doppler frequency corresponding to any fuzzy scene region in the step (S24): will beIs marked as azimuth ambiguous region, willIs marked as distance-blurred region, +.>Is marked as a coupled ambiguous region.
Further, the step S3 includes:
s31: inquiring and obtaining model parameters corresponding to the imaged ground object types by combining the imaged ground object typesValues, noted as:
，
in the formula ,calculating model parameter values for the scattering intensity;
in the L-band (radar system carrier frequency)Satisfy->) For bare ground detection, for example, it +.>The value is +.>；
S32: corresponding to the satellite-ground instantaneous incident angle according to any coordinate point of the scene in S12Combining scattering model parameters corresponding to different ground objects in different frequency bands in S31>Value, obtain electromagnetic back scattering intensity empirical reference value +.>The unit is dB:
，
wherein exp () represents an exponential function based on a natural constant e;
s33: converting the radar coordinate system to the antenna coordinate system for any coordinate of the scene in S1, and according to the directional parameters corresponding to the coordinatesAnd transmit/receive gain based on a priori two-dimensional antenna pattern> and />Obtaining the receiving and transmitting gain intensity of the two-dimensional antenna pattern corresponding to any coordinate of the scene> and />。
Further, the step S4 includes:
s41: receiving and transmitting gain strength combined with two-dimensional antenna pattern and />Corresponding to the target scene in S21, skew +.>Doppler frequency corresponding to the target scene in S22 +.>Calculating the energy intensity of the main signal of the target scene +.>：
，
wherein ,is of oblique distance and is->Is the back scattering intensity;
s42: similarly, the two-dimensional antenna pattern receiving and transmitting gain is combined, and the fuzzy signal energy intensity corresponding to different fuzzy areas, namely the azimuth fuzzy intensity, is calculated according to the fuzzy classification result in S25Distance blur intensity->Coupling ambiguity intensity->：
，
，
，
wherein ,the slant distance of the 0 th order distance blur, namely the slant distance corresponding to the main signal area, +.>The Doppler frequency which is the 0 th order azimuth ambiguity, namely the Doppler frequency corresponding to the main signal area; />Corresponding incidence angle values for the fuzzy regions;
s43: further, when SAR system index design is performed, the fuzzy strength is usually adoptedEnergy intensity of main signal of target scene +.>Ratio calculation blur ratio +.>：
，
Obtaining a corresponding fuzzy performance evaluation index fuzzy ratio: azimuth blur ratio AASR, distance blur ratio RASR, coupling blur ratio CASR, and total blur ratio ASR.
The following description of the embodiments of the present invention is provided to facilitate understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and all the inventions which make use of the inventive concept are protected by the spirit and scope of the present invention as defined and defined in the appended claims to those skilled in the art.
Taking X-band resolution of 1.5m/60km for example, large squint stripe imaging simulation, system parameters are shown in Table 1.
TABLE 1
，
By using the method provided by the invention, the gain of the antenna pattern, the pitch history and the pitch history coordinates correspond to the incident angles, the total fuzzy energy of the system is analyzed and calculated, the difference of the front-side view SAR system and the large squint SAR system on the coupling fuzzy term is given, and the effectiveness of the method provided by the invention is verified.
In the embodiment shown in FIG. 6a, FIG. 6b is a front side view and a side viewThe large squint SAR system corresponds to an antenna pattern projection result. For a large squint SAR system, due to the introduction of squint angle, radar beams are distorted in a single dimension on ground projection, and an antenna pattern of the radar beams is shifted in a distance direction. FIG. 7a, FIG. 7b, FIG. 8a, FIG. 8b and FIG. 9a, FIG. 9b are front side view and +.>The large squint SAR system corresponds to a range-Doppler energy intensity distribution map of each order of fuzzy area; FIG. 10a, FIG. 10b, FIG. 10c and FIG. 10d are the corresponding front side view and +.>The energy distribution contrast diagram of the total fuzzy energy of the large squint SAR system in the range Doppler domain can be seen that the corresponding coupling fuzzy energy of the positive squint SAR system is extremely small, the energy of the part is negligible, and the conventional method is directly adoptedAlmost all fuzzy energy can be analyzed by a distance and azimuth two-dimensional fuzzy analysis method; on the contrary, the corresponding coupling fuzzy energy of the large squint SAR system is larger and cannot be ignored, and the problem of total energy deficiency exists on the basis of the conventional distance and azimuth two-dimensional fuzzy analysis method. />
Claims (5)
1. The fuzzy comprehensive performance evaluation method for the satellite-borne strabismus SAR system is characterized by comprising the following steps of:
s1: establishing a satellite-ground geometric relation model of a satellite-borne SAR system under the condition of any squint angle according to SAR satellite platform position information, SAR antenna gesture, satellite platform speed, satellite gesture information and SAR antenna beam two-dimensional scanning angle parameters, and calculating to obtain parameter information of instantaneous Doppler frequency, instantaneous distance and instantaneous incidence angle at any position in an imaging scene;
s2: carrying out fuzzy classification on any position in an imaging scene according to the instantaneous Doppler frequency, the instantaneous distance and the instantaneous incidence angle parameter information of any position in the scene; determining a value range of Doppler frequency and a value range of a diagonal distance of a target scene according to SAR imaging set resolution and breadth information, and determining a Doppler frequency range and a diagonal range corresponding to a target scene area and each fuzzy area;
s3: based on the satellite-ground geometric model and imaging scene oblique distance information and incidence angle information, respectively calculating corresponding target scenes and backscattering coefficients corresponding to different fuzzy scenes; respectively calculating antenna pattern gains corresponding to the target scene and different fuzzy scenes based on the two-dimensional antenna pattern gains;
s4: respectively calculating energy intensities corresponding to a corresponding target scene and different fuzzy scenes based on the antenna pattern gain, the inclined distance range and the backscattering coefficient; and calculating the fuzzy ratio indexes of different fuzzes of any squint angle space-borne SAR system according to the definition of the fuzzy ratio.
2. The method for evaluating the fuzzy comprehensive performance of the strabismus-based SAR system according to claim 1, wherein said step S1 comprises:
s11: for imaging fieldThe scene is subjected to grid division, scene coordinate information is established, and the instantaneous height of the satellite platform is combined according to the scene coordinates in the imaging sceneDetermining the current position star-to-ground instantaneous downview angle +.>；
S12: satellite-to-earth instantaneous viewing angle according to current positionDetermining the current coordinate star-to-earth instantaneous angle of incidence +.>：
，
wherein ,is the earth radius;
s13: satellite-to-earth instantaneous viewing angle according to current positionAnd the current coordinate star-to-earth instantaneous angle of incidence +.>Determining the corresponding skew of the current coordinate>：
，
S14: determining instantaneous moment coordinate point according to instantaneous moment SAR satellite position and satellite platform speedDoppler frequency；
，
wherein ,for the instantaneous speed of the satellite relative to the current coordinate point, +.>For the instantaneous skew of the satellite relative to the current coordinate point, vector multiplication +.>Representing the instantaneous relative velocity of the satellite and the coordinate point.
3. The method for evaluating the fuzzy comprehensive performance of the strabismus-based SAR system according to claim 2, wherein said step S2 comprises:
s21: determining the corresponding slant range of the SAR target scene according to the imaging breadth or the angle range of the lower viewing angle required by the SAR systemThe value range-> and />, wherein />For imaging the proximal diagonal of the swath,for imaging breadth far-end slant distance, satisfy:
，
s22: beam center squint angle set according to SAR systemAzimuth resolution->Determining the Doppler center frequency of the target scene>And corresponding Doppler bandwidth->And determining the Doppler frequency corresponding to the target scene>Is defined in the following range:
，
s23: corresponding to the target scene meeting S21 in the imaging sceneDoppler frequency corresponding to the target scene of S22>The coordinate position of the value range of (2) is marked as a target scene;
s24: determining the corresponding slant distance of any fuzzy scene area according to the pulse transmitting frequency PRF set by the SAR systemAnd Doppler frequency->Is defined in the following range:
，
，
wherein ,fuzzy Doppler spectrum aliasing number representing azimuth, < >>Fuzzy distance direction scene aliasing number representing distance direction, +.>Is->Doppler frequency of order bearing ambiguity, +.>Is->The slant distance of the step distance blur;
s25: according to the corresponding slant distance of any blurred scene area in S24And Doppler frequencyTo classify the non-target scene area into a fuzzy area: will->Is marked as azimuth ambiguous area, +.>Is marked as a distance blurred region, willIs marked as a coupled ambiguous region.
4. The method for evaluating the fuzzy synthetic performance of an on-board squint SAR system according to claim 3, wherein said step S3 comprises:
s31: inquiring and acquiring scattering model parameters corresponding to the imaged ground object types by combining the imaged ground object typesValues, noted as:
，
in the formula ,calculating model parameter values for the scattering intensity;
s32: corresponding to the satellite-ground instantaneous incident angle according to any coordinate point of the scene in S12Combining scattering model parameters corresponding to different ground objects in different frequency bands in S31>Value, obtain electromagnetic back scattering intensity empirical reference value +.>The unit is dB:
，
wherein exp () represents an exponential function based on a natural constant e;
s33: converting the radar coordinate system to the antenna coordinate system for any coordinate of the scene in S1, and according to the directional parameters corresponding to the coordinatesAnd transmit/receive gain based on a priori two-dimensional antenna pattern> and />Obtaining the receiving and transmitting gain intensity of the two-dimensional antenna pattern corresponding to any coordinate of the scene> and />。
5. The method for evaluating the fuzzy synthetic performance of an on-board squint SAR system according to claim 4, wherein said step S4 comprises:
s41: receiving and transmitting gain strength combined with two-dimensional antenna pattern and />According to the corresponding skew of the target scene in S21Doppler frequency corresponding to the target scene in S22 +.>Calculating the energy intensity of the main signal of the target scene：
，
wherein ,is of oblique distance and is->Is the back scattering intensity;
s42: combining the receiving and transmitting gains of the two-dimensional antenna pattern, and calculating the fuzzy signal energy intensity azimuth fuzzy intensity corresponding to different fuzzy areas according to the fuzzy classification result in S25Distance blur intensity->Coupling ambiguity strength：
，
，
，
wherein ,the slant distance of the 0 th order distance blur, namely the slant distance corresponding to the main signal area, +.>The Doppler frequency which is the 0 th order azimuth ambiguity, namely the Doppler frequency corresponding to the main signal area; />Corresponding incidence angle values for the fuzzy regions;
s43: when SAR system index design is performed, fuzzy strength is usedEnergy intensity of main signal of target scene +.>Is calculated as the ratio of (2) fuzzy ratio->：
，
Sequentially obtaining corresponding fuzzy performance evaluation index fuzzy ratios according to the above steps: azimuth blur ratio AASR, distance blur ratio RASR, coupling blur ratio CASR, and total blur ratio ASR.
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