Synthetic aperture radar maximum range measurement method

Abstract

This invention discloses a method for measuring the maximum effective range of synthetic aperture radar (SAR), comprising the following steps: First, a test flight platform loads a test SAR system and images a specific area and cooperative targets from a predetermined viewing angle; then, based on the imaging results of the test SAR system on the low-scattering feature area and corner reflectors obtained from the flight test, as well as the airborne position information and SAR operating parameters recorded by the test flight platform, the NEσ of the low-scattering feature area in the image is calculated. 0 The distance between the SAR and the low-scattering feature region; finally, based on the obtained data, the SAR antenna pattern, and the NEσ of the SAR system... 0 The design value is used to calculate the maximum effective range of the tested SAR system. This invention enables the predictability of important practical performance characteristics of SAR, is simple and easy to operate, requires no complex calculations, has low computational intensity, and can be effectively applied in engineering practice, thus possessing good value for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of synthetic aperture radar technology, and in particular relates to a method for measuring the maximum effective range of synthetic aperture radar, which can be used in airborne synthetic aperture radar, spaceborne synthetic aperture radar, synthetic aperture radar seeker, etc. Background Technology

[0002] Synthetic Aperture Radar (SAR) is an active Earth observation system that can be mounted on aircraft, satellites, missiles, spacecraft, and other flight platforms to conduct all-weather, 24 / 7 observations. It also possesses a certain degree of ground penetration capability and is widely used in military and civilian fields such as battlefield target reconnaissance, land resource exploration, and geological hazard assessment. Maximum effective range is a crucial system indicator for SAR, reflecting its ability to detect targets at a given distance. It is the result of the combined effects of multiple factors, including radar power, antenna gain, processing gain, and system losses.

[0003] For airborne SAR, spaceborne SAR, and SAR seekers, the SAR system typically requires performance testing via flight testing on a test flight platform before being officially installed on transport aircraft / fighter jets, satellites, missiles, or other platforms. In these flight tests, the maximum effective range of SAR is generally measured using methods borrowed from traditional monopulse radar. This involves placing corner reflectors as cooperative targets in a homogeneous environment such as a concrete floor, and using the SAR's effective range against the corner reflectors to extrapolate the SAR's effective range against a specific RCS target. However, this method ignores the differences between SAR and traditional monopulse radar in target detection and fails to fully explore the SAR's potential effective range.

[0004] Traditional monopulse radar has low range and angular resolution, targets can be treated as point targets, and the detection background is simple. According to the target detection theory in noise, the maximum effective range corresponds to the signal-to-noise ratio under a specific detection probability and false alarm probability. However, SAR has two-dimensional high resolution, and the ground environment of SAR images is complex. For different targets in diverse environments, it is difficult to determine the signal-to-noise ratio corresponding to the maximum effective range of SAR as in traditional monopulse radar. Summary of the Invention

[0005] To address the problem that the maximum effective range measurement results of SAR are easily affected by the target and deployment environment in existing technologies, the purpose of this invention is to provide a method for measuring the maximum effective range of synthetic aperture radar. This method employs a test platform with the tested SAR system in flight, utilizing the flight test results and based on NESO (Neural Scale)... 0 The maximum effective range of SAR under the loading conditions of officially used platforms such as satellites, transport aircraft / fighter jets, and missiles was calculated, NEσ 0It is often used to characterize SAR's ability to detect weak targets, and it is only related to the performance of the SAR system and not to the type of target.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A method for measuring the maximum effective range of synthetic aperture radar includes the following steps:

[0008] S1. The test flight platform loads the SAR system under test and images a specific area and cooperative targets from a predetermined perspective;

[0009] S2. Based on the imaging results of the tested SAR system on the low-scattering feature region and corner reflector obtained from the flight test, as well as the air position information and SAR operating parameters recorded by the test flight platform, calculate the NEσ of the low-scattering feature region in the image. 0 , and the distance between the SAR and the low-scattering feature region; where NEσ 0 This indicates the SAR's ability to detect weak targets.

[0010] S3. Based on the data obtained in step S2, the SAR antenna pattern, and the NEσ of the SAR system... 0 The design value was used to estimate the maximum effective range of the tested SAR system.

[0011] Furthermore, step S1 above includes the following sub-steps:

[0012] Step S1.1: Install the SAR system on the test flight platform and debug it to ensure it is working properly;

[0013] Step S1.2: Using a combination of map-based operations and field surveys, select a large area on the ground with low scattering characteristics; deploy corner reflectors as cooperative targets in the selected area's ground environment, with multiple corner reflectors spaced apart along the azimuth direction;

[0014] Step S1.3: Based on the flight altitude of the test flight platform and the working parameters of the SAR during flight, plan the flight route to ensure that the antenna beam can cover the low scattering feature area and cooperative target selected in step S1.2 during SAR flight.

[0015] Step S1.4: The test flight platform flies along the pre-planned route and operates according to the predetermined working parameters to image the selected area and cooperative targets.

[0016] Furthermore, the azimuth spacing between adjacent corner reflectors is greater than 10 azimuth resolution cells, and the signal-to-noise ratio of a single corner reflector to its background is greater than 20 dB.

[0017] Furthermore, step S2 above includes the following sub-steps:

[0018] Step S2.1: Based on the floating-point SAR single-look intensity image obtained from the flight test in Step S1, the main lobe integral value {DN} is obtained by interpolation of pixels corresponding to multiple corner reflectors in the image. ti} and RCS true value σ i The calibration factor at the location of the corner reflector is calculated according to formula (1).

[0019]

[0020] In the formula, i is the index of the corner reflector;

[0021] R t The distance between the SAR and the corner reflector along the slant range direction; when the distance between the deployment positions of multiple corner reflectors along the range direction is less than or equal to 10 range resolution units, the distance between the SAR and multiple corner reflectors along the slant range direction is considered to be the same.

[0022] θ t θ is the angle between the line of sight of the SAR relative to the corner reflector and the beam centerline; θ is defined as... t A deviation away from the SAR direction is positive, and vice versa is negative;

[0023] Step S2.2: Using the antenna pattern, obtain the calibration factor at the location of the low scattering characteristic region according to formula (2).

[0024]

[0025] In the formula, θ n R n These represent the incident angle and distance of the SAR relative to a selected reference point within a low-scattering feature region;

[0026] G t G r These represent the antenna transmit gain and receive gain, respectively.

[0027] Step S2.3: Using the SAR azimuth sampling interval Δx, range sampling interval Δy, and incident angle θ0, obtain the correction calibration factor at the location of the low scattering feature region according to formula (3).

[0028]

[0029] In the formula, θ0 is the angle between the center line of the antenna beam and the vertical direction;

[0030] Step S2.4: Take a subset of pixels around the reference point within the low scattering feature region and calculate their pixel statistical average. <DN n > Calculate the noise equivalent backscattering coefficient of the low scattering characteristic region according to formula (4).

[0031]

[0032] Furthermore, step S3 above includes the following sub-steps:

[0033] Step S3.1: Utilize the SAR radar equations and NEσ 0 Given the operating parameters of the tested SAR system during flight testing and the operating parameters of the SAR system when installed on a formal use platform, an equivalence relationship is established according to formula (5).

[0034]

[0035] In the formula, Design values ​​for the SAR test subjects when installed on a formal use platform;

[0036] R m This is the maximum effective distance during actual use;

[0037] P tn L sn B n F n f sn f PRFn , λ n V n G tn G rn θ 0n , and P tm L sm B m F m f sm f PRFm , λ m V m G tm G rm θ 0m These represent the peak transmit power, system loss, signal bandwidth, noise figure, range sampling frequency, pulse repetition frequency, operating wavelength, platform speed, antenna transmit gain, receive gain, and incident angle during both flight setup and regular use.

[0038] P tn B n F n f sn f PRFn , λ n L is obtained by measurement using an internal SAR calibration system or standard instruments. sn V was obtained through radiation calibration measurements. n Measured by the positioning equipment of the test flight platform;

[0039] The surface target SAR radar equation is as follows:

[0040]

[0041] In the formula, P s Echo power of surface targets;

[0042] P t This represents the peak power of the SAR transmitter.

[0043] G t (θ), G r (θ) represents the transmit gain and receive gain of the SAR antenna in the target direction, respectively;

[0044] λ is the operating wavelength;

[0045] σ 0 The average backscattering coefficient of a surface target;

[0046] R is the SAR range;

[0047] L s For system losses;

[0048] ψ represents the ground-brushing angle;

[0049] cosψ=sin(θ+θ0), where θ is the angle between the target direction and the center of the antenna beam;

[0050] K s (θ,R) is the scaling factor, which varies with θ and R;

[0051] K(θ,R) is the correction scaling factor;

[0052] The NEσ mentioned 0 This means that the received power is equal to the thermal noise power P. n The backscattering coefficient at that time, i.e.

[0053]

[0054] In the formula, k is the Boltzmann constant;

[0055] T0 is 290k;

[0056] B represents the signal bandwidth;

[0057] F is the noise figure;

[0058] The maximum effective range of the SAR during formal use corresponds to θ. 0m The design value θ for the maximum incident angle 0max θ m It is half the pitch beamwidth;

[0059] Step S3.2: Based on formula (5), further calculate the maximum effective range of the tested SAR system according to formula (8).

[0060]

[0061] Furthermore, in step S3.2 above, the maximum effective range of the tested SAR system obtained according to formula (8) is simplified according to the following two cases:

[0062] Scenario 1: During flight tests and formal use, when the tested SAR system's P... t F, λ, B, f s If the operating parameters and antenna pattern are the same, then formula (8) simplifies to formula (9).

[0063]

[0064] If the SAR transmit power and receive noise figure change significantly between the flight test and the actual use, then formula (9) retains P in formula (6). tn F n P tm With F m ;P tn F n P tm F m Measured by SAR internal calibration system or standard instruments;

[0065] Scenario 2: Based on Scenario 1, if the tested SAR uses velocity tracking mode in both flight tests and formal use, i.e., f PRF =kV, where k is a constant, indicating that the azimuth sampling interval is the same, i.e., V n / f PRFn =V m / f PRFm Formula (9) simplifies to formula (10).

[0066]

[0067] Due to the adoption of the technical solution described above, the present invention has the following advantages:

[0068] This method for measuring the maximum effective range of synthetic aperture radar (SAR) allows the tested SAR system to be mounted on a test flight platform before being installed on a formal operational platform. Based on the results of the flight test, the maximum effective range of the SAR during formal use can be calculated, thus enabling the predictability of the important performance characteristics of the SAR in actual use. During use, only a small number of corner reflectors need to be deployed, and cooperative targets such as water surfaces and concrete platforms with low scattering characteristics should be selected. The operation is simple and easy to implement. It does not require complex calculations, has low computational intensity, and can be effectively applied to engineering practice, thus having good promotion and application value. Attached Figure Description

[0069] Figure 1 This is a flowchart of the synthetic aperture radar maximum effective range measurement method of the present invention;

[0070] Figure 2 This is a test situation diagram of the test flight platform carrying the SAR system;

[0071] Figure 3 This is the SAR antenna pattern in the embodiment;

[0072] Figure 4 It is a corner reflector SAR image;

[0073] Figure 5 It is a SAR image of a region with low scattering characteristics. Detailed Implementation

[0074] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0075] like Figure 1 As shown, a method for measuring the maximum effective range of synthetic aperture radar includes the following steps:

[0076] S1. The test flight platform loads the tested SAR system and images a specific area and cooperative targets from a predetermined perspective; the specific steps are as follows:

[0077] Step S1.1: The SAR system used on platforms such as satellites, transport aircraft / fighter jets, and missiles is installed on test flight platforms such as manned aircraft / unmanned aircraft and is debugged to be working properly;

[0078] Step S1.2: Using a combination of map-based operations and field surveys, select a large area with low scattering characteristics, such as a water surface or a concrete platform, on the ground. Deploy corner reflectors as cooperative targets in the selected area's ground environment. Multiple corner reflectors are deployed at intervals along the azimuth direction to reduce calculation errors. The azimuth interval between adjacent corner reflectors is greater than 10 azimuth resolution cells. The range position of multiple corner reflectors varies slightly according to the terrain. The signal-to-noise ratio of a single corner reflector to its background is greater than 20 dB.

[0079] Step S1.3: Based on the flight altitude of the test flight platform and the working parameters of the SAR during flight, plan the flight route to ensure that the antenna beam can cover the low scattering feature area and cooperative target selected in step S1.2 during SAR flight.

[0080] Step S1.4: The test flight platform flies along the pre-planned route and operates according to the predetermined working parameters to image the selected area and cooperative targets;

[0081] S2. Based on the imaging results of the tested SAR system on the low-scattering feature region and corner reflector obtained from the flight test, as well as the air position information and SAR operating parameters recorded by the test flight platform, calculate the NEσ of the low-scattering feature region in the image. 0 And the distance between the SAR and the low-scattering feature region; the specific steps are as follows:

[0082] Step S2.1: Based on the floating-point SAR single-look intensity image obtained from the flight test in Step S1, the main lobe integral value {DN} is obtained by interpolation of pixels corresponding to multiple corner reflectors in the image. ti} and RCS true value σ i The calibration factor at the location of the corner reflector is calculated according to formula (1).

[0083]

[0084] In the formula, i is the index of the corner reflector;

[0085] R t The distance between the SAR and the corner reflector along the slant range direction; when the distance between the deployment positions of multiple corner reflectors along the range direction is less than or equal to 10 range resolution units, the distance between the SAR and multiple corner reflectors along the slant range direction is considered to be the same.

[0086] θ t θ is the angle between the line of sight of the SAR relative to the corner reflector and the beam centerline; θ is defined as... t A deviation away from the SAR direction is positive, and vice versa is negative;

[0087] Step S2.2: Using the antenna pattern, obtain the calibration factor at the location of the low scattering characteristic region according to formula (2).

[0088]

[0089] In the formula, θ n R n These represent the incident angle and distance of the SAR relative to a selected reference point within a low-scattering feature region;

[0090] G t G rThese represent the antenna transmit gain and receive gain, respectively.

[0091] Step S2.3: Using the SAR azimuth sampling interval Δx, range sampling interval Δy, and incident angle θ0, obtain the correction calibration factor at the location of the low scattering feature region according to formula (3).

[0092]

[0093] In the formula, θ0 is the angle between the center line of the antenna beam and the vertical direction;

[0094] Step S2.4: Take a subset of pixels around the reference point within the low scattering feature region and calculate their pixel statistical average. <DN n > Calculate the noise equivalent backscattering coefficient of the low scattering characteristic region according to formula (4).

[0095]

[0096] S3. Based on the data obtained in step S2, the SAR antenna pattern, and the NEσ of the SAR system... 0 The design value is used to estimate the maximum effective range of the tested SAR system; the specific steps are as follows:

[0097] Step S3.1: Utilize the SAR radar equations and NEσ 0 The definition is given by the working parameters of the tested SAR system during flight tests, and the working parameters of the SAR system when it is installed on a formally used platform such as a satellite, transport aircraft / fighter jet, or missile. An equivalence relationship is established according to formula (5).

[0098]

[0099] In the formula, The design values ​​for the tested SAR when it is installed on a formally used platform such as a satellite, transport aircraft / fighter jet, or missile;

[0100] R m This is the maximum effective distance during actual use;

[0101] P tn L sn B n F n f sn f PRFn , λ n V n G tn G rn θ 0n , and P tm L sm B m F mf sm f PRFm , λ m V m G tm G rm θ 0m These represent the peak transmit power, system loss, signal bandwidth, noise figure, range sampling frequency, pulse repetition frequency, operating wavelength, platform speed, antenna transmit gain, receive gain, and incident angle during both flight setup and regular use.

[0102] P tn B n F n f sn f PRFn , λ n L is obtained by measurement using an internal SAR calibration system or standard instruments. sn V was obtained through radiation calibration measurements. n Measured by the positioning equipment of the test flight platform;

[0103] The surface target SAR radar equation is as follows:

[0104]

[0105] In the formula, P s Echo power of surface targets;

[0106] P t This represents the peak power of the SAR transmitter.

[0107] G t (θ), G r (θ) represents the transmit gain and receive gain of the SAR antenna in the target direction, respectively;

[0108] λ is the operating wavelength;

[0109] σ 0 The average backscattering coefficient of a surface target;

[0110] R is the SAR range;

[0111] L s For system losses;

[0112] ψ represents the ground-brushing angle;

[0113] cosψ=sin(θ+θ0), where θ is the angle between the target direction and the center of the antenna beam;

[0114] K s (θ,R) is the scaling factor, which varies with θ and R;

[0115] K(θ,R) is the correction scaling factor;

[0116] The NEσ mentioned 0 This means that the received power is equal to the thermal noise power P. n The backscattering coefficient at that time, i.e.

[0117]

[0118] In the formula, k is the Boltzmann constant;

[0119] T0 is 290k;

[0120] B represents the signal bandwidth;

[0121] F is the noise figure;

[0122] The maximum effective range of the SAR during formal use corresponds to θ. 0m The design value θ for the maximum incident angle 0max θ m It is half the pitch beamwidth;

[0123] Step S3.2: Based on formula (5), further calculate the maximum effective range of the tested SAR system according to formula (8).

[0124]

[0125] In step S3.2 above, the maximum effective range of the tested SAR system obtained according to formula (8) is simplified according to the following two cases:

[0126] Scenario 1: During flight tests and formal use, when the tested SAR system's P... t F, λ, B, f s If the operating parameters and antenna pattern are the same, then formula (8) simplifies to formula (9).

[0127]

[0128] If the SAR transmit power and receive noise figure change significantly between the flight test and the actual use, then formula (9) retains P in formula (6). tn F n P tm With F m ;P tn F n P tm F m Measured by SAR internal calibration system or standard instruments;

[0129] Scenario 2: Based on Scenario 1, if the tested SAR uses velocity tracking mode in both flight tests and formal use, i.e., f PRF=kV, where k is a constant, indicating that the azimuth sampling interval is the same, i.e., V n / f PRFn =V m / f PRFm Formula (9) simplifies to formula (10).

[0130]

[0131] The implementation of the technical solution of the present invention will be described in detail through the following embodiments.

[0132] This embodiment is a simulation example, and the experimental situation is as follows: Figure 2 As shown. The official platform for the tested SAR was a fighter jet, with an economical cruising speed of 290 m / s and a flight altitude of 10,000 m. The design specifications of the tested SAR included: strip and spotlight imaging modes; an operating center frequency of 5.5 GHz; an adjustable incident angle of 40°–65°; signal bandwidths including 100 MHz, 300 MHz, and 500 MHz; a range sampling frequency of 1.2 times the signal bandwidth; and NEσ. 0 Better than -21dB, antenna pattern as follows Figure 3 As shown, the directions of the transmit and receive antennas are... Figure 1 The range beamwidth was 19.6°, and it featured a pulse repetition frequency velocity tracking mode. The test flight platform was a Y-9 aircraft, with a cruise speed of 160 m / s and a flight altitude of 6000 m. The operating parameters for the tested SAR during the flight test included: a center frequency of 5.5 GHz, an incident angle of 58°, a signal bandwidth of 500 MHz, a range sampling frequency of 600 MHz, a system loss of 10 dB, a pulse repetition frequency setting in velocity tracking mode, and strip imaging.

[0133] The maximum effective range of the tested SAR after being installed on a fighter jet was measured using the method of this invention. The tested SAR adopted strip imaging, with an operating center frequency of 5.5 GHz, an incident angle of 70°, a signal bandwidth of 500 MHz, a range sampling frequency of 600 MHz, and a pulse repetition frequency set in velocity tracking mode. The transmit peak power and receive noise figure were considered to be stable during flight testing and formal use. The system loss after formal use was 12 dB, taking into account transmission attenuation due to clouds and fog.

[0134] Reference Figure 1 The present invention provides a method for measuring the maximum effective range of synthetic aperture radar, which specifically includes the following steps:

[0135] Step S1, refer to Figure 2 The transport aircraft loaded the tested SAR system and imaged a specific area and cooperative targets at an incident angle of 58°; the specific steps were as follows:

[0136] Step S1.1: The fighter jet-borne SAR system was installed on the transport aircraft test flight platform and debugged to ensure normal operation.

[0137] Step S1.2: Select a windless water surface for subsequent NEσ calculation. 0 The low-scattering characteristic area was identified, and five 40cm triangular corner reflectors were deployed on the concrete floor as cooperative targets. The RCS of a single corner reflector was 34.1m. 2 The backscattering coefficient of the cement floor is -10dB, and the signal-to-noise ratio of the corner reflector relative to the background is 25.3.

[0138] Step S1.3: Based on the flight altitude of the Y-9 aircraft, the incident angle of the tested SAR, and the SAR range beamwidth, plan the flight path. The SAR range sampling start time is 58μs. The antenna beam can cover the low scattering feature area and the triangular corner reflector selected in step S1.2.

[0139] Step S1.4: The test flight platform flies along the pre-planned route and operates according to the predetermined working parameters to image the selected low-scattering feature area and the triangular corner reflector.

[0140] Step S2: Based on the images obtained from the flight test of the tested SAR system regarding the low-scattering characteristic region and the corner reflector, respectively, as shown below... Figure 4 and Figure 5 As shown, and based on the airborne position information and SAR operating parameters recorded by the test flight platform, the NEσ of the low-scattering region in the image is calculated. 0 And the distance between SAR and low-scattering feature regions: The specific steps are as follows:

[0141] Step S2.1: Based on the floating-point SAR single-look intensity image obtained from the flight test, such as... Figure 4 As shown, using the main lobe integral value and RCS true value after pixel interpolation corresponding to the five corner reflectors in the image, the calibration factor at the location of the corner reflector is calculated according to the following formula.

[0142]

[0143] Step S2.2: Based on the altitude of the test flight platform, the corner reflector, the low-scattering characteristic region, the location shown in the figure, and the SAR incident angle, obtain θ. t θ n The angles are 52.7036° and 59.0073° respectively, R t R n The m and m are 10315m and 12138m respectively, utilizing Figure 3 The antenna pattern shown, G t (θ t ) and G r (θt The value is -0.7151 dB, G t (θ n ) and G r (θ n The value is -0.0574 dB. The calibration factor at the location of the low scattering characteristic region is obtained according to the following formula.

[0144]

[0145] Step S2.3: The SAR azimuth sampling interval Δx and range sampling interval Δy are 0.25m and 0.086m respectively, and the incident angle θ0 is 58°. The correction calibration factor at the location of the low scattering feature region is obtained according to the following formula.

[0146]

[0147] Step S2.4: Select a 40×40 region around the reference point within the low-scattering region, with an average pixel value of 0.0844. Calculate the noise equivalent backscattering coefficient of the low-scattering region using the following formula.

[0148]

[0149] Step S3: Based on the data obtained in step S2, Figure 3 The SAR antenna pattern shown, and the NEσ of the SAR system 0 The design value was used to estimate the maximum effective range of the tested SAR system when it was officially installed on a fighter jet; the specific steps were as follows:

[0150] Step S3.1: Based on the working parameters of the tested SAR system during the flight test and the working parameters of the SAR system when it is installed on the fighter jet, establish an equivalent relationship according to formula (5);

[0151] Step S3.2: During flight tests and formal use, due to the P of the tested SAR system... t F, λ, B, f s The operating parameters and antenna pattern are the same, and both use velocity tracking mode, based on the given... Design value -21dB, system loss L sm 12dB, the maximum effective range of the SAR during formal use was calculated using the following formula:

[0152]

[0153] The above description is only a preferred embodiment of the present invention and not a limitation thereof. Any equivalent changes and modifications made in accordance with the scope of the present invention without departing from the spirit and scope of the present invention shall be within the scope of patent protection of the present invention.

Claims

1. A method for measuring the maximum effective range of synthetic aperture radar, characterized in that: It includes the following steps: S1. The test flight platform loads the SAR system under test and images the low-scattering feature region and cooperative targets from a predetermined perspective; S2. Based on the imaging results of the tested SAR system on the low-scattering feature region and corner reflector obtained from the flight test, as well as the air position information and SAR operating parameters recorded by the test flight platform, calculate the low-scattering feature region in the image. , and the distance between the SAR and the low-scattering feature region; where, This represents the noise equivalent backscattering coefficient; S3. Based on the data obtained in step S2, the SAR antenna pattern, and the SAR system... Design values ​​were used to estimate the maximum effective range of the tested SAR system. Includes the following sub-steps: Step S3.1: Utilize SAR radar equations and Given the operating parameters of the tested SAR system during flight testing and the operating parameters of the SAR system when installed on a formal use platform, an equivalence relationship is established according to formula (5). （5） In the formula, Design values ​​for the SAR test subjects when installed on a formal use platform; This is the maximum effective distance during actual use; , , , , , , , , , , ,as well as , , , , , , , , , , These represent the peak transmit power, system loss, signal bandwidth, noise figure, range sampling frequency, pulse repetition frequency, operating wavelength, platform speed, antenna transmit gain, receive gain, and angle of incidence, respectively, during flight and during regular use. , , , , , Measured by SAR internal calibration system or standard instruments. Obtained through radiation calibration measurements Measured by the positioning equipment of the test flight platform; , These represent the incident angle and distance of the SAR relative to a selected reference point within a low-scattering feature region; The equation for surface target SAR radar is: （6） In the formula, Echo power of surface targets; This represents the peak transmit power of the SAR. , These are the transmit gain and receive gain of the SAR antenna in the target direction, respectively. The operating wavelength; The average backscattering coefficient of a surface target; This refers to the SAR operating range; For system losses; To wipe the corners of the floor; , The angle between the target direction and the center of the antenna beam. The angle between the center line of the antenna beam and the vertical direction; As the scaling factor, its following , And change; To correct the scaling factor; The SAR azimuth sampling interval; The SAR range sampling interval; The aforementioned This means that the received power equals the thermal noise power. The backscattering coefficient at that time, i.e. （7） In the formula, Boltzmann's constant; It is 290k; For signal bandwidth; Noise figure; The maximum effective range of the SAR during formal use corresponds to Design value for maximum incident angle , It is half the pitch beamwidth; Step S3.2: Based on formula (5), further calculate the maximum effective range of the tested SAR system according to formula (8). （8）。 2. The method for measuring the maximum effective range of synthetic aperture radar according to claim 1, characterized in that: Its steps S1 Includes the following sub-steps: Step S1.1: Install the SAR system on the test flight platform and debug it to ensure it is working properly; Step S1.2: Use a combination of map-based operations and field surveys to select areas with large ground areas and low scattering characteristics; Angular reflectors are deployed as cooperative targets in the selected area's ground environment, with multiple angular reflectors spaced apart along the azimuth direction. Step S1.3: Based on the flight altitude of the test flight platform and the working parameters of the SAR during flight, plan the flight route to ensure that the antenna beam can cover the low scattering feature area and cooperative target selected in step S1.2 during SAR flight. Step S1.4: The test flight platform flies along the pre-planned route and operates according to the predetermined working parameters to image the selected area and cooperative targets.

3. The method for measuring the maximum effective range of synthetic aperture radar according to claim 2, characterized in that: The azimuth spacing between adjacent corner reflectors is greater than 10 azimuth resolution cells, and the signal-to-noise ratio of a single corner reflector to its background is greater than 20 dB.

4. The method for measuring the maximum effective range of synthetic aperture radar according to claim 1, characterized in that: Its step S2 Includes the following sub-steps: Step S2.1: Based on the floating-point SAR single-look intensity image obtained from the flight test in Step S1, the main lobe integral value is obtained by interpolation of the pixels corresponding to multiple corner reflectors in the image. and RCS truth value The calibration factor at the location of the corner reflector is calculated according to formula (1). （1） In the formula, The serial number of the corner reflector; The distance between the SAR and the corner reflector along the slant range direction; when the distance between the deployment positions of multiple corner reflectors along the range direction is less than or equal to 10 range resolution units, the distance between the SAR and multiple corner reflectors along the slant range direction is considered to be the same. The angle between the SAR's line of sight relative to the corner reflector and the beam centerline; defined A deviation away from the SAR direction is positive, and vice versa is negative; Step S2.2: Using the antenna pattern, obtain the calibration factor at the location of the low scattering characteristic region according to formula (2). （2） In the formula, , These represent the incident angle and distance of the SAR relative to a selected reference point within a low-scattering feature region; , These represent the antenna transmit gain and receive gain, respectively. Step S2.3: Utilize SAR azimuth sampling interval Distance sampling interval and angle of incidence The correction calibration factor at the location of the low scattering characteristic region is obtained according to formula (3). （3） Step S2.4: Take a subset of pixels around the reference point within the low scattering feature region and calculate their pixel statistical average. The noise equivalent backscattering coefficient of the low scattering characteristic region is calculated according to formula (4). （4）。 5. The method for measuring the maximum effective range of synthetic aperture radar according to claim 1, characterized in that: In step S3.2, the maximum effective range of the tested SAR system obtained according to formula (8) is simplified according to the following two cases: Scenario 1: During flight tests and formal use, when the tested SAR system... , , , , If the operating parameters and antenna pattern are the same, then formula (8) simplifies to formula (9). （9） If the SAR transmit power and receive noise figure change significantly between the flight test and the actual use, then formula (9) retains the value in formula (6). , , and ; , , , Measured by SAR internal calibration system or standard instruments; Scenario 2: Based on Scenario 1, if the tested SAR uses velocity tracking mode in both flight tests and formal use, i.e. ,in, The fact that it is a constant indicates that the azimuth sampling interval is the same, i.e. Formula (9) simplifies to formula (10). （10）。

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