Satellite-borne SAR stripmap mode adaptive system and observation area determination method

Abstract

The present application belongs to the field of SAR radar ground receiving, and relates to a kind of spaceborne SAR strip working mode adaptive system and observation area determination method, a kind of spaceborne SAR strip working mode identification system and observation area determination method, including receiving antenna, SAR radar receiving equipment, electric control adjustment mechanism, lower computer, feed system, power supply, positioning module.The automatic identification of spaceborne SAR strip working state and working mode can be completed on the ground by the operation of the system, and by comparing the parameters collected and the typical signal characteristics under the spaceborne SAR strip working mode, whether the spaceborne SAR is started, whether it is in the strip working mode, and the corresponding observation area can be automatically determined.Meanwhile, based on the determination method of the above adaptive system, the working state and observation area under different spaceborne SAR strip working modes can be continuously, dynamically and real-timely determined.

Description

Technical Field

[0001] This invention belongs to the field of SAR radar ground reception, and relates to an adaptive system for spaceborne SAR strip working mode and a method for determining the observation area. Background Technology

[0002] Synthetic Aperture Radar (SAR) possesses all-weather, all-day detection and imaging capabilities, strong visibility, high resolution, and good anti-jamming ability, making it widely used in the aerospace field. Spaceborne SAR features high-altitude operation, high speed, and freedom from airspace restrictions, while also providing all-day, all-weather Earth observation and imaging capabilities. It can achieve long-duration, wide-area observation and imaging, as well as high-repeatability, high-resolution observation and imaging, making it particularly suitable for observing relatively stationary ground targets. To resolve the contradiction between high range resolution and a wide observation area, spaceborne SAR typically observes the area in only one mode at a time. This is achieved through different pulse compression techniques such as amplitude modulation, frequency modulation, phase modulation, and hybrid modulation. Typical operating modes of spaceborne SAR include strip, scan, strip, wave, high and low incidence angle, and global observation modes. The spaceborne SAR strip operating mode adaptive system is deployed on the ground. It determines whether the spaceborne SAR is working by comparing the received signal in real time with the signal characteristics stored or calculated under the operating state of the spaceborne SAR. Then, based on the received signal characteristics, it quickly determines whether the spaceborne SAR is in strip operating mode, adjusts the working state of the ground receiving system to detect the operating mode of the spaceborne SAR, and further determines the observation area of ​​the spaceborne SAR in strip operating mode.

[0003] SAR is based on different platform carriers, and different influencing factors need to be considered. Spaceborne SAR and airborne SAR have different platform altitudes and speeds, as well as different effects of Earth's rotation and curvature. Therefore, under different platforms, it is necessary to consider the effects of ground clutter spectrum width, range ambiguity, Earth's rotation, Earth's curvature, radio wave propagation, etc. on the echo, and construct different transmitting and receiving units accordingly.

[0004] Currently, research in the field of SAR radar mainly focuses on the analysis and processing of acquired radar signals to obtain parameters such as signal frequency, bandwidth, pulse width, time of arrival, and angle of arrival. There is little research or discussion on the adaptive identification and observation area determination of different SAR radar operating modes under different carriers. The radar signal characteristics differ under different SAR radar operating modes, which determines that the signal values ​​acquired by the ground receiving system for different operating modes will also differ, thus affecting the basis for generating platform control signals. Therefore, adaptive identification and observation area determination of spaceborne SAR strip operating modes has significant practical implications and application value. Summary of the Invention

[0005] In different operating modes, the characteristic quantities of parameters received by the ground signal receiving system differ for spaceborne SAR. The identification method for spaceborne SAR strip operating mode mainly combines the satellite's operational status with the signal parameters and their variation patterns received by the ground receiving system to identify the strip operating status and mode of the spaceborne SAR. The signal characteristic parameters in the spaceborne SAR strip operating mode mainly include signal frequency, modulation pattern, signal amplitude, pulse repetition period, pulse width, signal bandwidth, signal arrival time, signal end time, signal duration, and signal arrival angle. When the signal parameters received by the ground receiving system meet the criteria, it can be determined whether the spaceborne SAR is powered on and whether it is in strip operating mode, and the observation area can be determined based on the above information.

[0006] The technical problem solved by this invention is to provide an adaptive system for a spaceborne SAR strip operating mode. This system is deployed on the ground and possesses capabilities for satellite orbit calculation, radar signal acquisition, operating mode determination, and observation area assessment. First, based on the satellite orbit calculation module, instantaneous situational information between the adaptive system and the satellite is obtained, including the SAR satellite's position at a given moment, its nadir track, transit time, and the elevation and azimuth parameters θ and φ of the spaceborne SAR relative to the ground adaptive system. These parameters are then transmitted to the adaptive system, which converts them into electronic control signals. The control platform adjusts the elevation and azimuth angles to point the antenna at the transiting spaceborne SAR, completing the initial antenna alignment. Second, the system determines whether the transiting spaceborne SAR is operational based on whether a valid spaceborne SAR radar signal has been acquired. If no signal is acquired, the transiting spaceborne SAR is considered not operational. If a signal is acquired, and the signal modulation pattern, pulse width τ, and signal bandwidth B all meet the criteria, the transiting spaceborne SAR is considered operational. Third, after determining that the spaceborne SAR is powered on and operational, the peak power P of the SAR radar is then used as a reference. t Antenna main lobe gain G tVertical slant range R between the receiver and the nadir point of the spaceborne SAR; effective area A of the receiver antenna. r Determine the signal strength P received instantaneously. r With maximum signal strength P rmax Maximum signal strength P rmax Duration Δt and duration judgment threshold δ Δt The relationship between the received signal bandwidth B and the threshold δ for judging the signal bandwidth in the stripe operating mode. B2 Based on the relationship, it is determined whether the overflying spaceborne SAR is in stripe mode. Finally, based on the determined stripe mode, the observation area in the overflying spaceborne SAR stripe mode is calculated according to the satellite's location, the satellite's nadir position, the location of the SAR radar receiving equipment, and the position of the satellite antenna pointing to the ground.

[0007] The technical solution of the present invention is: an adaptive system for spaceborne SAR strip working mode, including a receiving antenna (1), a SAR radar receiving device (2), an electronic control adjustment mechanism (3), a host computer (4), a slave computer (5), a feeding system and a power supply (6), and a positioning module (7). The receiving antenna (1) includes a reflector (8), an antenna mount (9), and a back frame (10). The adjustment mechanism (3) includes an azimuth adjustment mechanism (11) and an elevation adjustment mechanism (12), and is connected to the feeding system and the power supply (6). The back frame (10) is attached to and fixedly connected to the back of the reflector (8), and is movably connected to the elevation adjustment mechanism (12), and is equipped with... An electronic angle meter (13) can detect the angle between the back frame (10) and the horizontal reference plane; the antenna mount (9) is movably connected to the azimuth adjustment mechanism (11) and is equipped with a bus ring (14); the host computer (4) includes an orbit calculation module (15) and is connected to the power supply system and the power supply (6). It can control the receiver standby state and working state according to the detection needs and orbit calculation data, calculate the time for SAR to pass over the local area, and calculate the initial azimuth angle parameter φ and elevation angle parameter θ of the ground receiver receiving antenna according to the overpass time; an electronic angle meter (16) is installed on the antenna mount (9) and can detect the angle between the antenna mount (9) and the vertical reference plane in steady state.

[0008] As a further improvement of the present invention, the SAR radar receiving device (2) includes a receiving device protector (17), a low-noise high-frequency amplifier (18), a mixer (19), a local oscillator (20), an intermediate frequency amplifier (21), a detector (22), and a video amplifier (23). The high-frequency signal collected by the receiving antenna (1) is sent to the mixer (19) after passing through the low-noise high-frequency amplifier (18). The mixer (19) mixes with the equal-amplitude high-frequency voltage generated by the local oscillator (20) to reduce the signal frequency to the intermediate frequency (IF), and then sends it to the intermediate frequency amplifier (21) to amplify and match the intermediate frequency pulse signal to obtain the maximum output signal-to-noise ratio. Finally, after being amplified by the detector (22) and the video amplifier (23), it is sent to the lower computer (5).

[0009] As a further improvement of the present invention, a standby automatic switch (24) is installed between the host computer (4) and the power supply system and power source (6). The track calculation data can be converted into a control signal for the standby automatic switch (24) in the host computer (4), which can control the standby automatic switch (24) to switch the working state of the ground receiving equipment.

[0010] As a further improvement of the present invention, the back frame (10) and the reflective surface (8) are snap-fitted or bolted together, which enables the reflective surface (8) to be quickly removed from the back frame (10).

[0011] As a further improvement of the present invention, the azimuth adjustment mechanism (11) consists of an azimuth seat, a fixed plate, a large cylindrical gear, a small cylindrical gear, an actuator, a tension bolt assembly, and a slider. The large cylindrical gear is fixed on the azimuth seat and locked to the slider in the groove of the fixed plate by the tension bolt assembly. The small cylindrical gear is fixedly installed on the fixed plate and meshes with the large cylindrical gear. The lower part of the small cylindrical gear is connected to the actuator. The actuator drives the small cylindrical gear to rotate, and then drives the large cylindrical gear and the azimuth seat to rotate according to a preset angle through meshing linkage.

[0012] As a further improvement of the present invention, the (12) consists of an upper support ear, a lower support ear, and an electric cylinder. The upper part of the electric cylinder is hinged to the back frame through the upper support ear, and the lower part is hinged to the antenna mount through the lower support ear. The pitch angle is adjusted by the extension and retraction of the actuator.

[0013] As a further improvement of the present invention, (12) is a servo motor and / or a stepper motor.

[0014] As a further improvement of the present invention, the antenna mount (9) includes two electronic levels arranged perpendicularly to each other, which can detect the initial horizontal state of the antenna mount (9).

[0015] As a further improvement of the present invention, the reflective surface (8) is assembled from four panels, which are connected by snap-fit ​​and positioning pins and are fitted and fixed to the back frame (10) to achieve assembly.

[0016] As a further improvement of the present invention, the positioning module (7) is a Beidou module and / or a GNSS module, used to collect the latitude and longitude information of the adaptive system.

[0017] A method for determining the observation area of ​​an adaptive system for spaceborne SAR strip operation mode, comprising the following steps, determines whether the spaceborne SAR is powered on and in strip operation mode by detecting the characteristic values ​​of the spaceborne SAR signal received by the adaptive system, and then determines the observation area.

[0018] Step 1: Input the latitude and longitude information of the adaptive system into the host computer (4);

[0019] Step 2: Obtain the SAR satellite position h, elevation angle parameter θ and azimuth angle parameter φ of the SAR satellite relative to the adaptive system at a certain moment through the orbit calculation module (15) of the host computer (4), and the maximum observation time window [t0, t] of the SAR satellite. g ];

[0020] Step 3: Input the elevation angle parameter θ and azimuth angle parameter φ of the satellite relative to the adaptive system into the lower computer (5) and convert them into electronic control signals and transmit them to the electronic control adjustment mechanism (3) so that the antenna points to the overpassing satellite SAR;

[0021] Step 4: Determine whether the adaptive system has acquired a signal. If no signal has been acquired, proceed to Step 2; if a signal has been acquired, proceed to Step 5.

[0022] Step 5: Determine whether the acquired signal is a linear frequency modulation (LFM) signal. If it is not a LFM signal, proceed to Step 2; if it is a LFM signal, proceed to Step 6.

[0023] Step 6: Set the power-on pulse width judgment threshold δ τ1 Signal bandwidth power-on judgment threshold δ B1 ;

[0024] Step 6.1: Determine whether the acquired pulse width τ meets the power-on pulse width judgment threshold δ. τ1 The setting is that it satisfies equation (1).

[0025] τ≥δ τ1 (1)

[0026] Step 6.2: Determine whether the acquired signal bandwidth B meets the power-on signal bandwidth judgment threshold δ. B1 The setting is that it satisfies equation (2).

[0027] B≥δ B1 (2)

[0028] If equations (1) and (2) are both true, proceed to step 7; otherwise, proceed to step 2.

[0029] Step 7: Let P rmax P represents the instantaneous maximum signal strength acquired. rmin For receiver sensitivity;

[0030] Step 7.1: If the adaptive system is within the maximum observation window [t0, t] of the SAR airborne platform g The instantaneous maximum signal strength P acquired within the [database / infrastructure]. rmax Satisfying equation (3):

[0031] P rmax <P rmin +30dBmiW (3)

[0032] It is then assumed that the main lobe of the transit spaceborne SAR has never reached the ground area where the adaptive system is located, and proceed to step 2;

[0033] Step 7.2: If the adaptive system is within the maximum observation window [t0, t] of the SAR satellite... g The instantaneous signal strength acquired within the [element] satisfies equation (4):

[0034] P rmax ≥P rmin +30dBmiW (4)

[0035] It is then assumed that the main lobe of the overflying spaceborne SAR has reached the ground region where the adaptive system is located, and proceed to step 8;

[0036] Step 8: Set the conditions for determining the working mode of the spaceborne SAR, including the maximum signal strength P. rmax Duration judgment threshold δ Δt The threshold δ for judging the signal bandwidth in striped operating mode B2 The threshold δ for determining the pulse width in strip operating mode τ2 ;

[0037] Step 8.1: Determine the actual measured maximum signal strength P rmax Does the duration Δt satisfy the judgment threshold δ? Δt That is, satisfying equation (5),

[0038] Δt>δ Δt (5)

[0039] Step 8.2: Determine whether the acquired pulse width τ meets the pulse width judgment threshold δ of the strip working mode. τ2That is, satisfying equation (6):

[0040] τ>δ τ1 (6)

[0041] Step 8.3: Determine whether the acquisition bandwidth B meets the signal bandwidth δ of the stripe working mode. B2 That is, satisfying equation (7):

[0042] B>δ B2 (7)

[0043] If equations (5)-(7) are all true, then it is determined that the strip working mode is in progress and proceeds to step 9; otherwise, proceeds to step 2.

[0044] Step 9: Determine the perspective of the strip working mode. Based on the altitude information h of the airborne SAR platform obtained from the host computer (4), determine the position A(x) of the airborne platform. A ,y A ,z A ), the ground trajectory point B(x) of the airborne platform B ,y B ,z B The location of the ground receiving equipment is C(x). C ,y C ,z C The airborne platform antenna points to the ground position D(x). D ,y D ,z D AC is the slant range from the ground receiving equipment to the airborne platform, AD is the direction of the SAR antenna main beam center, BC is the projected length of the slant range on the ground, and BD is the projected length of the beam on the ground.

[0045] Step 9.1: Solve for φ and φ′ based on the above parameters. φ is the angle between the line connecting the ground receiver and the satellite nadir point and the projection of the satellite beam onto the ground. φ′ is the azimuth angle of the satellite relative to the ground receiver. Then φ and φ′ satisfy equation (8).

[0046]

[0047] Step 9.2: Solve Given the angle between AC and AD, calculate the antenna gain in one in-plane angular direction according to equation (11).

[0048]

[0049] In the formula, G(0) is the antenna main lobe gain. Antenna pattern, and The angle deviating from the maximum value of the antenna main lobe can be obtained according to equation (10), and The minimum value satisfies equation (11).

[0050]

[0051] Step 9.3: Solve for θ, then θ is the SAR radar viewpoint, which can be obtained according to equation (12).

[0052]

[0053] Step 10: Calculate the strip width W of the observation area. The range beamwidth is Δθ. φ1 and φ2 can be obtained according to equations (13) and (14). Then, the strip width W of the observation area can be obtained according to equation (15).

[0054] φ1=arcsin[sin(θ+Δθ / 2)(R e +h) / R e ]-θ-Δθ / 2 (13)

[0055] φ2=arcsin[sin(θ-Δθ / 2)(R e +h) / R e ]-θ+Δθ / 2 (14)

[0056] W=R e (φ1-φ2) (15)

[0057] Step 11: Input the strip width W of the observation area. Let S be the area of ​​the observation area and v be the satellite's orbital speed. Then, according to equation (16), the observation area of ​​the spaceborne SAR in strip mode can be calculated:

[0058] S=WvΔt (16)

[0059] Output S and return to step 2.

[0060] The beneficial effects of this invention are as follows: A spaceborne SAR strip operating mode adaptive system and observation area determination method, comprising a receiving antenna, SAR radar receiving equipment, electronic control adjustment mechanism, lower-level computer, feeding system, power supply, and positioning module. Through the operation of this system, the operating status and mode of the spaceborne SAR strip can be automatically identified on the ground. By comparing the collected parameters with typical signal characteristics under the spaceborne SAR strip operating mode, it can automatically determine whether the spaceborne SAR is powered on, whether it is in strip operating mode, and the corresponding observation area. Furthermore, based on the determination method of the aforementioned adaptive system, this invention can continuously, dynamically, and in real-time determine the operating status and observation area under different spaceborne SAR strip operating modes. Attached Figure Description

[0061] Figure 1Spaceborne SAR strip operating mode adaptive system architecture diagram

[0062] Figure 2 Structure diagram of spaceborne SAR radar receiver

[0063] Figure 3 View model diagram of spaceborne SAR strip operation mode

[0064] Figure 4 Flowchart of Spaceborne SAR Strip Operating Mode Status and Observation Area Determination Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] According to one embodiment of the present invention, in combination Figure 1 An adaptive system for spaceborne SAR strip operation mode according to the present invention includes a receiving antenna (1), a SAR radar receiving device (2), an electronic control adjustment mechanism (3), a host computer (4), a slave computer (5), a power supply system and a power source (6), and a positioning module (7). The receiving antenna (1) includes a reflector (8), an antenna mount (9), and a back frame (10). The adjustment mechanism (3) includes an azimuth adjustment mechanism (11) and an elevation adjustment mechanism (12), and is connected to the power supply system and the power source (6). The back frame (10) is attached to and fixed to the back of the reflector (8), and is movably connected to the elevation adjustment mechanism (12), and is equipped with an electronic angle adjustment device. The instrument (13) can detect the angle between the back frame (10) and the horizontal reference plane; the antenna mount (9) is movably connected to the azimuth adjustment mechanism (11) and is equipped with a bus ring (14); the host computer (4) includes an orbit calculation module (15) and is connected to the power supply system and the power supply (6). It can control the receiver standby state and working state according to the detection needs and orbit calculation data, calculate the time for SAR to pass over the local area, and calculate the initial azimuth angle parameter φ and elevation angle parameter θ of the ground receiver receiving antenna according to the overpass time; the antenna mount (9) is equipped with an electronic angle meter (16), which can detect the angle between the antenna mount (9) and the vertical reference plane in steady state.

[0067] According to one embodiment of the present invention, in combination Figure 2The SAR radar receiving device (2) of the spaceborne SAR strip working mode adaptive system of the present invention includes a receiving device protector (17), a low-noise high-frequency amplifier (18), a mixer (19), a local oscillator (20), an intermediate frequency amplifier (21), a detector (22) and a video amplifier (23). The high-frequency signal collected by the receiving antenna (1) is sent to the mixer (19) after passing through the low-noise high-frequency amplifier (18). The mixer (19) mixes with the equal amplitude high-frequency voltage generated by the local oscillator (20) to reduce the signal frequency to the intermediate frequency (IF) and transmits it to the intermediate frequency amplifier (21) to amplify and match the intermediate frequency pulse signal to obtain the maximum output signal-to-noise ratio. Finally, after being amplified by the detector (22) and the video amplifier (23), it is sent to the lower computer (5).

[0068] According to one embodiment of the present invention, in combination Figure 3 , 4 A detection method for a portable ground receiving system used in the above-mentioned spaceborne SAR stripe operating mode includes the following steps:

[0069] Step 1: Input the latitude and longitude information of the adaptive system into the host computer (4);

[0070] Step 2: Obtain the SAR satellite position h, elevation angle parameter θ and azimuth angle parameter φ of the SAR satellite relative to the adaptive system at a certain moment through the orbit calculation module (15) of the host computer (4), and the maximum observation time window [t0, t] of the SAR satellite. g ];

[0071] Step 3: Input the elevation angle parameter θ and azimuth angle parameter φ of the satellite relative to the adaptive system into the lower computer (5) and convert them into electronic control signals and transmit them to the electronic control adjustment mechanism (3) so that the antenna points to the overpassing satellite SAR;

[0072] Step 4: Determine whether the adaptive system has acquired a signal. If no signal has been acquired, proceed to Step 2; if a signal has been acquired, proceed to Step 5.

[0073] Step 5: Determine whether the acquired signal is a linear frequency modulation (LFM) signal. If it is not a LFM signal, proceed to Step 2; if it is a LFM signal, proceed to Step 6.

[0074] Step 6: Set the power-on pulse width judgment threshold δ τ1 =5μs, signal bandwidth power-on judgment threshold δ B1 =10MHz;

[0075] Step 6.1: Determine whether the acquired pulse width τ meets the power-on pulse width judgment threshold δ. τ1 Assume that equation (17) is satisfied, and input simulation data τ = 20 μs.

[0076] τ≥δ τ1 (17)

[0077] Step 6.2: Determine if the acquired signal bandwidth B matches the signal bandwidth threshold set at power-on, i.e., satisfy equation (18). Input simulation data B = 300MHz.

[0078] B≥δ B1 (18)

[0079] If both (18) and (19) are true, proceed to step 7;

[0080] Step 7: Let P rmin = -110dBmW is the receiver sensitivity;

[0081] Step 7.1: Input simulation data within the maximum SAR satellite observation time window [t0, t g = Instantaneous signal strength P acquired within the time frame rmax = -65dBmW, meets the requirements

[0082] P rmax ≥P rmin +30dBmiW (19)

[0083] If condition (19) is met, it is considered that the main lobe of the overpassing spaceborne SAR has reached the ground area where the adaptive system is located, and proceed to step 8;

[0084] Step 8: Set the conditions for determining the working mode of the spaceborne SAR, including the maximum signal strength P. rmax Duration judgment threshold δ Δt =5s, the threshold for judging the signal bandwidth in striped operating mode δ B2 =200MHz, pulse width judgment threshold δ in strip operating mode τ2 =10μs;

[0085] Step 8.1: Input simulation data and actually measure the maximum signal strength P rmax Duration Δt = 8s, that is,

[0086] Δt>δ Δt (20)

[0087] Satisfy equation (20);

[0088] Step 8.2: Input the pulse width τ = 20μs for simulation data acquisition, that is,

[0089] τ>δ τ1 (twenty one)

[0090] Satisfying equation (21);

[0091] Step 8.3: Input simulation data acquisition bandwidth B = 300MHz, that is...

[0092] B>δ B2 (twenty two)

[0093] If equation (22) is satisfied, then it is determined that the strip working mode is in progress and proceeds to step 9;

[0094] Step 9: Determine the viewing angle of the strip working mode. According to the STK data processing module, the altitude information of the SAR satellite is h = 780km, the satellite position is A (0,0,780km), the satellite nadir position is B [0,0,0], the position of the adaptive system is C [390km,675km,0], AC is the slant range from the SAR radar receiving equipment to the satellite, AD is the distance from the center of the SAR antenna main beam to the ground, BC is the projection length of the slant range on the ground, and BD is the projection length of the beam on the ground.

[0095] Step 9.1: Solve for φ and φ′ based on the above parameters. φ is the angle between the line connecting the ground receiver and the satellite nadir point and the projection of the satellite beam onto the ground. φ′ is the azimuth angle of the satellite relative to the ground receiver. φ′=60°, then φ=30, satisfying equation (23).

[0096] φ=90°-φ′,0<φ′≤90° (23)

[0097] Step 9.2: Solve Given the angle between AC and AD, calculate the antenna gain in one in-plane angular direction according to equation (24).

[0098]

[0099] In the formula, G(0) = 55dB is the antenna main lobe gain. Antenna pattern, and Given d = 10m, λ = c / f, f = 7.8GHz, and c is the speed of light, the wavelength λ = 0.038m is derived. The angle of the maximum value can be obtained from equation (25), and... The minimum value satisfies equation (26), thus yielding...

[0100]

[0101] Step 9.3 Solve for θ, then θ is the SAR radar angle. According to equation (27), θ = 43.2°.

[0102]

[0103] Step 10: Calculate the strip width W of the observation area. The range beamwidth is Δθ = 1°. According to equations (28) and (29), φ1 = 42.8° and φ2 = 43.8° can be obtained. According to equation (30), the width of the observation area strip W = 18.6 km can be obtained.

[0104] φ1=arcsin[sin(θ+Δθ / 2)(R e +h) / R e ]-θ-Δθ / 2 (28)

[0105] φ2=arcsin[sin(θ-Δθ / 2)(R e +h) / R e ]-θ+Δθ / 2 (29)

[0106] W=R e (φ1-φ2) (30)

[0107] Step 11: Input the strip width W of the observation area, let S be the area of ​​the observation area, v = 7.9 km / s be the satellite's orbital speed, and the maximum signal strength P. rmax If the duration Δt = 8s, then according to equation (31), the observation area S = 1175km of the spaceborne SAR in strip mode can be calculated. 2 :

[0108] S=WvΔt (31)

[0109] Output S and return to step 2.

[0110] The above description represents a preferred embodiment of the present invention. For those skilled in the art, any changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention, based on the teachings of the present invention, still fall within the protection scope of the present invention.

Claims

1. A method for determining the observation area of a space-borne SAR in stripmap mode, comprising the following steps: Step 1: input the latitude and longitude information of the adaptive system into the upper computer; Step 2: Obtain the satellite position h, the pitch angle parameter and the azimuth angle parameter of the SAR satellite at a certain time, and the maximum over-the-horizon observation time window [t0, t1] of the SAR satellite through the track calculation module of the upper computer and azimuth angle parameter φ of the SAR satellite relative to the adaptive system g ; Step 3: Set the satellite's elevation angle parameters relative to the adaptive system. The azimuth parameter φ is input into the lower-level machine and converted into an electronic control signal, which is then transmitted to the electronic control adjustment mechanism to make the antenna point towards the overpassing spaceborne SAR. Step 4: determine whether the adaptive system has collected signals, if not, go to Step 2; if yes, go to Step 5; Step 5: determine whether the collected signals are linear frequency modulation signals, if not, go to Step 2; if yes, go to Step 6; Step 6: Set the power-on pulse width judgment threshold δ τ1 , signal bandwidth power-on judgment threshold δ B1 ; Step 6.1: Determine whether the collected pulse width τ satisfies the start-up pulse width determination threshold value δ τ1 is set, i.e. satisfies equation (1), τ > δ τ1 (1) Step 6.2: judging whether the acquired signal bandwidth B satisfies the start-up signal bandwidth judging threshold value δ B1 is set, i.e., formula (2) is satisfied, B ≥ δ B1 (2) if both formula (1) and (2) are true, go to Step 7, otherwise go to Step 2; Step 7: Let P rmax P is the instantaneous maximum signal strength collected rmin receiver sensitivity; Step 7.1: If the instantaneous maximum signal strength P g collected by the adaptive system within the maximum air-borne observation time window [t0, t rmax ] of the SAR on-board platform satisfies the formula (3): P rmax <P rmin +30 (dBm / IW) (3) if formula (5)-(7) are all true, it is determined that the space-borne SAR is in stripmap mode, go to Step 9, otherwise go to Step 2; Step 7.2: If the instantaneous signal strength collected by the adaptive system within the SAR satellite maximum airtime observation window [t0, t g ] satisfies equation (4): P rmax ≥P rmin +30(dBmiW) (4) Step 9.1: solve φ and φ' according to the above parameters, φ is the angle between the line connecting the ground receiver and the satellite subsatellite point and the projection of the satellite beam pointing on the ground, φ' is the azimuth angle of the satellite relative to the ground receiver, then φ and φ' satisfy formula (8), Step 8: Set the satellite-borne SAR working mode judgment condition, including the maximum signal strength P rmax Duration judgment threshold δ Δt , strip working mode signal bandwidth judgment threshold δ B2 , strip working mode pulse width judgment threshold δ τ2 ; Step 8.1: judging whether the actually measured maximum signal strength P rmax whether the duration Δt satisfies the judging threshold value δ Δt i.e. whether formula (5) is satisfied, Δt > δ Δt (5) Step 8.2: judging whether the collected pulse width τ satisfies the strip operation mode pulse width judging threshold value δ τ2 i.e., satisfies equation (6): τ > δ τ2 (6) Step 8.3: Determine whether the acquisition bandwidth B satisfies the strip mode signal bandwidth δ B2 i.e. satisfies equation (7): B > δ B2 (7) Step 9.3: solve θ, then θ is the SAR radar viewing angle, according to formula (12), W can be obtained, Step 9: The view angle of the strip mode is determined according to the height information h of the airborne platform of the free-space SAR obtained by the lower computer, the position A(x A ,y A ,z A ) of the airborne platform, the ground track point B(x B ,y B ,z B ) of the airborne platform, the position C(x C ,y C ,z C ) of the ground receiving device, the position D(x D ,y D ,z D ) of the antenna pointing of the airborne platform on the ground, AC is the slant range from the ground receiving device to the airborne platform, AD is the pointing of the main beam center of the SAR antenna, BC is the projection length of the slant range on the ground, and BD is the projection length of the beam on the ground; Step 10: calculate the strip width W of the observation area, the beam width in the range direction is Δθ, then φ1 and φ2 can be obtained according to formula (13) and (14), and the strip width W of the observation area can be obtained according to formula (15), Step 9.2: Solving For the angle between AC and AD, the antenna gain in an in-plane angular direction is calculated according to equation (11) where G(0) is the antenna main lobe gain, antenna pattern, and is the angle of departure from the antenna main lobe maximum. From equation (10), we have The minimum of satisfies equation (11), Step 11: input the strip width W of the observation area, set S as the area of the observation area, and v as the satellite running speed, then the observation area of the space-borne SAR in stripmap mode can be calculated according to formula (16): S = WvΔt (16) output S, and go back to Step 2. φ1= arcsin[sin(θ + Δθ / 2)(R e +h) / R e ]- θ - Δθ / 2 (13) φ2= arcsin[sin(θ - Δθ / 2)(R e +h) / R e ]- θ + Δθ / 2 (14) W = R e (φ1-φ2) (15) The SAR radar receiving device comprises a receiving device protector, a low-noise high-frequency amplifier, a mixer, a local oscillator, an intermediate frequency amplifier, a detector and a video amplifier, a receiving device protector, a high-frequency signal collected through a receiving antenna, after passing through a low-noise high-frequency amplifier, and then sent to a mixer, the mixer and the local oscillator generate a high-frequency voltage of the same amplitude, the signal frequency is reduced to an intermediate frequency, and the intermediate frequency pulse signal is transmitted to an intermediate frequency amplifier for amplification and matched filtering to obtain the maximum output signal-to-noise ratio, and finally sent to the lower computer after video amplification through the detector and the video amplifier. The standby automatic switch is arranged between the upper computer and the power supply, the orbit calculation data is converted into a control signal of the standby automatic switch in the upper computer, and the standby automatic switch is controlled to convert the working state of the ground receiving device.

2. A system for performing the method of claim 1 for determining the observation region of a space-borne SAR stripmap mode, comprising: The receiving antenna, the SAR radar receiving device, the electric control adjusting mechanism, the upper computer, the lower computer, the feeding system and power supply, and the positioning module are characterized in that the receiving antenna comprises a reflecting surface, an antenna seat and a back frame, the adjusting mechanism comprises an azimuth adjusting mechanism and an elevation adjusting mechanism, and is connected with the feeding system and power supply, the back frame is attached to the back of the reflecting surface and is connected and fixed, is movably connected with the elevation adjusting mechanism, and is provided with an electronic angle gauge for detecting the included angle between the back frame and a horizontal reference surface, the antenna seat is movably connected with the azimuth adjusting mechanism, and is provided with a bus ring, the upper computer comprises a track calculation module, is connected with the feeding system and power supply, controls the standby state and the working state of the receiver according to the detection requirement and the track calculation data, calculates the time of the SAR over-the-top local area, and calculates the initial azimuth angle parameter φ and the elevation angle parameter of the receiving antenna of the ground receiver according to the over-the-top time The antenna seat is provided with an electronic angle gauge for detecting the included angle between the antenna seat and a vertical reference surface in a steady state.

3. The adaptive system for space-borne SAR stripmap mode according to claim 2, characterized in that The back frame and the reflecting surface are connected or bolted, and the reflecting surface can be quickly disassembled from the back frame.

4. The adaptive system for space-borne SAR stripmap mode according to claim 2, characterized in that ​ 5. The adaptive system for space-borne SAR stripmap mode according to claim 2, characterized in that ​ 6. The space-borne SAR stripmap mode adaptive system according to claim 2, wherein The azimuth angle adjusting mechanism is composed of an azimuth seat, a fixed plate, a cylindrical large gear, a cylindrical small gear, an actuating mechanism, a tension bolt assembly and a sliding block.

7. The adaptive system for space-borne SAR stripmap mode according to claim 2, characterized in that The pitch angle adjusting mechanism is composed of an upper supporting lug, a lower supporting lug and an electric cylinder.

8. The space-borne SAR stripmap mode adaptive system of claim 2, wherein The pitch angle adjusting mechanism is a servo motor and / or a stepping motor.

9. The space-borne SAR stripmap mode adaptive system of claim 2, wherein The antenna seat comprises two electronic levels arranged perpendicularly to each other to detect the initial horizontal state of the antenna seat.

10. The space-borne SAR stripmap mode adaptive system of claim 2, wherein The reflecting surface is assembled by four panels, which are connected by bayonets and positioning pins, and are fixed to the back frame to realize assembly.

11. The space-borne SAR stripmap mode adaptive system of claim 2, wherein The positioning module is a Beidou module and / or a GNSS module, which is used to collect the longitude and latitude information of the adaptive system.

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