High-orbit SAR self-adaptive beam position design method

Abstract

The invention discloses a self-adaptive wave position design method for a high-orbit SAR (Synthetic Aperture Radar). The self-adaptive wave position design method comprises the following steps: step 1, determining an imaging mode, a wave position, a polarization mode, a satellite position at a current orbit moment, a satellite attitude, an antenna installation azimuth angle, an antenna installation pitch angle and an antenna imaging wave position scanning angle; step 2, according to the imaging mode, determining a transmitting pulse width, and setting a maximum duty ratio and a minimum duty ratio; 3, determining the maximum available PRF, the image fuzziness and the system sensitivity at the current orbit moment according to the maximum duty ratio and the minimum duty ratio; 4, determining whether to update the PRF according to the image ambiguity and the system sensitivity; step 5, calculating to obtain radar echo starting time and echo window length; and step 6, returning to the step 1 at the moment of entering the next track. According to the method, different PRFs can be adaptively selected according to different track positions, so that adaptive adjustment of radar parameters is realized.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and specifically relates to a high-orbit SAR adaptive beam position design method. The method is applicable to the system beam position design of large elliptical orbit SAR, satellite-borne, missile-borne, and airborne high-squint SAR. Background Art

[0002] The countries with strong research foundation in spaceborne SAR abroad are mainly the United States, Germany, Canada, Italy, Japan, etc. The typical low-Earth orbit spaceborne SAR systems currently in orbit include the United States' "Long Lacrosse" SAR satellite, Canada's Radarsat-1 and Radarsat-2, the German Space Agency (DLR)'s TerraSAR X / TanDEM-X, Italy's Cosmo-Skymed, the European Space Agency's Envisat, ERS1 / 2, Sentinel-1, Japan's ALOS and ALOS-2, etc. In addition to these countries, Russia, Israel, South Korea, India and other countries are also vigorously developing spaceborne SAR technology. my country has also successfully launched a number of synthetic aperture radar satellites.

[0003] System beam position design is an important and critical part of spaceborne SAR. The beam position is closely related to image quality and system performance. Therefore, the beam position design is one of the important tasks of the top-level design of spaceborne SAR. At present, the beam position design of low-orbit spaceborne SAR mainly selects the pulse repetition frequency based on the constraints of transmission pulse shielding, distance and azimuth ambiguity. Later, as the SAR resolution increased, the factors considered in the beam position design also increased accordingly.

[0004] Nanjing Institute of Electronic Technology has analyzed the constraints on the wave position parameters of spaceborne SAR due to the high speed of low-orbit satellite SAR, the large fluctuations in orbital altitude and ground altitude, and the wave position parameters designed for fixed observation positions cannot be applied globally. Then, an adaptive calculation method for the global wave position parameters of spaceborne SAR was proposed. However, this method focuses on the wave position calculation method given by the changes in satellite orbital altitude and ground elevation, and does not focus on the adjustment of radar parameters and wave position due to changes in orbital speed, and does not provide the criteria and specific criteria for wave position changes.

[0005] Yu Ze and others from Beijing University of Aeronautics and Astronautics proposed a method for designing the beam position of a space-borne phased array synthetic aperture radar, analyzing the factors that constrain the beam position design, especially the fuzzy performance of the phased array system, and clarifying the relationship between the fuzzy performance and the system parameters. However, this method cannot solve the problem that the radar parameters and beam positions need to be adjusted due to changes in orbital velocity and the existence of range migration effects, and it also does not provide the criteria and specific criteria for beam position changes. Summary of the invention

[0006] The present invention proposes a high-orbit SAR adaptive beam position design method to solve the problem that radar parameters need to be adjusted due to orbital velocity changes and range migration effects.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A high-orbit SAR adaptive beam position design method specifically comprises the following steps:

[0009] Step 1, determine the imaging mode, wave position, polarization mode, satellite position at the current orbital time, satellite attitude, antenna installation azimuth angle, antenna installation pitch angle and antenna imaging wave position scanning angle;

[0010] Step 2, determine the transmit pulse width according to the imaging mode, and set the maximum duty cycle and the minimum duty cycle;

[0011] Step 3, determining the maximum available PRF, image ambiguity and system sensitivity at the current orbital moment according to the maximum duty cycle and the minimum duty cycle;

[0012] Step 4: compare the image blur and system sensitivity obtained in step 3 with the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment. If the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment decrease by more than a preset threshold compared with the current image blur and system sensitivity, then update the PRF of the system imaging according to the maximum available PRF obtained in step 31; otherwise, keep the PRF of the system imaging consistent with the maximum available PRF at the previous orbital moment.

[0013] Step 5: Determine the minimum angle of incidence and the maximum angle of incidence of the observation scene according to the satellite attitude at the current orbital time, the antenna installation azimuth and pitch angle, and the antenna imaging wave position scanning angle; calculate the minimum slant range and the maximum slant range of the observation scene according to the satellite position at the current orbital time; finally, calculate the radar echo start time and the echo window length according to the minimum angle of incidence, the maximum angle of incidence, the minimum slant range and the maximum slant range of the observation scene, and return the calculation success mark;

[0014] Step 6, enter the next orbital moment and return to step 1.

[0015] Furthermore, in step 2, the maximum duty cycle is 15% and the minimum duty cycle is 4%.

[0016] Furthermore, step 3 specifically includes the following sub-steps:

[0017] Step 31, determining the maximum available PRF according to the maximum duty cycle set in step 2;

[0018] Step 32, calculating the image blur according to the maximum available PRF obtained in step 31 and the polarization mode determined in step 1;

[0019] Step 33, determine whether the image blur and system sensitivity simultaneously meet the imaging index requirement of better than -20dB. If not, reduce the current maximum duty cycle by 1%, repeat steps 31 and 32 until the maximum duty cycle is less than the minimum duty cycle set in step 2, then return the calculation failure flag, save the maximum available PRF, image blur and system sensitivity at the current orbital moment, and then go to step 4; if both the image blur and system sensitivity meet the imaging index requirements, go directly to step 4.

[0020] Further, the operation of step 31 is: while satisfying the following two equations, determine the maximum available PRF under the maximum duty cycle constraint set in step 2:

[0021]

[0022] in:

[0023] R min —Minimum slant range within synthetic aperture time;

[0024] R max —Maximum slant range within synthetic aperture time;

[0025] c—speed of light, 3×10 8 m / s;

[0026] H L —The distance from the platform to the sub-satellite point;

[0027] T p - pulse width;

[0028] T g —The time width of the guard band before and after the transmit pulse;

[0029] T w-nadir — Sub-satellite point echo duration;

[0030] m,n—natural numbers, and m≠n.

[0031] Since the orbital parameters of conventional low-orbit SAR are relatively fixed within the entire orbit range, its beam position design is relatively simple, as long as the emission shielding requirements and ambiguity indicators are met. However, the orbital parameters of high-orbit SAR are time-varying within the entire orbit range, and the beam position design is also affected by the orbital altitude, orbital velocity changes, range migration effects, etc., and adaptive beam position design is required to meet system requirements. Compared with the conventional low-orbit SAR berth design method, the method of the present invention comprehensively considers the influence of the high-orbit SAR orbital altitude, orbital velocity changes, range migration effects, ground surface height, etc. on the beam position design, and can adaptively select different PRFs according to different orbital positions, thereby realizing adaptive adjustment of radar parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the maximum available PRF calculation result obtained by the high-orbit SAR adaptive beam position design method of the present invention. DETAILED DESCRIPTION

[0033] The implementation of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0034] The high-orbit SAR adaptive beam position design method provided by the present invention specifically comprises the following steps:

[0035] Step 1: Determine the imaging mode, beam position, polarization mode, satellite position at the current orbital time, satellite attitude, antenna installation azimuth angle, antenna installation elevation angle, and antenna imaging beam position scanning angle. These parameters are determined by satellite system parameters and are known information.

[0036] Step 2: Determine the transmit pulse width Tp according to the imaging mode and set the maximum duty cycle η max % and minimum duty cycle η min % (In this embodiment, the maximum duty cycle is determined by the high-orbit 20m SAR satellite system as η max %, and the minimum duty cycle is 15% and 4% respectively);

[0037] Step 3: Determine the maximum available PRF, image ambiguity and system sensitivity at the current orbital moment based on the maximum duty cycle and minimum duty cycle set in step 2.

[0038] Step 3 specifically includes the following sub-steps:

[0039] Step 31, according to the maximum duty cycle set in step 2, determine the maximum available PRF (Pulse repetition frequency).

[0040] Specifically, the PRF is determined according to the criteria for selecting PRF for high-orbit SAR. The selection criteria are as follows:

[0041] (1) The upper limit of PRF selection must satisfy the range ambiguity, and the lower limit must satisfy the azimuth ambiguity.

[0042] (2) PRF can adapt to the echo window changes caused by range migration.

[0043] According to the above criteria, the influence of range migration caused by the equivalent squint angle on the echo delay must be considered in the high-orbit SAR beam position design. Based on this, in the present invention, the selection of PRF must satisfy the following two equations:

[0044]

[0045] in:

[0046] R min —Minimum slant range within synthetic aperture time;

[0047] R max —Maximum slant range within synthetic aperture time;

[0048] c—speed of light, 3×10 8 m / s;

[0049] H L —The distance from the platform to the sub-satellite point;

[0050] T p - pulse width;

[0051] T g —The time width of the guard band before and after the transmit pulse;

[0052] T w-nadir — Sub-satellite point echo duration;

[0053] m,n—natural numbers, and m≠n;

[0054] While satisfying the above two equations, the maximum available PRF is determined under the maximum duty cycle constraint set in step 2. This operation can ensure the highest system sensitivity (meeting the general indicator requirements of different mode edge values ​​≤-22dB~-28dB);

[0055] Step 32, calculating the image blur according to the maximum available PRF obtained in step 31 and the polarization mode determined in step 1;

[0056] Step 33, determine whether the image fuzziness and system sensitivity simultaneously meet the imaging index requirement of better than -20dB. If not, reduce the current maximum duty cycle by 1%, and repeat steps 31 and 32 until the maximum duty cycle is less than the minimum duty cycle set in step 2, indicating that the available system imaging PRF cannot be searched. At this time, the calculation failure flag is returned, and the maximum available PRF, image fuzziness and system sensitivity at the current orbit time are saved, thereby completing the radar parameter adaptive calculation, and then enter step 4; if both the image fuzziness and system sensitivity meet the imaging index requirements, directly enter step 4;

[0057] Step 4: compare the image blur and system sensitivity obtained in step 3 with the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment (when step 4 is executed for the first time, the value at the previous orbital moment here adopts the initial value stored in the satellite system). If the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment are both lower than the current image blur and system sensitivity by more than a preset threshold (1 dB in this embodiment), then update the PRF of the system imaging (i.e., the maximum available PRF) according to the maximum available PRF obtained in step 31; otherwise, keep the PRF of the system imaging consistent with the maximum available PRF at the previous orbital moment.

[0058] The design idea of ​​the above scheme is: if the maximum available PRF at the previous orbital moment is used at the current moment, and the calculated image ambiguity and system sensitivity index decrease by less than or equal to 1dB, the satellite can accept it, and the PRF of the system imaging is not updated at this time. If the image ambiguity and system sensitivity index decrease by more than 1dB, the satellite cannot accept it, and the PRF of the system imaging is updated to the maximum available PRF obtained in step 31.

[0059] Step 5: Determine the minimum angle of incidence and the maximum angle of incidence of the observation scene according to the satellite attitude at the current orbital time, the antenna installation azimuth and pitch angle, and the antenna imaging wave position scanning angle; calculate the minimum slant range and the maximum slant range of the observation scene according to the satellite position at the current orbital time; finally, calculate the radar echo start time and the echo window length according to the minimum angle of incidence, the maximum angle of incidence, the minimum slant range and the maximum slant range of the observation scene, and return the calculation success mark.

[0060] Step 6, enter the next orbital moment, and return to step 1. This step realizes the calculation of the radar parameters of the next orbital moment (mainly including the maximum available PRF of system imaging, image ambiguity and system sensitivity), thereby realizing the calculation of radar parameters for each orbital moment, and finally completing the high-orbit SAR adaptive wave position design.

[0061] In order to verify the effectiveness of the method of the present invention, the following parameters are selected for simulation experiments.

[0062] Satellite orbit altitude 42164km, orbit inclination 20°, eccentricity 0, perigee argument 88°, true perigee 180°, right side observation, radar antenna downward viewing angle 3°, strip imaging mode, Figure 1 The maximum available PRF calculation results obtained by using the high-orbit SAR adaptive beam position design method of the present invention are given. Figure 1 It can be seen that the PRF value of the high-orbit SAR system can be obtained by using the wave position adaptive calculation, and different wave position diagrams can be obtained by selecting different orbital positions.

Claims

1. A high-orbit SAR adaptive beam position design method, characterized in that: The specific steps include: Step 1, determine the imaging mode, wave position, polarization mode, satellite position at the current orbital time, satellite attitude, antenna installation azimuth angle, antenna installation pitch angle and antenna imaging wave position scanning angle; Step 2, determine the transmit pulse width according to the imaging mode, and set the maximum duty cycle and the minimum duty cycle; Step 3, determining the maximum available PRF, image ambiguity and system sensitivity at the current orbital moment according to the maximum duty cycle and the minimum duty cycle; Step 4: compare the image blur and system sensitivity obtained in step 3 with the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment. If the image blur and system sensitivity corresponding to the maximum available PRF at the previous orbital moment decrease by more than a preset threshold compared with the current image blur and system sensitivity, then update the PRF of the system imaging according to the maximum available PRF obtained in step 31; otherwise, keep the PRF of the system imaging consistent with the maximum available PRF at the previous orbital moment. Step 5: Determine the minimum angle of incidence and the maximum angle of incidence of the observation scene according to the satellite attitude at the current orbital time, the antenna installation azimuth and pitch angle, and the antenna imaging wave position scanning angle; calculate the minimum slant range and the maximum slant range of the observation scene according to the satellite position at the current orbital time; finally, calculate the radar echo start time and the echo window length according to the minimum angle of incidence, the maximum angle of incidence, the minimum slant range and the maximum slant range of the observation scene, and return the calculation success mark; Step 6, enter the next orbital moment and return to step 1.

2. The high-orbit SAR adaptive beam position design method according to claim 1, characterized in that: In step 2, the maximum duty cycle is 15% and the minimum duty cycle is 4%.

3. The high-orbit SAR adaptive beam position design method according to claim 2, characterized in that: Step 3 specifically includes the following sub-steps: Step 31, determining the maximum available PRF according to the maximum duty cycle set in step 2; Step 32, calculating the image blur according to the maximum available PRF obtained in step 31 and the polarization mode determined in step 1; Step 33, determine whether the image blur and system sensitivity simultaneously meet the imaging index requirement of better than -20dB. If not, reduce the current maximum duty cycle by 1%, repeat steps 31 and 32 until the maximum duty cycle is less than the minimum duty cycle set in step 2, then return the calculation failure flag, save the maximum available PRF, image blur and system sensitivity at the current orbital moment, and then go to step 4; If both the image blur and system sensitivity meet the imaging index requirements, go directly to step 4.

4. The high-orbit SAR adaptive beam position design method according to claim 2, characterized in that: The operation of step 31 is to determine the maximum available PRF under the maximum duty cycle constraint set in step 2 while satisfying the following two equations: in: R min —Minimum slant range within synthetic aperture time; R max —Maximum slant range within synthetic aperture time; c—speed of light, 3×10 8 m / s; H L —The distance from the platform to the sub-satellite point; T p - pulse width; T g —The time width of the guard band before and after the transmit pulse; T w-nadir — Sub-satellite point echo duration; m,n—natural numbers, and m≠n.

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