Method and system for designing sliding bunching working mode of high-orbit SAR (Synthetic Aperture Radar)

Abstract

The invention belongs to the field of synthetic aperture radars, and discloses a high-orbit SAR sliding bunching working mode design method and system. The method comprises the steps that 1, resolution improvement factors of a high-orbit SAR in different orbit satellites are calculated; 2, according to resolution improvement factors of the high-orbit SAR in different orbit satellites, calculating a sliding speed of a sliding bunching mode antenna beam on the ground; 3, calculating the antenna beam angle scanning speed according to the sliding speed of the antenna beam in the sliding bunching mode on the ground; and 4, calculating the scanning angle of the antenna beam according to the observation breadth required by the azimuth. According to the method, the problem that a traditional sliding bunching working mode design and calculation method of the high-orbit SAR fails is solved, the influence of satellite speed time varying and earth rotation on the sliding bunching working mode design of the high-orbit SAR is considered, the precision of the working mode design of an SAR system can be greatly improved, and the method has important application prospects.

Description

Technical Field

[0001] The invention belongs to the field of synthetic aperture radar, and relates to a high-orbit SAR sliding beamforming working mode design method and system. Background Art

[0002] Resolution and imaging width have always been two very important indicators for measuring imaging quality. High resolution can improve the radar's recognition and extraction of fine features of targets, and large imaging width can improve SAR imaging efficiency. They are two important technologies for the development of SAR. At present, the main working modes of SAR include strip mode, scanning mode, TOPSAR mode, sliding beam mode, and beam mode. The resolution obtained by the strip mode is usually relatively low. The scanning mode and TOPSAR mode mainly obtain large mapping strips, and their resolution is lower. The sliding beam mode and beam mode can obtain longer dwell time, so they can obtain higher resolution. In comparison, the sliding beam mode not only obtains high-resolution imaging, but also its azimuth beam is sliding, so it can obtain a longer azimuth mapping strip. For conventional airborne SAR and low-orbit SAR, the factors considered in the sliding beam mode are relatively simple. It only needs to consider the required resolution, mapping strip, etc., and the parameters can be fixed during the full track or full cycle working time. However, for high-orbit SAR, due to the slow flight speed of the satellite and the influence of the earth's rotation, the speed of the satellite's ground beam footprint will be slower than the satellite's flight speed, resulting in a similar sliding beam effect. Therefore, the design of the high-orbit SAR sliding beam mode needs to take into account the resolution improvement effect brought about by the earth's rotation at different orbital positions and the influence of the time-varying orbital speed, so as to optimize the design of the high-orbit SAR sliding beam working mode.

[0003] In the late 1960s, Munson and Walker of the Michigan Institute for the Environment in the United States studied rotating target imaging and started the research on the spotlight mode. The spotlight mode was first applied to the Lacrosse series of satellites in the fine scanning mode; Canada used the spotlight mode as an experimental mode of the Radarsat-2 satellite, increasing the resolution to 1m. In addition, satellite systems such as Germany's TerraSAR-X, Italy's Cosmo-SkyMed, and Israel's TecSAR all use the spotlight mode as a high-resolution working mode. In China, the working mode of the Gaofen-3 satellite launched in 2016 can be selected according to the working scenario, and it also has a sliding spotlight working mode, which can increase the imaging resolution to 1m.

[0004] The patent "A Sliding Beam SAR and Its Implementation Method and Device" provides the maximum scanning angle and antenna size for calculating the sliding beam of low-orbit SAR, and provides the design of the pulse repetition frequency of the sliding beam mode. However, this method is not applicable to the case of high-orbit SAR, and does not provide the specific scanning angular velocity of the antenna beam in the sliding beam mode. The patent "Ultra-High Resolution Agile SAR Satellite Sliding Beam Mode System Parameter Design Method" provides the realization of the sliding beam mode through satellite attitude maneuvers and provides parameter design. However, this method is also aimed at low-orbit SAR satellites. For high-orbit SAR satellites, the adjustment angle is affected by the time-varying satellite speed and the rotation of the earth, and the conventional low-orbit SAR\airborne SAR sliding beam calculation method will fail.

[0005] In summary, at present, the methods related to the sliding beam working mode are mainly aimed at the low-orbit SAR or airborne SAR. This method is not suitable for the high-orbit SAR. Therefore, it is urgent to propose a design method for the sliding beam working mode of the high-orbit SAR. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for designing a sliding beam working mode of a high-orbit SAR, so as to solve the problem that the traditional sliding beam working mode design and calculation method of the high-orbit SAR are invalid.

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

[0008] On the one hand, the present invention provides a method for designing a high-orbit SAR sliding beamforming working mode, which specifically includes the following steps:

[0009] Step 1: Calculate the resolution improvement factor of high-orbit SAR in different orbital satellites. For each orbital satellite, the calculation process of its resolution improvement factor includes the following sub-steps:

[0010] Step 11, calculate the beam ground velocity V using the following formula sg :

[0011]

[0012] in:

[0013] V sg — beam ground speed;

[0014] r s —The position vector of the current orbiting satellite;

[0015] V s —Current orbital satellite speed;

[0016] r t —target position vector;

[0017] β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle,

[0018] Step 12: Calculate the beam footprint velocity V of the current orbit satellite on the ground based on the beam ground velocity and the earth's rotation angular velocity. gt ;

[0019] Step 13, calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite, the calculation formula is as follows:

[0020]

[0021] in:

[0022] γ—resolution improvement factor;

[0023] V gt —The current orbit satellite beam footprint speed on the ground;

[0024] Step 2: Based on the resolution improvement factor of high-orbit SAR on different orbit satellites obtained in step 1, according to the given required azimuth resolution ρ a , calculate the sliding speed of the antenna beam on the ground in sliding spotlight mode:

[0025]

[0026] in:

[0027] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0028] ρ a —Azimuth resolution of sliding beam mode;

[0029] V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight;

[0030] D—antenna size;

[0031] γ—resolution improvement factor;

[0032] Step 3: Calculate the antenna beam angular scanning speed based on the sliding speed of the antenna beam on the ground obtained in step 2:

[0033]

[0034] in:

[0035] ω—antenna beam angle scanning speed;

[0036] R—slant distance from antenna to ground scene center;

[0037] Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

[0038] Furthermore, in step 12, the calculation formula of the beam footprint speed of the current orbit satellite on the ground is as follows:

[0039] V gt =V sg -V t

[0040] in:

[0041] V gt —The current orbit satellite beam footprint speed on the ground;

[0042] V t —Angular velocity of the Earth’s rotation.

[0043] Furthermore, in step 4, the scanning angle of the antenna beam is calculated by the following formula:

[0044]

[0045] in:

[0046] W a,eff —The required observation width in azimuth;

[0047] W a —The beam irradiation scene width in the azimuth direction of the beam spot mode,

[0048] λ—wavelength;

[0049] D—antenna size;

[0050] R—slant distance from antenna to ground scene center;

[0051] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0052] V t —Angular velocity of the Earth’s rotation.

[0053] On the other hand, the present invention provides a high-orbit SAR sliding beamforming working mode design system, including the following modules:

[0054] The resolution improvement factor calculation module is used to calculate the resolution improvement factor of high-orbit SAR on different orbital satellites. For each orbital satellite, the calculation process of the resolution improvement factor includes the following steps:

[0055] (1) Calculate the beam ground velocity V using the following formula sg :

[0056]

[0057] in:

[0058] V sg — beam ground speed;

[0059] r s —The position vector of the current orbiting satellite;

[0060] V s —Current orbital satellite speed;

[0061] r t —target position vector;

[0062] β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle,

[0063] (2) According to the beam ground velocity and the Earth's rotation angular velocity, calculate the beam footprint velocity V of the current orbiting satellite on the ground gt ;

[0064] (3) Calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite. The calculation formula is as follows:

[0065]

[0066] in:

[0067] γ—resolution improvement factor;

[0068] V gt —The current orbit satellite beam footprint speed on the ground;

[0069] The ground sliding velocity calculation module is used to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the output of the resolution improvement factor calculation module, and to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the given azimuth resolution ρ a , calculate the sliding speed of the antenna beam on the ground in sliding spotlight mode:

[0070]

[0071] in:

[0072] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0073] ρ a —Azimuth resolution of sliding beam mode;

[0074] V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight;

[0075] D—antenna size;

[0076] γ—resolution improvement factor;

[0077] The antenna beam angle scanning speed calculation module is used to calculate the antenna beam angle scanning speed according to the sliding speed of the sliding beam mode antenna beam on the ground obtained by the ground sliding speed calculation module:

[0078]

[0079] in:

[0080] ω—antenna beam angle scanning speed;

[0081] R—slant distance from antenna to ground scene center;

[0082] Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

[0083] The method and system of the present invention have the following beneficial effects compared with the prior art:

[0084] The existing sliding beam working mode design method is not suitable for the high-orbit SAR sliding beam working mode design. The present invention proposes an accurate high-orbit SAR working mode design method, which takes into account the influence of satellite velocity time variation, earth rotation and azimuth resolution improvement factor on the high-orbit SAR sliding beam working mode design, and can accurately calculate the system parameters of the high-orbit SAR sliding beam working mode, thus solving the problem of high-orbit SAR sliding beam working mode design.

[0085] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 is the high-orbit SAR resolution improvement factor;

[0087] Figure 2 is the sliding speed of the antenna beam on the ground in sliding beam mode;

[0088] Figure 3 is the antenna beam angle scanning speed;

[0089] Figure 4 is the antenna beam scanning angle.

[0090] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0091] Example 1

[0092] This embodiment provides a method for designing a high-orbit SAR sliding beamforming working mode, which specifically includes the following steps:

[0093] Step 1: Calculate the resolution improvement factor of high-orbit SAR on different orbital satellites. For each orbital satellite, the calculation process of the resolution improvement factor of the satellite includes the following sub-steps:

[0094] Step 11, based on the angular velocity of the ground beam being equal to that of the current orbiting satellite, the beam ground velocity V is calculated using the following formula: sg :

[0095]

[0096] in:

[0097] V sg — beam ground speed;

[0098] r s —The position vector of the current orbiting satellite;

[0099] V s —Current orbital satellite speed;

[0100] r t —target position vector; r s 、V s 、r t All are known;

[0101] β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle,

[0102] Step 12, according to the beam ground velocity and the earth's rotation angular velocity, calculate the beam footprint velocity of the current orbit satellite on the ground, the calculation formula is as follows:

[0103] V gt =V sg -V t

[0104] in:

[0105] V gt —The current orbit satellite beam footprint speed on the ground;

[0106] V t — angular velocity of the Earth's rotation;

[0107] Step 13, calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite, the calculation formula is as follows:

[0108]

[0109] Where: γ—resolution improvement factor.

[0110] Step 2: Based on the resolution improvement factor of the high-orbit SAR in different orbits obtained in step 1, and on the basis of the given required azimuth resolution, calculate the sliding speed of the antenna beam in the sliding beamforming mode on the ground.

[0111] The time-varying orbit height change and time-varying Doppler characteristics of high-orbit SAR cause the particularity of the working mode design. For example, the resolution improvement factor is different at different orbital positions, and the special orbital characteristics cause the azimuth Doppler characteristics to change with time, thus causing the image resolution to change with different Doppler characteristics in different imaging modes.

[0112] Azimuth resolution of sliding beam mode ρ a The expression is as follows:

[0113]

[0114] in,

[0115]

[0116] Therefore, given the required azimuth resolution ρ a On this basis, the present invention calculates the sliding speed of the antenna beam in the sliding beam mode on the ground by the following formula:

[0117]

[0118] in:

[0119] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0120] ρ a —The azimuth resolution of the sliding beam mode is known;

[0121] V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight;

[0122] D—antenna size;

[0123] γ—resolution improvement factor;

[0124] Step 3: Based on the sliding speed of the antenna beam in the sliding beam mode on the ground obtained in step 2, the antenna beam angular scanning speed is calculated according to the effective distance of the satellite.

[0125] Specifically, the calculation formula for the antenna beam angle scanning speed is as follows:

[0126]

[0127] in:

[0128] ω—antenna beam angle scanning speed;

[0129] R—slant distance from the antenna to the center of the ground scene, that is, the effective distance of the satellite;

[0130] Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

[0131] First, the analysis is as follows: Assume that the scanning angle range of the antenna beam is θ∈[θ start ,θ end ], and define the scanning angle of the antenna beam as Δθ = θ end -θ start , then the total width of the azimuth imaging scene is:

[0132]

[0133] in, is the width of the beam scene in the azimuth direction of the spotlight mode, λ is the wavelength, D is the antenna size, and R is the slant distance from the antenna to the center of the ground scene. It can be seen that the azimuth imaging area of ​​the sliding spotlight mode is wider than that of the spotlight mode. However, in this imaging scenario, the width of the area that is fully illuminated by the azimuth beam is:

[0134]

[0135] From the above formula, we can know that the required observation width W in azimuth is a,eff Based on this, the scanning angle of the antenna beam can be calculated by the following formula:

[0136]

[0137] in:

[0138] W a,eff —The required observation width in azimuth;

[0139] W a —The width of the scene illuminated by the beam in the azimuth direction of the beam spotlight mode;

[0140] λ—wavelength;

[0141] D—antenna size;

[0142] R—slant distance from antenna to ground scene center;

[0143] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0144] V t —Angular velocity of the Earth’s rotation.

[0145] In order to verify the feasibility and effectiveness of the proposed method, the following parameters are selected for simulation verification.

[0146] The satellite orbit altitude is 42164km, the orbit inclination is 20°, the eccentricity is 0°, the perigee argument is 88°, the true anomaly is 180°, the right side observation, the carrier frequency is 1.25GHz, the radar antenna downward viewing angle is 3°, the antenna aperture is 20m, the azimuth resolution is 0.5m, and the azimuth mapping zone of the sliding beam working mode is 1000km. The simulation verification is carried out according to the method of the present invention, and the calculation results are as follows Figures 1 to 4 As shown. Among them, Figure 1 is the resolution improvement factor of the high-orbit SAR corresponding to step 1, Figure 2 is the sliding speed of the antenna beam in sliding beamforming mode on the ground corresponding to step 2, Figure 3 is the antenna beam angle scanning speed corresponding to step 3, Figure 4 is the scanning angle of the antenna beam corresponding to step 4. It can be seen from the above figure that the design of the sliding beam mode of the high-orbit SAR satellite needs to take into account the resolution improvement effect brought about by the rotation of the earth at different orbital positions and the influence of the time-varying orbital velocity. Its full-orbit parameters keep changing with the time of passing the perigee, that is, the sliding beam mode parameters of the high-orbit SAR satellite are time-varying values. However, for conventional airborne SAR and low-orbit SAR, the parameters of the sliding beam mode are fixed during the full orbit or full cycle working time, that is, a straight line. It can be seen that the traditional sliding beam mode design method is not applicable to high-orbit SAR satellites. Therefore, the high-orbit SAR sliding beam working mode design method provided by the present invention solves the problem of failure of the traditional sliding beam working mode design and calculation method of the high-orbit SAR.

[0147] Example 2

[0148] This embodiment provides a high-orbit SAR sliding beamforming working mode design system, including the following modules:

[0149] The resolution improvement factor calculation module is used to calculate the resolution improvement factor of high-orbit SAR on different orbital satellites. For each orbital satellite, the calculation process of the resolution improvement factor includes the following steps:

[0150] (1) Calculate the beam ground velocity V using the following formulasg :

[0151]

[0152] in:

[0153] V sg — beam ground speed;

[0154] r s —The position vector of the current orbiting satellite;

[0155] V s —Current orbital satellite speed;

[0156] r t —target position vector;

[0157] β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle,

[0158] (2) According to the beam ground velocity and the Earth's rotation angular velocity, calculate the beam footprint velocity V of the current orbiting satellite on the ground gt ;

[0159] (3) Calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite. The calculation formula is as follows:

[0160]

[0161] in:

[0162] γ—resolution improvement factor;

[0163] V gt —The current orbit satellite beam footprint speed on the ground;

[0164] The ground sliding velocity calculation module is used to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the output of the resolution improvement factor calculation module, and to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the given azimuth resolution ρ a , calculate the sliding speed of the antenna beam on the ground in sliding spotlight mode:

[0165]

[0166] in:

[0167] V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground;

[0168] ρ a —Azimuth resolution of sliding beam mode;

[0169] V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight;

[0170] D—antenna size;

[0171] γ—resolution improvement factor;

[0172] The antenna beam angle scanning speed calculation module is used to calculate the antenna beam angle scanning speed according to the sliding speed of the sliding beam mode antenna beam on the ground obtained by the ground sliding speed calculation module:

[0173]

[0174] in:

[0175] ω—antenna beam angle scanning speed;

[0176] R—slant distance from antenna to ground scene center;

[0177] Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

[0178] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for designing a high-orbit SAR sliding beamforming working mode, characterized in that: The specific steps include: Step 1: Calculate the resolution improvement factor of high-orbit SAR in different orbital satellites. For each orbital satellite, the calculation process of its resolution improvement factor includes the following sub-steps: Step 11, calculate the beam ground velocity V using the following formula sg : in: V sg — beam ground speed; r s —The position vector of the current orbiting satellite; V s —Current orbital satellite speed; r t —target position vector; β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle, Step 12: Calculate the beam footprint velocity V of the current orbit satellite on the ground based on the beam ground velocity and the earth's rotation angular velocity. gt ; Step 13, calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite, the calculation formula is as follows: in: γ—resolution improvement factor; V gt —The current orbit satellite beam footprint speed on the ground; Step 2: Based on the resolution improvement factor of high-orbit SAR on different orbit satellites obtained in step 1, according to the given required azimuth resolution ρ a , calculate the sliding speed of the antenna beam on the ground in sliding spotlight mode: in: V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground; ρ a —Azimuth resolution of sliding beam mode; V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight; D—antenna size; γ—resolution improvement factor; Step 3: Calculate the antenna beam angular scanning speed based on the sliding speed of the antenna beam on the ground obtained in step 2: in: ω—antenna beam angle scanning speed; R—slant distance from antenna to ground scene center; Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

2. The high-orbit SAR sliding beamforming working mode design method as claimed in claim 1, characterized in that: In step 12, the calculation formula of the beam footprint speed of the current orbit satellite on the ground is as follows: V gt =V sg -V t in: V gt —The current orbit satellite beam footprint speed on the ground; V t —Angular velocity of the Earth’s rotation.

3. The high-orbit SAR sliding beamforming working mode design method as claimed in claim 1, characterized in that: It is characterized in that In step 4, the scanning angle of the antenna beam is calculated by the following formula: in: W a,eff —The required observation width in azimuth; W a —The beam irradiation scene width in the azimuth direction of the beam spot mode, λ—wavelength; D—antenna size; R—slant distance from antenna to ground scene center; V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground; V t —Angular velocity of the Earth’s rotation.

4. A high-orbit SAR sliding beam working mode design system, characterized in that: Includes the following modules: The resolution improvement factor calculation module is used to calculate the resolution improvement factor of high-orbit SAR on different orbital satellites. For each orbital satellite, the calculation process of the resolution improvement factor includes the following steps: (1) Calculate the beam ground velocity V using the following formula sg : in: V sg — beam ground speed; r s —The position vector of the current orbiting satellite; V s —Current orbital satellite speed; r t —target position vector; β—Current orbit satellite position vector r s and the target position vector r t The geocentric angle, (2) According to the beam ground velocity and the Earth's rotation angular velocity, calculate the beam footprint velocity V of the current orbiting satellite on the ground gt ; (3) Calculate the resolution improvement factor of the high-orbit SAR on the current orbit satellite. The calculation formula is as follows: in: γ—resolution improvement factor; V gt —The current orbit satellite beam footprint speed on the ground; The ground sliding velocity calculation module is used to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the output of the resolution improvement factor calculation module, and to calculate the resolution improvement factor of the high-orbit SAR on different orbit satellites according to the given azimuth resolution ρ a , calculate the sliding speed of the antenna beam on the ground in sliding spotlight mode: in: V bg — The sliding speed of the antenna beam in sliding spotlight mode over the ground; ρ a —Azimuth resolution of sliding beam mode; V st - Satellite relative target velocity, which is projected to the orbital altitude and points to the direction of the satellite's flight; D—antenna size; γ—resolution improvement factor; The antenna beam angle scanning speed calculation module is used to calculate the antenna beam angle scanning speed according to the sliding speed of the sliding beam mode antenna beam on the ground obtained by the ground sliding speed calculation module: in: ω—antenna beam angle scanning speed; R—slant distance from antenna to ground scene center; Step 4: Calculate the scanning angle of the antenna beam based on the required observation width in azimuth.

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