A high orbit SAR sliding spotlight working mode design method and system

Abstract

The application belongs to the field of synthetic aperture radar, and discloses a high-orbit SAR sliding spotlight working mode design method and system, which comprises the following steps: step one, calculating the resolution improvement factor of high-orbit SAR in different orbit satellites; step two, calculating the sliding speed of the sliding spotlight mode antenna beam on the ground according to the resolution improvement factor of high-orbit SAR in different orbit satellites; step three, calculating the antenna beam angle scanning speed according to the sliding speed of the sliding spotlight mode antenna beam on the ground; and step four, calculating the scanning angle of the antenna beam according to the observation width required in the azimuth direction. The application solves the problem of invalidation of the traditional sliding spotlight working mode design and calculation method of high-orbit SAR, considers the influence of the time-varying satellite speed and the earth rotation on the high-orbit SAR sliding spotlight working mode design, can greatly improve the precision of the SAR system working mode design, and has important application prospect.

Description

Technical Field

[0001] This invention belongs to the field of synthetic aperture radar and relates to a design method and system for a high-orbit SAR sliding spotting working mode. Background Technology

[0002] Resolution and imaging swath width have always been two crucial indicators for measuring imaging quality. High resolution improves radar's ability to identify and extract fine target features, while a large imaging swath enhances SAR imaging efficiency; these are two essential technologies for SAR development. Currently, the main operating modes of SAR include strip mode, scanning mode, TOPSAR mode, sliding spotting mode, and spotting mode. Strip mode typically achieves relatively low resolution, while scanning and TOPSAR modes, which primarily obtain large mapping swaths, have even lower resolution. Sliding spotting and spotting modes, however, offer longer dwell times, thus achieving higher resolution. Comparatively, sliding spotting mode not only provides high-resolution imaging but also features a sliding azimuth beam, allowing for a longer azimuth mapping swath. For conventional airborne SAR and low-Earth orbit SAR, the factors considered for sliding spotting mode are relatively simple: only the required resolution and mapping swath need to be considered, and the parameters can remain constant throughout the entire orbit or operating cycle. However, for high-orbit SAR, due to the slow satellite flight speed and the influence of the Earth's rotation, the speed of the satellite's ground beam footprint is even slower than the satellite's flight speed, resulting in a sliding beam effect. Therefore, the design of the high-orbit SAR sliding beam mode needs to consider the resolution improvement effect caused by the Earth's rotation at different orbital positions and the time-varying effect of orbital velocity, thereby optimizing the design of the high-orbit SAR sliding beam working mode.

[0003] In the late 1960s, Munson and Walker of the Michigan Environmental Research Institute in the United States studied rotating target imaging, initiating research on spotlight modes. Spotlight modes were first applied to the Lacrosse series satellites in fine-scan mode; Canada used spotlight mode as an experimental mode for its Radarsat-2 satellite, improving resolution to 1 meter. Furthermore, satellite systems such as Germany's TerraSAR-X, Italy's Cosmo-SkyMed, and Israel's TecSAR all use spotlight mode as a high-resolution operating mode. In China, the Gaofen-3 satellite, launched in 2016, can select its operating mode according to the working scenario and also has a sliding spotlight mode, capable of improving imaging resolution to 1 meter.

[0004] The patent "A Sliding Beam SAR and Its Implementation Method and Apparatus" provides the maximum scanning angle and antenna size for calculating sliding beam focusing in low-Earth orbit (LEO) SAR, and gives the design of the pulse repetition frequency for the sliding beam focusing mode. However, this method is not applicable to high-Earth orbit (HEO) SAR, and does not provide the specific scanning angular velocity of the antenna beam in the sliding beam focusing mode. The patent "Ultra-High Resolution Agile SAR Satellite Sliding Beam Focusing Mode System Parameter Design Method" proposes to achieve the sliding beam focusing mode through satellite attitude maneuvering and provides parameter design. However, this method is also for LEO SAR satellites. For HEO SAR satellites, the adjustment angle is affected by the time-varying satellite velocity and the Earth's rotation, rendering conventional LEO / airborne SAR sliding beam focusing calculation methods ineffective.

[0005] In summary, current methods related to the sliding spotting working mode are mainly for low-orbit SAR or airborne SAR, and are not applicable to high-orbit SAR. Therefore, there is an urgent need to propose a design method for the sliding spotting working mode of high-orbit SAR. Summary of the Invention

[0006] The purpose of this invention is to provide a design method and system for the sliding spotting working mode of high-orbit SAR, so as to solve the problem of failure of traditional sliding spotting working mode design and calculation methods for high-orbit SAR.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

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

[0009] Step 1: Calculate the resolution improvement factor for high-orbit SAR satellites in different orbits. For each orbital satellite, the calculation process for 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 velocity;

[0014] r s —The position vector of the satellite in its current orbit;

[0015] V s —Current satellite velocity;

[0016] r t —Target position vector;

[0017] β—Current orbital satellite position vector r s With the target position vector r t The angle between the Earth's core and the Earth's center.

[0018] Step 12: Calculate the beam footprint velocity V of the current orbiting 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 high-orbit SAR for satellites in the current orbit. The calculation formula is as follows:

[0020]

[0021] in:

[0022] γ—resolution improvement factor;

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

[0024] Step 2: Based on the resolution improvement factors of high-orbit SAR satellites in different orbits obtained in Step 1, and according to the given required azimuth resolution ρ a Calculate the sliding speed of the antenna beam in the sliding spotting mode on the ground:

[0025]

[0026] in:

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

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

[0029] V st —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its flight;

[0030] D—Antenna size;

[0031] γ—resolution improvement factor;

[0032] Step 3: Based on the sliding speed of the antenna beam in the sliding focus mode on the ground obtained in Step 2, calculate the antenna beam angle scanning speed:

[0033]

[0034] in:

[0035] ω — antenna beam angle scanning speed;

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

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

[0038] Furthermore, in step 12, the formula for calculating the beam footprint velocity of the current orbiting satellite on the ground is as follows:

[0039] V gt =V sg -V t

[0040] in:

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

[0042] V t —Earth's rotational angular velocity.

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

[0044]

[0045] in:

[0046] W a,eff —The required azimuth swath;

[0047] W a — Width of the scene illuminated by the azimuth beam in the spotlight mode

[0048] λ—wavelength;

[0049] D—Antenna size;

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

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

[0052] V t —Earth's rotational angular velocity.

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

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

[0055] (1) The beam ground velocity V is calculated using the following formula. sg :

[0056]

[0057] in:

[0058] V sg —Beam ground velocity;

[0059] r s —The position vector of the satellite in its current orbit;

[0060] V s —Current satellite velocity;

[0061] r t —Target position vector;

[0062] β—Current orbital satellite position vector r s With the target position vector r t The angle between the Earth's core and the Earth's center.

[0063] (2) Calculate the beam footprint velocity V of the current orbiting satellite on the ground based on the beam ground velocity and the Earth's rotation angular velocity. gt ;

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

[0065]

[0066] in:

[0067] γ—resolution improvement factor;

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

[0069] The ground slip velocity calculation module is used to calculate the resolution improvement factor of high-orbit SAR satellites in different orbits based on the resolution improvement factor output by the resolution improvement factor calculation module, according to the given required azimuth resolution ρ. a Calculate the sliding speed of the antenna beam in the sliding spotting mode on the ground:

[0070]

[0071] in:

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

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

[0074] V st —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its 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 based on the sliding speed of the sliding beam-focusing mode antenna beam on the ground obtained from the ground sliding speed calculation module.

[0078]

[0079] in:

[0080] ω — antenna beam angle scanning speed;

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

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

[0083] The advantages of the method and system of the present invention compared with the prior art are as follows:

[0084] Current methods for designing sliding spotting modes are not suitable for high-orbit SAR sliding spotting modes. This invention proposes a precise design method for high-orbit SAR modes, which considers the influence of time-varying satellite velocity, Earth rotation, and azimuth resolution improvement factors on the design of high-orbit SAR sliding spotting modes. It can accurately calculate the system parameters of high-orbit SAR sliding spotting modes and solve the problem of designing high-orbit SAR sliding spotting modes.

[0085] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

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

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

[0088] Figure 3 This refers to the antenna beam angle scanning speed;

[0089] Figure 4 This represents the antenna beam scanning angle.

[0090] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0091] Example 1

[0092] This embodiment presents a design method for a high-orbit SAR sliding spotting working mode, which specifically includes the following steps:

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

[0094] Step 11: Based on the fact that the angular velocities of the ground beam and the current orbiting satellite are equal, calculate the ground velocity V of the beam using the following formula. sg :

[0095]

[0096] in:

[0097] V sg —Beam ground velocity;

[0098] r s —The position vector of the satellite in its current orbit;

[0099] V s —Current satellite velocity;

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

[0101] β—Current orbital satellite position vector r s With the target position vector r t The angle between the Earth's core and the Earth's center.

[0102] Step 12: Calculate the beam footprint velocity of the current orbiting satellite on the ground based on the beam ground velocity and the Earth's rotation angular velocity. The calculation formula is as follows:

[0103] V gt =V sg -V t

[0104] in:

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

[0106] V t —Earth's rotational angular velocity;

[0107] Step 13: Calculate the resolution improvement factor of high-orbit SAR for satellites in the current orbit. The calculation formula is as follows:

[0108]

[0109] Wherein: γ—resolution improvement factor.

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

[0111] The time-varying orbital altitude and time-varying Doppler characteristics of high-orbit SAR cause unique design considerations for its operating modes. For example, different orbital positions result in different resolution improvement factors, and the special orbital characteristics cause the azimuth Doppler characteristics to change over time, thus causing the image resolution to vary with different Doppler characteristics in different imaging modes.

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

[0113]

[0114] in,

[0115]

[0116] Therefore, given the required azimuth resolution ρ a Based on this, the present invention calculates the sliding velocity of the antenna beam in the sliding focus mode on the ground using the following formula:

[0117]

[0118] in:

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

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

[0121] V st —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its 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 spotting mode obtained in Step 2 on the ground, calculate the antenna beam angle scanning speed according to the satellite's operating distance.

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

[0126]

[0127] in:

[0128] ω — antenna beam angle scanning speed;

[0129] R—the slant distance from the antenna to the center of the ground scene, i.e., the effective range of the satellite;

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

[0131] The analysis is as follows: Let the range of the antenna beam scanning angle be 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, Let λ be the width of the azimuth beam illuminating the scene in the spotlight mode, D be the antenna size, and R be the slant distance from the antenna to the center of the scene on the ground. It can be seen that the sliding spotlight mode has a wider azimuth imaging area than the spotlight mode. However, in this imaging scenario, the width of the region that has undergone complete azimuth beam illumination is:

[0134]

[0135] From the above formula, it can be seen that the required observation swath W in the azimuth direction a,eff Based on this, the scanning angle of the antenna beam can be calculated using the following formula:

[0136]

[0137] in:

[0138] W a,eff —The required azimuth swath;

[0139] W a — Width of the scene illuminated by the azimuth beam in the focused beam mode;

[0140] λ—wavelength;

[0141] D—Antenna size;

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

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

[0144] V t —Earth's rotational angular velocity.

[0145] To verify the feasibility and effectiveness of the proposed method, the following parameters were selected for simulation verification.

[0146] The satellite orbits at an altitude of 42,164 km, with an inclination of 20°, eccentricity of 0°, perigee argument of 88°, true perigee of 180°, right-side look-ahead observation, a carrier frequency of 1.25 GHz, a radar antenna downward viewing angle of 3°, an antenna aperture of 20 m, an azimuth resolution of 0.5 m, and a azimuth mapping zone of 1000 km in sliding beam focusing mode. Simulation verification was performed according to the method of this invention, and the calculation results are as follows... Figures 1-4 As shown. Among them, Figure 1 This represents the resolution improvement factor for the high-orbit SAR corresponding to step 1. Figure 2 This represents the sliding speed of the antenna beam in the sliding focus mode corresponding to step 2 on the ground. Figure 3 This refers to the antenna beam angle scanning speed corresponding to step 3. Figure 4 The scanning angle of the antenna beam corresponding to step 4 is shown in the figure above. It can be seen from the figure that the design of the sliding spotting mode for high-orbit SAR satellites needs to consider the resolution improvement effect caused by the Earth's rotation at different orbital positions and the time-varying effect of orbital velocity. Its full-orbit parameters change continuously with the time of perigee, meaning the sliding spotting mode parameters for high-orbit SAR satellites are time-varying values. However, for conventional airborne SAR and low-orbit SAR, the sliding spotting mode parameters remain fixed throughout the entire orbit or the entire operating period, i.e., a straight line. Therefore, it can be seen that traditional sliding spotting mode design methods are not suitable for high-orbit SAR satellites. Therefore, the high-orbit SAR sliding spotting operating mode design method provided by this invention solves the problem of the failure of traditional sliding spotting operating mode design and calculation methods for high-orbit SAR.

[0147] Example 2

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

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

[0150] (1) The beam ground velocity V is calculated using the following formula.sg :

[0151]

[0152] in:

[0153] V sg —Beam ground velocity;

[0154] r s —The position vector of the satellite in its current orbit;

[0155] V s —Current satellite velocity;

[0156] r t —Target position vector;

[0157] β—Current orbital satellite position vector r s With the target position vector r t The angle between the Earth's core and the Earth's center.

[0158] (2) Calculate the beam footprint velocity V of the current orbiting satellite on the ground based on the beam ground velocity and the Earth's rotation angular velocity. gt ;

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

[0160]

[0161] in:

[0162] γ—resolution improvement factor;

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

[0164] The ground slip velocity calculation module is used to calculate the resolution improvement factor of high-orbit SAR satellites in different orbits based on the resolution improvement factor output by the resolution improvement factor calculation module, according to the given required azimuth resolution ρ. a Calculate the sliding speed of the antenna beam in the sliding spotting mode on the ground:

[0165]

[0166] in:

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

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

[0169] V st —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its 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 based on the sliding speed of the sliding beam-focusing mode antenna beam on the ground obtained from the ground sliding speed calculation module.

[0173]

[0174] in:

[0175] ω — antenna beam angle scanning speed;

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

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

[0178] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A design method for a high-orbit SAR sliding spotting working mode, characterized in that, Specifically, the steps include the following: Step 1: Calculate the resolution improvement factor for high-orbit SAR satellites in different orbits. The calculation process for the resolution improvement factor for each orbital satellite includes the following sub-steps: Step 11: Calculate the beam ground velocity using the following formula. : in: —Beam ground velocity; —The position vector of the satellite in its current orbit; —Current satellite velocity; —Target position vector; —Current orbit satellite position vector With the target position vector The angle between the Earth's core and the Earth's center. ; Step 12: Calculate the beam footprint velocity of the current orbiting satellite on the ground based on the beam ground velocity and the Earth's rotation angular velocity. The calculation formula is as follows: in: —The beam footprint speed of the current orbiting satellite on the ground; —Earth's rotational angular velocity; Step 13: Calculate the resolution improvement factor of high-orbit SAR for satellites in the current orbit. The calculation formula is as follows: ； in: —Resolution improvement factor; —The beam footprint speed of the current orbiting satellite on the ground; Step 2: Based on the resolution improvement factors of high-orbit SAR for satellites in different orbits obtained in Step 1, and according to the given required azimuth resolution... Calculate the sliding speed of the antenna beam in the sliding spotting mode on the ground: in: —The sliding speed of the antenna beam in the sliding focus mode on the ground; —Azimuth resolution of the sliding beam pattern; —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its flight; —Antenna dimensions; —Resolution improvement factor; Step 3: Based on the sliding speed of the antenna beam in the sliding focus mode on the ground obtained in Step 2, calculate the antenna beam angle scanning speed: in: —Antenna beam angle scanning speed; R —Slant distance from the antenna to the center of the ground scene; Step 4: Calculate the antenna beam scanning angle based on the required observation swath width in the azimuth direction. The calculation formula is as follows: in: —The required azimuth swath; — Width of the scene illuminated by the azimuth beam in the spotlight mode ; -wavelength; —Antenna dimensions; R —Slant distance from the antenna to the center of the ground scene; —The sliding speed of the antenna beam in the sliding focus mode on the ground; —Earth's rotational angular velocity.

2. A design system for a high-orbit SAR sliding spotting working mode, 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 for satellites in different orbits. The calculation process for the resolution improvement factor of each orbital satellite includes the following steps: (1) The beam ground velocity is calculated using the following formula. : in: —Beam ground velocity; —The position vector of the satellite in its current orbit; —Current satellite velocity; —Target position vector; —Current orbit satellite position vector With the target position vector The angle between the Earth's core and the Earth's center. ; (2) Calculate the beam footprint velocity of the current orbiting satellite on the ground based on the beam ground velocity and the Earth's rotation angular velocity. The calculation formula is as follows: in: —The beam footprint speed of the current orbiting satellite on the ground; —Earth's rotational angular velocity; (3) Calculate the resolution improvement factor of high-orbit SAR for satellites in the current orbit. The calculation formula is as follows: ； in: —Resolution improvement factor; —The beam footprint speed of the current orbiting satellite on the ground; The ground slip velocity calculation module is used to calculate the resolution improvement factor for high-orbit SAR satellites in different orbits, based on the resolution improvement factor output by the resolution improvement factor calculation module, according to the given required azimuth resolution. Calculate the sliding speed of the antenna beam in the sliding spotting mode on the ground: in: —The sliding speed of the antenna beam in the sliding focus mode on the ground; —Azimuth resolution of the sliding beam pattern; —The satellite's velocity relative to the target, which is projected onto its orbital altitude and points in the direction of its flight; —Antenna dimensions; —Resolution improvement factor; The antenna beam angle scanning speed calculation module is used to calculate the antenna beam angle scanning speed based on the sliding speed of the sliding beam-focusing mode antenna beam on the ground obtained from the ground sliding speed calculation module. in: —Antenna beam angle scanning speed; R —Slant distance from the antenna to the center of the ground scene; Antenna beam scanning angle calculation module: Calculates the antenna beam scanning angle based on the required observation swath width in the azimuth direction. The calculation formula is as follows: in: —The required azimuth swath; — Width of the scene illuminated by the azimuth beam in the spotlight mode ; -wavelength; —Antenna dimensions; R —Slant distance from the antenna to the center of the ground scene; —The sliding speed of the antenna beam in the sliding focus mode on the ground; —Earth's rotational angular velocity.

Images