WO2023209751A1 - Image radar, observation parameter designing device, and radar system - Google Patents

Image radar, observation parameter designing device, and radar system Download PDF

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Publication number
WO2023209751A1
WO2023209751A1 PCT/JP2022/018648 JP2022018648W WO2023209751A1 WO 2023209751 A1 WO2023209751 A1 WO 2023209751A1 JP 2022018648 W JP2022018648 W JP 2022018648W WO 2023209751 A1 WO2023209751 A1 WO 2023209751A1
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observation
satellite
radar
center position
parameter design
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PCT/JP2022/018648
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French (fr)
Japanese (ja)
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正芳 土田
聡 影目
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三菱電機株式会社
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Priority to PCT/JP2022/018648 priority Critical patent/WO2023209751A1/en
Priority to JP2024503810A priority patent/JPWO2023209751A1/ja
Publication of WO2023209751A1 publication Critical patent/WO2023209751A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques

Definitions

  • the disclosed technology relates to an image radar, an observation parameter design device, and a radar system.
  • the image radar and observation parameter design device is a radar that performs imaging, such as a synthetic aperture radar (SAR) mounted on a satellite, and observes the observation target range at a predetermined resolution.
  • Observation parameters for this observation pulse repetition frequency, radar beam scanning angle, etc.
  • the ground station partially transmits the setting information, and the observation control unit mounted on the radar satellite designs the observation parameters and sets the observation.
  • observation methods for satellite-mounted synthetic aperture radar there are several types of observation methods for satellite-mounted synthetic aperture radar, and among them, there is an observation method that scans the radar beam electronically or mechanically as the satellite moves.
  • the spotlight observation method performs observation by constantly irradiating the radar beam onto the observation target area by scanning so that the radar beam is directed at the center of the observation target area.
  • the sliding spotlight observation method performs observation by scanning so that the radar beam is directed farther than the center of the observation target area, thereby slowing down the speed at which the radar beam sweeps over the ground surface.
  • These observation methods combine radar beam scanning and increase the amount of time that objects on the ground are irradiated by the radar beam (equivalent to increasing the angular range in which objects are observed by radar). Improves azimuth resolution.
  • observation parameters including a reference point (referred to here as the beam rotation center position) to specify the radar beam scanning method. It is.
  • Conventional image radar and observation parameter design devices assume that the satellite position at the center time of observation is in the direction of approximately zero Doppler frequency (the so-called zero Doppler frequency corresponds directly to the side) with respect to the center of the observation target area. , setting observation parameters. Under this premise, the observation target area on the earth's surface and the movement range of the satellite in the satellite orbit were approximated to a straight line, and observation parameters were designed based on the approximated observation geometry.
  • FIG. 1 shows an approximate observation geometry using a sliding spotlight observation method as an example.
  • observation parameters are designed based on a triangle formed by the observation start position S s of the satellite, the observation end position S e , and the beam rotation center position R c .
  • the desired azimuth resolution is the distance R 0 of the center position P c of the observation target area with respect to the satellite position S c at the center time of observation, and the distance between the center position P c of the observation target area and the beam rotation center position R c Since this is achieved by the ratio of R1, the beam rotation center position Rc is determined according to the ratio that achieves the desired azimuth resolution. Then, the beam scanning angle necessary to achieve the desired azimuth observation width (determined by the distance to the ground) (for example, Non-Patent Document 1).
  • the observation parameter design of conventional satellite-borne imaging radar is such that the satellite position at the center time of observation is in the direction of zero Doppler frequency with respect to the center of the observation target area, or even if it is in the direction of non-zero Doppler frequency, the angle is a few degrees. Assuming that the observation target area on the earth's surface is a plane, the movement of the satellite in the satellite orbit is approximated as a straight line, and the beam rotation center position where the desired observation performance (azimuth resolution) can be obtained is determined. Based on this, observation parameters are determined.
  • the satellite position at the observation center time may deviate from the vertical direction from the center of the observation target area, and the satellite position may differ from the above satellite position.
  • the assumption no longer holds true observed with the same positional relationship are called "squint observations"
  • the oblique angle called “squint angle" when looking at the center of the observation target area from the satellite at the center time of observation becomes large. Therefore, with the conventional method of determining the beam rotation center position, there is a problem in that it becomes difficult to determine observation parameters that will obtain the desired observation performance.
  • the technology disclosed herein solves the above-mentioned problems, and enables observation parameters that can be designed to obtain the desired observation performance when scanning a radar beam as the satellite moves and observing at a large squint angle.
  • the purpose is to provide design equipment and image radar.
  • the imaging radar according to the disclosed technology is an imaging radar that is mounted on a satellite and performs squint observation using an observation method in which the radar beam (B) is scanned as the satellite moves, and the center position of the observation target area is the radar beam (B).
  • a satellite-side parameter design unit (112) is provided that calculates a beam rotation center position that achieves an azimuth observation width that satisfies design specifications based on the angular velocity across (B).
  • the imaging radar according to the disclosed technology has the above configuration, it is possible to design observation parameters that can obtain the desired observation performance when scanning the radar beam as the satellite moves and observing at a large squint angle. It is.
  • FIG. 1 is an explanatory diagram showing approximate observation geometry using a sliding spotlight observation method as an example.
  • FIG. 2 is a configuration diagram of the radar system according to the first embodiment.
  • FIG. 3 is a flowchart showing processing steps of the radar system according to the first embodiment.
  • FIG. 4 is an explanatory diagram showing the positional relationship between a satellite and an observation target when Squint observation is performed using the sliding spotlight observation method.
  • FIG. 5 is an explanatory diagram showing a method of calculating the angular velocity ( ⁇ str0 ) at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation.
  • FIG. 6 is an explanatory diagram showing a method for calculating an azimuth beam rotation angle that satisfies design specifications.
  • FIG. 2 is a configuration diagram of the radar system according to the first embodiment.
  • the radar system according to the first embodiment includes a radar satellite 100 and a ground station 200.
  • the radar satellite 100 has a radar control section 110 including a satellite-side parameter design section 112.
  • the ground station 200 has an observation planning unit 210 that includes a ground-side parameter design unit 212.
  • the satellite-side parameter design unit 112 and the ground-side parameter design unit 212 are different functional blocks as shown in FIG. 2, the content of the processing that each performs is the same.
  • the name observation parameter design device is used.
  • the radar satellite 100 is an image radar, and may be, for example, a synthetic aperture radar in which a SAR sensor is mounted on a satellite housing.
  • the radar control unit 110 which is a component of the SAR sensor of the radar satellite 100, uses observation parameters designed based on observation commands (C and C are derived from the initials of "Command") transmitted from the ground station 200.
  • the SAR sensor is controlled to irradiate the earth's surface with a radar beam (B is derived from the initial letter "Beam").
  • the radar control unit 110 includes a satellite-side parameter design unit 112, which designs observation parameters for Squint observation on a satellite orbit (O is derived from the initial letter of Orbit).
  • the ground station 200 has an observation planning unit 210 that creates an observation command (C) to be sent to the radar satellite 100.
  • the observation planning unit 210 includes a ground-side parameter design unit 212, which designs observation parameters for Squint observation at the ground station 200.
  • the satellite-side parameter design unit 112 and the ground-side parameter design unit 212 have a function in which one of them independently designs observation parameters, or both of them work together to design observation parameters in observation parameter design for Squint observation. has.
  • FIG. 3 is a flowchart showing processing steps of the radar system according to the first embodiment. More specifically, FIG. 3 shows the satellite-side parameter design unit 112 and the ground-based parameter design unit 112, which design observation parameters when performing observation with a large squint angle (i.e., “squint observation”), which is the purpose of the disclosed technology. 3 shows processing steps of the side parameter design unit 212.
  • the flowchart shown in FIG. 3 is based on the premise that the radar system according to the disclosed technique performs squint observation using the sliding spotlight observation method.
  • FIG. 4 is an explanatory diagram showing the positional relationship between a satellite and an observation target when Squint observation is performed using the sliding spotlight observation method.
  • the technology disclosed herein assumes that the earth shape is a spheroid, the satellite orbit (O) is an ellipse, and the observation geometry is handled in a three-dimensional space.
  • the shape of the earth and the satellite orbit (O) are represented by circles, and the observation geometry is represented on a two-dimensional plane.
  • S sqc represents the satellite position at the observation center time during Squint observation
  • P c represents the center position of the observation target area
  • R sqc represents the beam rotation center position during Squint observation.
  • the satellite moves in a satellite orbit (O) and irradiates a radar beam (B) to the earth (E, E is derived from the initial letter "Earth").
  • Figure 4 shows the satellite position at the observation center time in conventional observation as S c , in order to clarify the difference from the observation geometry of the sliding spotlight observation method, which is not the conventional Squint observation.
  • the beam rotation center position is indicated by R c .
  • the S in Sc which means satellite position
  • the R in Rc which means the center of rotation, is derived from the initial letter of the English word "Rotation.”
  • the subscript C of S c and R c is derived from the initial letter of the English word Center.
  • step ST301 is performed by the observation planning unit 210 of the ground station 200.
  • the observation planning unit 210 sends to the ground-side parameter design unit 212 the center position P c of the observation target area, the satellite position S sqc at the observation center time, the azimuth beam width ⁇ az of the radar beam (B), Preconditions for design such as the desired azimuth observation width Xf of the observation target area are input.
  • the observation planning unit 210 may be programmed to assist the operator of the ground station 200 in inputting the above input items via an input interface.
  • the processing steps after step ST301 are performed by the observation planning unit 210 of the ground station 200.
  • step ST301 is performed by the radar control unit 110 of the radar satellite 100.
  • the radar control unit 110 sends to the satellite-side parameter design unit 112 the center position P c of the observation target area, the satellite position S sqc at the observation center time during Squint observation, and the azimuth beam width of the radar beam (B).
  • ⁇ az and design preconditions such as the desired azimuth observation width X f of the observation target area are input.
  • the radar control unit 110 may be programmed to assist the operator of the radar satellite 100 in inputting the above input items via an input interface.
  • the subscript Sqc of S sqc which means the satellite position at the observation center time during Squint observation, is derived from the first two letters of Squint, which is the English word for Squint, and the initial letter of Center, which is the English word for Squint. do.
  • the processing steps after step ST301 are executed by the radar control unit 110 of the radar satellite 100.
  • Step ST302 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines the satellite position (rear side) S sqb on the satellite orbit (O) that is a predetermined time away from the observation center time during Squint observation and the observation center time.
  • a satellite position (forward side) S sqf that is a predetermined time away from the satellite is temporarily set.
  • the predetermined time is, for example, about 10 to 20 [seconds] of observation time.
  • the subscript sqb of S sqb which means the satellite position (back side), is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of back, which is the English word for backward.
  • the subscript sqf of S sqf which means the satellite position (forward side), is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of forward, which is the English word for Squint.
  • Step ST303 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the angular velocity ⁇ str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation.
  • FIG. 5 is an explanatory diagram showing a method of calculating the angular velocity ⁇ str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation.
  • S sqx shown in FIG. 5 is an arbitrary satellite position on the satellite orbit (O).
  • ⁇ x shown in FIG. 5 is the angle formed by the center position P c of the observation target area at the satellite position S sqx with respect to the zero Doppler direction from the satellite position S sqx .
  • the satellite orbit (O) is given as a prerequisite for designing observation parameters, and the speed of the satellite is uniquely determined by the laws of physics from the altitude of the satellite orbit (O).
  • the value of ⁇ x at the satellite position S sqx can be calculated from the position vector of the satellite position S sqx and the position vector of the center position P c of the observation target area.
  • step ST303 first, the angle of the center position P c of the observation target area between the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O) ⁇ b and ⁇ f (each corresponding to ⁇ x at each satellite position) are calculated. Then, the angular velocity ⁇ str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation is calculated using the difference approximation formula shown in Equation (1).
  • T is the distance between the satellite position (back side) S sqb on the satellite orbit (O) that is a predetermined time away from the observation center time and the satellite position (front side) S sqf that is a predetermined time away from the observation center time. It is a time interval.
  • Step ST304 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 performs iterative calculation to set the beam rotation center position R sqc during Squint observation.
  • this iterative calculation process makes it possible to achieve the desired azimuth resolution on the line segment connecting the satellite position S sqc at the observation center time during Squint observation and the center position P c of the observation target area. This is to find the distance between S sqc and R sqc .
  • the beam rotation center position R sqc that achieves the desired observation performance is determined.
  • Step ST305 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines an initial value as a candidate for the beam rotation center position R sqc as a first step of the iterative calculation.
  • the beam rotation center position R sqc may be determined by gradually changing the distance between the satellite position S sqc and the beam rotation center position R sqc at the observation center time during Squint observation.
  • the most primitive method of iterative calculation is to search for plausible solutions at regular intervals.
  • the candidate for the beam rotation center position R sqc may be made to coincide with the center position P c of the observation target area, for example.
  • the candidates for the beam rotation center position R sqc are updated by, for example, aligning the candidates at the observation center time on a straight line connecting the satellite position S sqc at the observation center time and the center position P c of the observation target area.
  • the distance between the satellite position S sqc and the center position P c of the observation target area may be used as a reference, and the distance may be set at a distance extended by a preset increment.
  • the distance from the satellite position S sqc at the observation center time will be 1.02 times, 1.04 times, 1.06 times, etc. ⁇ , is determined at the position. Performing calculations at regular intervals like this helps identify trends.
  • the search for the beam rotation center position R sqc that satisfies the design specifications may be performed using, for example, a binary search method in which the search is performed from both the side smaller than the solution and the side larger than the solution.
  • the square of the error from the target value (in the case of the disclosed technology, the square of the error between the azimuth resolution of the design specification and the azimuth resolution of the solution candidate) is calculated by calculating the minute change in the solution candidate.
  • Newton's method may be used, in which partial differentiation is performed numerically by , and the search width is changed based on the value of the numerically determined partial differentiation.
  • Step ST306 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground side parameter design unit 212 or the satellite side parameter design unit 112 determines that the center position P c of the observation target area is the radar beam ( Calculate the angular velocity ⁇ str [R sqc ] across B).
  • the disclosed technology defines the angle of the beam rotation center position R sqc from an arbitrary satellite position S sqx on the satellite orbit (O) to the zero Doppler direction as ⁇ x , and calculates the angle of this angular velocity ⁇ str [R sqc ]. Clarify the calculation method.
  • the value of the angle ⁇ x of the beam rotation center position R sqc at the satellite position S sqx can be calculated from the position vector of the satellite position S sqx and the position vector of the beam rotation center position R sqc .
  • step ST306 first, the angle ⁇ , are calculated as ⁇ b and ⁇ f , respectively.
  • the rotational angular velocity ⁇ [R sqc ] of the radar beam (B) is determined by the difference approximation formula shown in Equation (2).
  • the angular velocity ⁇ str [R sqc ] that crosses the radar beam (B) using the current observation method is calculated using equation (3).
  • Step ST307 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 performs strip map observation in which the angular velocity ratio ( ⁇ str [R sqc ]/ ⁇ str0 ) is determined by the azimuth beam width ⁇ az of the radar beam (B). It is determined whether the ratio ⁇ az / ⁇ az0 of the azimuth resolution ⁇ az0 at the time and the desired azimuth resolution ⁇ az given as a precondition for design is equal.
  • the azimuth resolution ⁇ az0 at the time of strip map observation is given by, for example, the following equation (4).
  • ⁇ is the wavelength of radar waves used in radar.
  • step ST307 The determination performed in step ST307 is based on the principle shown below. It is a fact that the azimuth resolution of synthetic aperture radar is determined by the synthetic aperture angle. During strip map observation, the synthetic aperture angle is equivalent to the azimuth beam width. Therefore, in spotlight and sliding spotlight observations that scan the radar beam (B) as the satellite moves, it is possible to increase the synthetic aperture angle and improve the azimuth resolution by scanning the radar beam (B). be exposed.
  • the disclosed technique focuses on the fact that a change in the synthetic aperture angle due to this beam scanning can result in a change in the angular velocity of the radar beam (B).
  • step ST307 it is determined by using the ratio of angular velocities whether or not the desired azimuth resolution has been obtained. If it is determined in step ST307 that the angular velocity ratios are the same, the iterative calculation process is completed. If it is determined that the angular velocity ratios are not the same, the process returns to step ST305 and the iterative calculation process continues.
  • Step ST308 is a processing step performed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines that the beam rotation center position R sqc finally obtained in the iterative calculation process is the desired beam rotation center position, that is, the design specification.
  • Step ST309 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates an azimuth beam rotation angle that satisfies the design specifications.
  • the azimuth beam rotation angle calculated in step ST309 is at the beam rotation center position R sqc that achieves the desired azimuth observation width, that is, the azimuth resolution that satisfies the design specifications.
  • FIG. 6 is an explanatory diagram showing a method of calculating an azimuth beam rotation angle that satisfies the design specifications in step ST309.
  • P b represents the azimuth observation end (backward) of the observation target area
  • P f represents the azimuth observation end (front) of the observation target area.
  • S sqs represents the satellite position at the start of observation
  • S sqe represents the satellite position at the end of observation.
  • the subscript Sqs of S sqs which means the satellite position at the start of observation, is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of start, which is the English word for Squint.
  • the subscript Sqe of S sqe which means the satellite position at the end of observation, is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of end, which is the English word for End.
  • ⁇ sqc represents the beam scanning angle at the satellite position S sqc at the observation center time
  • ⁇ sqs represents the beam scanning angle at the satellite position S sqs
  • ⁇ sqe represents the beam scanning angle at the satellite position S sqe .
  • the beam scanning angles ⁇ sqc , ⁇ sqs , and ⁇ sqe are defined as angles formed by a vector from each satellite position to the beam rotation center position R sqc and a vector in the zero Doppler direction.
  • ⁇ R is the azimuth beam rotation angle at the beam rotation center with respect to the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O).
  • the part shown in the so-called comic balloon in FIG. 6 is an enlarged view of the geometric relationship between the beam rotation center position R sqc and the points P b , P c , and P f on the earth's surface.
  • l b , l c , and l f represent distances between line segments connecting the beam rotation center position R sqc and points P b , P c , and P f , respectively.
  • ⁇ b and ⁇ f represent angles formed by P b -R sqc -P c and P c -R sqc -P f , respectively.
  • the distance L bf between points P b and P f , which are both ends of the observation target area, is given by the following equation (5).
  • X f is the desired azimuth observation width of the observation target area
  • ⁇ az is the azimuth beam width of the radar beam (B)
  • R csq is the distance between the satellite position S sqc and the center position P c of the observation target area at the observation center time. is the distance.
  • step ST309 the line segment length l c is calculated from the respective position vectors of the center position P c of the observation target area and the beam rotation center position R sqc , which have already been determined. Further, the line segment lengths l b and l f are calculated from L ha and the angle ⁇ sqc using the cosine theorem.
  • step ST309 the azimuth beam rotation angle ⁇ b at the beam rotation center position R sqc is calculated from the line segment lengths l b and L ha and the angle ⁇ sqc using the law of sine.
  • the azimuth beam rotation angle ⁇ f at the beam rotation center position R sqc is similarly calculated from l f , L ha , and the angle ⁇ sqc using the law of sine.
  • Step ST310 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the ratio between the azimuth beam rotation angle at the beam rotation center position R sqc and the azimuth beam rotation angle on the satellite orbit (O).
  • the azimuth beam rotation angle ⁇ R at the beam rotation center position R sqc with respect to the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O) is calculated based on the following formula (7).
  • R sqc is the position vector of the beam rotation center position R sqc
  • S sqb is the position vector of the satellite position (rear side) S sqb on the satellite orbit (O)
  • S sqf is the position vector of the satellite position (rear side) on the satellite orbit (O).
  • the position vector of the satellite position (front side) S sqf is represented respectively.
  • the symbol . on the right side of Equation (7) is an operator representing the inner product of vectors. Further, the symbol for the absolute value on the right side of Equation (7) represents the magnitude of the vector.
  • step ST310 an azimuth beam on the satellite orbit (O) is determined from the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O).
  • the rotation angle ⁇ R is calculated based on the following formula (8).
  • step ST310 the ratio angr of the azimuth beam angle on the satellite orbit (O) and at the beam rotation center position is calculated based on the following equation (9).
  • Step ST311 is a processing step performed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the observation time T obs required to achieve the desired azimuth observation width, that is, the observation time T obs that satisfies the design specifications, using the following formula (10 ) Calculated based on
  • the function MAX[] is a function that returns the maximum value among input arguments.
  • m is a coefficient for providing a time margin.
  • Step ST312 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112.
  • the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 starts observation based on the observation time T obs calculated in step ST311 and the satellite position S sqc at the observation center time during Squint observation.
  • the satellite position S sqs at the time of observation and the satellite position S sqf at the end of observation are determined.
  • step ST312 based on the position vector of each satellite position and the position vector of the beam rotation center position R sqc , a beam scanning angle ⁇ sqs at the satellite position S sqs , a beam scanning angle ⁇ sqe at the satellite position S sqe , is required.
  • Step ST313 is a processing step performed by the radar control unit 110.
  • radar control section 110 controls radar satellite 100 to perform observation based on the observation parameters calculated in the processing from step ST301 to step ST312.
  • the disclosed technology does not design observation parameters using observation geometry that approximates the shapes of the satellite orbit (O) and the earth (E) to a straight line. This is done using observational geometry that takes shape into consideration.
  • the disclosed technology enables observation parameter design using an observation method that scans the radar beam (B) as the satellite moves, even in Squint observation where the shape of the satellite orbit (O) and the earth (E) cannot be approximated to a straight line. Therefore, the same observation can be realized.
  • the technology disclosed herein designs observation parameters based on the angular velocity at which the center position of the observation target area crosses the radar beam (B) in an observation method in which the radar beam (B) scans as the satellite moves.
  • the satellite orbit (O) and the shape of the earth (E) can be considered.
  • the beam rotation center position can be designed using, for example, iterative calculation processing.
  • the disclosed technology can calculate with high precision the beam rotation center position that can achieve a desired azimuth resolution even in squint observation.
  • the disclosed technology takes into account the ratio of the beam rotation center position and the rotation angle of the radar beam (B) on the satellite orbit (O), it is possible to achieve the desired azimuth observation width even in Squint observation.
  • the required observation time can be calculated with high precision.
  • the disclosed technology can calculate the rotation angle of the beam rotation center position necessary to achieve a desired azimuth observation width, that is, the rotation angle of the beam rotation center position that satisfies the design specifications, based on the law of cosines and the law of sine. I made it.
  • the observation time required to achieve a desired azimuth observation width can be calculated with a low calculation load.
  • the disclosed technology has industrial applicability because it can be applied, for example, to an image radar such as a synthetic aperture radar in which a SAR sensor is mounted on a satellite housing.

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Abstract

An image radar according to the present disclosure is installed on a satellite, and implements squint observation with an observation method in which a radar beam (B) is scanned together with the movement of the satellite. The image radar comprises a satellite-side parameter designing unit (112) that calculates a beam rotation center position which achieves an azimuth observation width satisfying a design specification on the basis of the angular velocity with which a center position of an observation target region crosses the radar beam (B).

Description

画像レーダ、観測パラメータ設計装置、及びレーダシステムImage radar, observation parameter design device, and radar system
　本開示技術は画像レーダ、観測パラメータ設計装置、及びレーダシステムに関する。 The disclosed technology relates to an image radar, an observation parameter design device, and a radar system.
　画像レーダ及び観測パラメータ設計装置は、衛星に搭載した合成開口レーダ（ＳＡＲ：Ｓｙｎｔｈｅｔｉｃ　Ａｐｅｒｔｕｒｅ　Ｒａｄａｒ）に代表される画像化を行うレーダで、観測対象範囲を所定の分解能で観測する。同観測のための観測パラメータ（パルス繰返し周波数やレーダビームの走査角など）は、地上局の観測立案部で設計し、衛星へ観測コマンドとして送信してレーダ衛星に搭載する観測制御部が観測の設定を行う。地上局からは設定情報を部分的に送信し、レーダ衛星に搭載される観測制御部で観測パラメータを設計し、観測の設定を行う、という態様も考えられる。 The image radar and observation parameter design device is a radar that performs imaging, such as a synthetic aperture radar (SAR) mounted on a satellite, and observes the observation target range at a predetermined resolution. Observation parameters for this observation (pulse repetition frequency, radar beam scanning angle, etc.) are designed by the observation planning department of the ground station, and sent to the satellite as observation commands, which are then sent to the observation control section on board the radar satellite to carry out the observation. Make settings. It is also conceivable that the ground station partially transmits the setting information, and the observation control unit mounted on the radar satellite designs the observation parameters and sets the observation.
　衛星搭載合成開口レーダの観測方式には複数の種類があるが、その内で、衛星の移動と伴にレーダビームを電子的又は機械的に走査する観測方式がある。例えば、スポットライト観測方式は、観測対象領域の中心にレーダビームを指向するように走査することで、観測対象範囲に常にレーダビームを照射して観測を行う。また、スライディングスポットライト観測方式は、観測対象領域の中心よりも遠方にレーダビームを指向するように走査することで、レーダビームが地表を掃引する速度を緩やかにして観測を行う。これら観測方式では、レーダビームの走査を併用し、地表上の物体がレーダビームに照射される時間を長くすることで（物体をレーダで観測する角度範囲を増やすことに相当する）、画像化時のアジマス分解能を向上させる。一方、ＴＯＰＳ（Ｔｈｅ　Ｔｅｒｒａｉｎ　Ｏｂｓｅｒｖａｔｉｏｎ　ｗｉｔｈ　Ｐｒｏｇｒｅｓｓｉｖｅ　Ｓｃａｎｓ）観測方式のように、レーダビームの走査により、レーダビームが地表を掃引する速度を速めて観測を行う方式もある。同方式では、地表を掃引する速度を速めることで観測時間が短くなる分を、エレベーション方向での複数のスキャンに配分することで、エレベーション方向における観測幅を広くする。ただし、地表面の物体がレーダビームに照射される時間が短くなるので、画像化時のアジマス分解能は低下する。 There are several types of observation methods for satellite-mounted synthetic aperture radar, and among them, there is an observation method that scans the radar beam electronically or mechanically as the satellite moves. For example, the spotlight observation method performs observation by constantly irradiating the radar beam onto the observation target area by scanning so that the radar beam is directed at the center of the observation target area. In addition, the sliding spotlight observation method performs observation by scanning so that the radar beam is directed farther than the center of the observation target area, thereby slowing down the speed at which the radar beam sweeps over the ground surface. These observation methods combine radar beam scanning and increase the amount of time that objects on the ground are irradiated by the radar beam (equivalent to increasing the angular range in which objects are observed by radar). Improves azimuth resolution. On the other hand, there is also a method, such as TOPS (The Terrain Observation with Progressive Scans) observation method, in which observation is performed by increasing the speed at which the radar beam sweeps the ground surface by scanning the radar beam. This method widens the observation width in the elevation direction by splitting the observation time shortened by increasing the speed of sweeping the ground surface into multiple scans in the elevation direction. However, since the time during which objects on the ground surface are irradiated with the radar beam becomes shorter, the azimuth resolution during imaging is reduced.
　これら衛星の移動と伴にレーダビームを走査する観測方式では、レーダビームの走査方法を規定するための基準点（ここでは、ビーム回転中心位置と呼称する）をはじめとする観測パラメータの設計が必要である。従来の画像レーダ及び観測パラメータ設計装置は、観測の中心時刻における衛星位置が、観測対象領域の中心に対しほぼゼロドップラー周波数（いわゆる、ゼロドップラー周波数は真横に相当する）方向にあることを前提として、観測パラメータの設定を行っていた。同前提では、地球表面上の観測対象領域や、衛星軌道上における衛星の動く範囲を直線状に近似して、同近似した観測幾何に基づき観測パラメータの設計を行っていた。図１に、スライディングスポットライト観測方式を例とする近似した観測幾何を示す。この近似した観測幾何では、衛星の観測開始位置Ｓｓ、観測終了位置Ｓｅ，ビーム回転中心位置Ｒｃが成す三角形に基づき、観測パラメータを設計する。軌道上の衛星の移動距離であるＳｓとＳｅ間の距離と、地上でのレーダビームの移動距離であるＰｂとＰｆ間の距離の比が、レーダビーム走査を行わない場合とレーダビーム走査を併用する場合のアジマス分解能の比に相当する。したがって、所望のアジマス分解能は、観測の中心時刻における衛星位置Ｓｃに対する観測対象領域の中心位置Ｐｃの距離Ｒ０と、観測対象領域の中心位置Ｐｃとビーム回転中心位置Ｒｃ間の距離Ｒ１の比により達成されるので、所望のアジマス分解能を達成する比に応じてビーム回転中心位置Ｒｃを定めていた。そして、所望のアジマス観測幅Ｘｆを達成するのに必要なビーム走査角を、同ビーム回転中心位置Ｒｃと、レーダビームの地球表面上でのアジマス方向の幅Ｘ（レーダビームのアジマスビーム幅と地表までの距離で定まる）から定めていた（例えば、非特許文献１）。 These observation methods that scan the radar beam as the satellite moves require the design of observation parameters, including a reference point (referred to here as the beam rotation center position) to specify the radar beam scanning method. It is. Conventional image radar and observation parameter design devices assume that the satellite position at the center time of observation is in the direction of approximately zero Doppler frequency (the so-called zero Doppler frequency corresponds directly to the side) with respect to the center of the observation target area. , setting observation parameters. Under this premise, the observation target area on the earth's surface and the movement range of the satellite in the satellite orbit were approximated to a straight line, and observation parameters were designed based on the approximated observation geometry. FIG. 1 shows an approximate observation geometry using a sliding spotlight observation method as an example. In this approximated observation geometry, observation parameters are designed based on a triangle formed by the observation start position S s of the satellite, the observation end position S e , and the beam rotation center position R c . The ratio of the distance between S s and S e , which is the moving distance of the satellite in orbit, and the distance between P b and P f , which is the moving distance of the radar beam on the ground, is This corresponds to the ratio of azimuth resolution when beam scanning is used together. Therefore, the desired azimuth resolution is the distance R 0 of the center position P c of the observation target area with respect to the satellite position S c at the center time of observation, and the distance between the center position P c of the observation target area and the beam rotation center position R c Since this is achieved by the ratio of R1, the beam rotation center position Rc is determined according to the ratio that achieves the desired azimuth resolution. Then, the beam scanning angle necessary to achieve the desired azimuth observation width (determined by the distance to the ground) (for example, Non-Patent Document 1).
　従来の衛星搭載画像レーダの観測パラメータ設計は、観測の中心時刻における衛星位置が、観測対象領域の中心に対しゼロドップラー周波数方向にある、又は非ゼロドップラー周波数方向にあってもその角度は数度程度であることを前提とし、地球表面上の観測対象領域を平面に、衛星軌道上における衛星の移動を直線に近似して所望の観測性能（アジマス分解能）が得られるビーム回転中心位置を定め、これを基に観測パラメータを決定する。しかしながら、実際の衛星軌道及び地球表面は楕円形状であること、あるいはその他の観測上の要求により、観測の中心時刻における衛星位置が観測対象領域の中心からの鉛直方向からずれて上記の衛星位置に関する前提が成立しなくなり（同位置関係での観測を「スクイント観測」と呼ぶ）、観測の中心時刻において衛星から観測対象領域の中心を見た斜め方向の角度（「スクイント角」と呼ぶ）が大きくなると、従来のビーム回転中心位置の決定方法では、所望の観測性能を得る観測パラメータを決定することが困難になるという問題があった。 The observation parameter design of conventional satellite-borne imaging radar is such that the satellite position at the center time of observation is in the direction of zero Doppler frequency with respect to the center of the observation target area, or even if it is in the direction of non-zero Doppler frequency, the angle is a few degrees. Assuming that the observation target area on the earth's surface is a plane, the movement of the satellite in the satellite orbit is approximated as a straight line, and the beam rotation center position where the desired observation performance (azimuth resolution) can be obtained is determined. Based on this, observation parameters are determined. However, due to the fact that the actual satellite orbit and the earth's surface are elliptical, or due to other observational requirements, the satellite position at the observation center time may deviate from the vertical direction from the center of the observation target area, and the satellite position may differ from the above satellite position. The assumption no longer holds true (observations with the same positional relationship are called "squint observations"), and the oblique angle (called "squint angle") when looking at the center of the observation target area from the satellite at the center time of observation becomes large. Therefore, with the conventional method of determining the beam rotation center position, there is a problem in that it becomes difficult to determine observation parameters that will obtain the desired observation performance.
　本開示技術は上記の課題を解決し、衛星の移動と伴にレーダビームを走査し大きなスクイント角で観測をする場合において、所望の観測性能を得られる観測パラメータを設計することが可能な観測パラメータ設計装置及び画像レーダを供することを目的とする。 The technology disclosed herein solves the above-mentioned problems, and enables observation parameters that can be designed to obtain the desired observation performance when scanning a radar beam as the satellite moves and observing at a large squint angle. The purpose is to provide design equipment and image radar.
　本開示技術に係る画像レーダは、衛星に搭載され衛星の移動と伴にレーダビーム（Ｂ）を走査する観測方式でスクイント観測を実施する画像レーダであって、観測対象領域の中心位置がレーダビーム（Ｂ）を横切る角速度に基づいて、設計仕様を満たすアジマス観測幅を達成するビーム回転中心位置を算出する衛星側パラメータ設計部（１１２）を備える。 The imaging radar according to the disclosed technology is an imaging radar that is mounted on a satellite and performs squint observation using an observation method in which the radar beam (B) is scanned as the satellite moves, and the center position of the observation target area is the radar beam (B). A satellite-side parameter design unit (112) is provided that calculates a beam rotation center position that achieves an azimuth observation width that satisfies design specifications based on the angular velocity across (B).
　本開示技術に係る画像レーダは上記構成を備えるため、衛星の移動と伴にレーダビームを走査し大きなスクイント角で観測をする場合において、所望の観測性能を得られる観測パラメータを設計することが可能である。 Since the imaging radar according to the disclosed technology has the above configuration, it is possible to design observation parameters that can obtain the desired observation performance when scanning the radar beam as the satellite moves and observing at a large squint angle. It is.
図１は、スライディングスポットライト観測方式を例とする近似した観測幾何を示す説明図である。FIG. 1 is an explanatory diagram showing approximate observation geometry using a sliding spotlight observation method as an example. 図２は実施の形態１に係るレーダシステムの構成図である。FIG. 2 is a configuration diagram of the radar system according to the first embodiment. 図３は、実施の形態１に係るレーダシステムの処理ステップを示すフローチャートである。FIG. 3 is a flowchart showing processing steps of the radar system according to the first embodiment. 図４は、スライディングスポットライト観測方式でスクイント観測を行った場合の衛星と観測対象との位置関係を示す説明図である。FIG. 4 is an explanatory diagram showing the positional relationship between a satellite and an observation target when Squint observation is performed using the sliding spotlight observation method. 図５は、観測対象領域の中心位置Ｐｃがストリップマップ観測時にレーダビーム（Ｂ）を横切る角速度（Ωｓｔｒ０）を算出する手法を示す説明図である。FIG. 5 is an explanatory diagram showing a method of calculating the angular velocity (Ω str0 ) at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation. 図６は、設計仕様を満たすアジマスビーム回転角の算出する方法を示す説明図である。FIG. 6 is an explanatory diagram showing a method for calculating an azimuth beam rotation angle that satisfies design specifications.
実施の形態１．
　図２は実施の形態１に係るレーダシステムの構成図である。図２に示されるとおり実施の形態１に係るレーダシステムは、レーダ衛星１００と、地上局２００と、から構成される。レーダ衛星１００は、衛星側パラメータ設計部１１２を含むレーダ制御部１１０を有する。地上局２００は、地上側パラメータ設計部２１２を含む観測立案部２１０を有する。
　衛星側パラメータ設計部１１２と地上側パラメータ設計部２１２とは、図２に示されるとおり異なる機能ブロックではあるが、それぞれが実施する処理の内容は同じである。本明細書では、衛星側パラメータ設計部１１２又は地上側パラメータ設計部２１２を独立した装置として呼称するときに、観測パラメータ設計装置という名称が用いられるものとする。
　レーダ衛星１００は、画像レーダであり、例えば、衛星筐体にＳＡＲセンサを搭載してなる合成開口レーダであってよい。レーダ衛星１００のＳＡＲセンサの構成要素であるレーダ制御部１１０は、地上局２００から送信された観測コマンド（Ｃ、ＣはＣｏｍｍａｎｄの頭文字を由来とする）に基づき設計した観測パラメータを用いて、地球表面にレーダビーム（Ｂ、ＢはＢｅａｍの頭文字を由来とする）を照射するようＳＡＲセンサを制御する。レーダ制御部１１０は、衛星側パラメータ設計部１１２を有し、衛星軌道（Ｏ、ＯはＯｒｂｉｔの頭文字を由来とする）上でスクイント観測向けの観測パラメータを設計する。 Embodiment 1.
FIG. 2 is a configuration diagram of the radar system according to the first embodiment. As shown in FIG. 2, the radar system according to the first embodiment includes a radar satellite 100 and a ground station 200. The radar satellite 100 has a radar control section 110 including a satellite-side parameter design section 112. The ground station 200 has an observation planning unit 210 that includes a ground-side parameter design unit 212.
Although the satellite-side parameter design unit 112 and the ground-side parameter design unit 212 are different functional blocks as shown in FIG. 2, the content of the processing that each performs is the same. In this specification, when referring to the satellite-side parameter design unit 112 or the ground-side parameter design unit 212 as an independent device, the name observation parameter design device is used.
The radar satellite 100 is an image radar, and may be, for example, a synthetic aperture radar in which a SAR sensor is mounted on a satellite housing. The radar control unit 110, which is a component of the SAR sensor of the radar satellite 100, uses observation parameters designed based on observation commands (C and C are derived from the initials of "Command") transmitted from the ground station 200. The SAR sensor is controlled to irradiate the earth's surface with a radar beam (B is derived from the initial letter "Beam"). The radar control unit 110 includes a satellite-side parameter design unit 112, which designs observation parameters for Squint observation on a satellite orbit (O is derived from the initial letter of Orbit).
　地上局２００は、レーダ衛星１００に送る観測コマンド（Ｃ）を作成する観測立案部２１０を有する。観測立案部２１０は、地上側パラメータ設計部２１２を有し、地上局２００でスクイント観測向けの観測パラメータを設計する。衛星側パラメータ設計部１１２と、地上側パラメータ設計部２１２は、スクイント観測向けの観測パラメータ設計において、いずれかが単独で観測パラメータを設計する、又は両方が連携して観測パラメータを設計する、という機能を有する。 The ground station 200 has an observation planning unit 210 that creates an observation command (C) to be sent to the radar satellite 100. The observation planning unit 210 includes a ground-side parameter design unit 212, which designs observation parameters for Squint observation at the ground station 200. The satellite-side parameter design unit 112 and the ground-side parameter design unit 212 have a function in which one of them independently designs observation parameters, or both of them work together to design observation parameters in observation parameter design for Squint observation. has.
　本開示技術に係るレーダシステムの処理ステップは、以下の図３に沿った説明により明らかとなる。図３は、実施の形態１に係るレーダシステムの処理ステップを示すフローチャートである。図３は、より具体的には、本開示技術の目的である、スクイント角が大きな観測（すなわち「スクイント観測」）を実施する場合の観測パラメータを設計する、衛星側パラメータ設計部１１２、及び地上側パラメータ設計部２１２の処理ステップを示すものである。
　図３に示すフローチャートは、本開示技術に係るレーダシステムが、スライディングスポットライト観測方式でスクイント観測を実施することを前提としたものである。 The processing steps of the radar system according to the disclosed technology will become clear from the explanation along FIG. 3 below. FIG. 3 is a flowchart showing processing steps of the radar system according to the first embodiment. More specifically, FIG. 3 shows the satellite-side parameter design unit 112 and the ground-based parameter design unit 112, which design observation parameters when performing observation with a large squint angle (i.e., “squint observation”), which is the purpose of the disclosed technology. 3 shows processing steps of the side parameter design unit 212.
The flowchart shown in FIG. 3 is based on the premise that the radar system according to the disclosed technique performs squint observation using the sliding spotlight observation method.
　図４は、スライディングスポットライト観測方式でスクイント観測を行った場合の衛星と観測対象との位置関係を示す説明図である。
　なお本開示技術は、地球形状を回転楕円体とし、衛星軌道（Ｏ）を楕円とし、３次元空間で観測幾何を取り扱うものとする。ただし見易さを考慮し、図４においては、地球形状及び衛星軌道（Ｏ）が円で表され、観測幾何が２次元平面上で表されている。 FIG. 4 is an explanatory diagram showing the positional relationship between a satellite and an observation target when Squint observation is performed using the sliding spotlight observation method.
Note that the technology disclosed herein assumes that the earth shape is a spheroid, the satellite orbit (O) is an ellipse, and the observation geometry is handled in a three-dimensional space. However, for ease of viewing, in FIG. 4, the shape of the earth and the satellite orbit (O) are represented by circles, and the observation geometry is represented on a two-dimensional plane.
　図４において、Ｓｓｑｃはスクイント観測時の観測中心時刻における衛星位置を、Ｐｃは観測対象領域の中心位置を、Ｒｓｑｃはスクイント観測時のビーム回転中心位置を、それぞれ表す。衛星は衛星軌道（Ｏ）を移動し、地球（Ｅ、ＥはＥａｒｔｈの頭文字に由来する）にレーダビーム（Ｂ）を照射する。
　参考として図４は、従来のスクイント観測ではないスライディングスポットライト観測方式の観測幾何との差異を明確にするために、従来の観測における観測中心時刻における衛星位置をＳｃで示し、従来の観測におけるビーム回転中心位置をＲｃで示す。衛星位置を意味するＳｃのＳは、衛星の英語名であるＳａｔｅｌｌｉｔｅの頭文字を由来とする。また回転中心位置を意味するＲｃのＲは、回転を英語にしたＲｏｔａｔｉｏｎの頭文字を由来とする。またのＳｃ及びＲｃの下添え字のＣは、中心を英語にしたＣｅｎｔｅｒの頭文字を由来とする。 In FIG. 4, S sqc represents the satellite position at the observation center time during Squint observation, P c represents the center position of the observation target area, and R sqc represents the beam rotation center position during Squint observation. The satellite moves in a satellite orbit (O) and irradiates a radar beam (B) to the earth (E, E is derived from the initial letter "Earth").
For reference, Figure 4 shows the satellite position at the observation center time in conventional observation as S c , in order to clarify the difference from the observation geometry of the sliding spotlight observation method, which is not the conventional Squint observation. The beam rotation center position is indicated by R c . The S in Sc , which means satellite position, is derived from the initial letter of Satellite, which is the English name for satellite. The R in Rc , which means the center of rotation, is derived from the initial letter of the English word "Rotation." The subscript C of S c and R c is derived from the initial letter of the English word Center.
　スクイント観測向けの観測パラメータ設計を地上で行う場合、ステップＳＴ３０１は、地上局２００の観測立案部２１０により実施される。ステップＳＴ３０１において観測立案部２１０は、地上側パラメータ設計部２１２へ、観測対象領域の中心位置Ｐｃと、観測中心時刻における衛星位置Ｓｓｑｃと、レーダビーム（Ｂ）のアジマスビーム幅Θａｚと、観測対象領域の所望のアジマス観測幅Ｘｆ等の設計の前提条件と、を入力する。観測立案部２１０は、入力インターフェースを介して地上局２００の操作者が上記の入力項目の入力を支援するようプログラムされていてもよい。
　スクイント観測向けの観測パラメータ設計を地上で行う場合、ステップＳＴ３０１以降の処理ステップは、地上局２００の観測立案部２１０により実施される。 When designing observation parameters for Squint observation on the ground, step ST301 is performed by the observation planning unit 210 of the ground station 200. In step ST301, the observation planning unit 210 sends to the ground-side parameter design unit 212 the center position P c of the observation target area, the satellite position S sqc at the observation center time, the azimuth beam width Θ az of the radar beam (B), Preconditions for design such as the desired azimuth observation width Xf of the observation target area are input. The observation planning unit 210 may be programmed to assist the operator of the ground station 200 in inputting the above input items via an input interface.
When designing observation parameters for Squint observation on the ground, the processing steps after step ST301 are performed by the observation planning unit 210 of the ground station 200.
　スクイント観測向けの観測パラメータ設計を衛星上で行う場合、ステップＳＴ３０１は、レーダ衛星１００のレーダ制御部１１０により実施される。ステップＳＴ３０１においてレーダ制御部１１０は、衛星側パラメータ設計部１１２へ、観測対象領域の中心位置Ｐｃと、スクイント観測時の観測中心時刻における衛星位置Ｓｓｑｃと、レーダビーム（Ｂ）のアジマスビーム幅Θａｚと、観測対象領域の所望のアジマス観測幅Ｘｆ等の設計の前提条件と、を入力する。レーダ制御部１１０は、入力インターフェースを介してレーダ衛星１００の操作者が上記の入力項目の入力を支援するようプログラムされていてもよい。
　スクイント観測時の観測中心時刻における衛星位置を意味するＳｓｑｃの下添え字のＳｑｃは、スクイントを英語にしたＳｑｕｉｎｔの最初の２文字と、中心を英語にしたＣｅｎｔｅｒの頭文字と、を由来とする。
　スクイント観測向けの観測パラメータ設計を衛星上で行う場合、ステップＳＴ３０１以降の処理ステップは、レーダ衛星１００のレーダ制御部１１０により実施される。 When designing observation parameters for Squint observation on a satellite, step ST301 is performed by the radar control unit 110 of the radar satellite 100. In step ST301, the radar control unit 110 sends to the satellite-side parameter design unit 112 the center position P c of the observation target area, the satellite position S sqc at the observation center time during Squint observation, and the azimuth beam width of the radar beam (B). Θ az and design preconditions such as the desired azimuth observation width X f of the observation target area are input. The radar control unit 110 may be programmed to assist the operator of the radar satellite 100 in inputting the above input items via an input interface.
The subscript Sqc of S sqc , which means the satellite position at the observation center time during Squint observation, is derived from the first two letters of Squint, which is the English word for Squint, and the initial letter of Center, which is the English word for Squint. do.
When designing observation parameters for Squint observation on a satellite, the processing steps after step ST301 are executed by the radar control unit 110 of the radar satellite 100.
　ステップＳＴ３０２は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０２において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、スクイント観測時の観測中心時刻から所定時間相当離れた衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと観測中心時刻から所定時間相当離れた衛星位置（前方側）Ｓｓｑｆを仮設定する。ここで、所定時間とは、例えば１０～２０［秒］の観測時間程度の時間である。
　衛星位置（後方側）を意味するＳｓｑｂの下添え字のｓｑｂは、スクイントを英語にしたＳｑｕｉｎｔの最初の２文字と、後方を英語にしたｂａｃｋの頭文字と、を由来とする。また衛星位置（前方側）を意味するＳｓｑｆの下添え字のｓｑｆは、スクイントを英語にしたＳｑｕｉｎｔの最初の２文字と、前方を英語にしたｆｏｒｗａｒｄの頭文字と、を由来とする。 Step ST302 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST302, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines the satellite position (rear side) S sqb on the satellite orbit (O) that is a predetermined time away from the observation center time during Squint observation and the observation center time. A satellite position (forward side) S sqf that is a predetermined time away from the satellite is temporarily set. Here, the predetermined time is, for example, about 10 to 20 [seconds] of observation time.
The subscript sqb of S sqb , which means the satellite position (back side), is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of back, which is the English word for backward. The subscript sqf of S sqf , which means the satellite position (forward side), is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of forward, which is the English word for Squint.
　ステップＳＴ３０３は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０３において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、観測対象領域の中心位置Ｐｃがストリップマップ観測時にレーダビーム（Ｂ）を横切る角速度Ωｓｔｒ０を算出する。 Step ST303 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST303, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the angular velocity Ω str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation.
　図５は、観測対象領域の中心位置Ｐｃがストリップマップ観測時にレーダビーム（Ｂ）を横切る角速度Ωｓｔｒ０を算出する手法を示す説明図である。
　図５に示されるＳｓｑｘは、衛星軌道（Ｏ）上における任意の衛星位置である。図５に示されるθｘは、衛星位置Ｓｓｑｘからゼロドップラー方向を基準として、衛星位置Ｓｓｑｘにおける観測対象領域の中心位置Ｐｃがなす角度である。衛星軌道（Ｏ）は観測パラメータ設計の前提条件として与えられ、衛星の速度は衛星軌道（Ｏ）の高度から物理法則に一意に定まる。したがって、同衛星位置Ｓｓｑｘでのθｘの値は、衛星位置Ｓｓｑｘの位置ベクトル、観測対象領域の中心位置Ｐｃの位置ベクトルから算出できる。
　ステップＳＴ３０３において、まず、衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆとにおける、観測対象領域の中心位置Ｐｃの角度であるθｂとθｆ（それぞれ各衛星位置でのθｘに相当する）が算出される。そして、観測対象領域の中心位置Ｐｃがストリップマップ観測時にレーダビーム（Ｂ）を横切る角速度Ωｓｔｒ０が、数式（１）で示される差分近似式で算出される。

Figure JPOXMLDOC01-appb-I000001

ここで、Ｔは、観測中心時刻から所定時間相当離れた衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと観測中心時刻から所定時間相当離れた衛星位置（前方側）Ｓｓｑｆ間の時間間隔である。 FIG. 5 is an explanatory diagram showing a method of calculating the angular velocity Ω str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation.
S sqx shown in FIG. 5 is an arbitrary satellite position on the satellite orbit (O). θ x shown in FIG. 5 is the angle formed by the center position P c of the observation target area at the satellite position S sqx with respect to the zero Doppler direction from the satellite position S sqx . The satellite orbit (O) is given as a prerequisite for designing observation parameters, and the speed of the satellite is uniquely determined by the laws of physics from the altitude of the satellite orbit (O). Therefore, the value of θ x at the satellite position S sqx can be calculated from the position vector of the satellite position S sqx and the position vector of the center position P c of the observation target area.
In step ST303, first, the angle of the center position P c of the observation target area between the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O) θ b and θ f (each corresponding to θ x at each satellite position) are calculated. Then, the angular velocity Ω str0 at which the center position P c of the observation target area crosses the radar beam (B) during strip map observation is calculated using the difference approximation formula shown in Equation (1).

Figure JPOXMLDOC01-appb-I000001

Here, T is the distance between the satellite position (back side) S sqb on the satellite orbit (O) that is a predetermined time away from the observation center time and the satellite position (front side) S sqf that is a predetermined time away from the observation center time. It is a time interval.
　ステップＳＴ３０４は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０４において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、スクイント観測時のビーム回転中心位置Ｒｓｑｃを設定するために反復計算を実施する。
　図４に示されるようにこの反復計算の処理は、スクイント観測時の観測中心時刻における衛星位置Ｓｓｑｃと観測対象領域の中心位置Ｐｃを結ぶ線分上において、所望のアジマス分解能を達成可能なＳｓｑｃとＲｓｑｃ間の距離を求めるものである。最終的にこの反復計算により、所望の観測性能を達成するビーム回転中心位置Ｒｓｑｃが求まる。 Step ST304 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST304, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 performs iterative calculation to set the beam rotation center position R sqc during Squint observation.
As shown in FIG. 4, this iterative calculation process makes it possible to achieve the desired azimuth resolution on the line segment connecting the satellite position S sqc at the observation center time during Squint observation and the center position P c of the observation target area. This is to find the distance between S sqc and R sqc . Finally, through this iterative calculation, the beam rotation center position R sqc that achieves the desired observation performance is determined.
　ステップＳＴ３０５は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０５において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、反復計算の第１のステップとして、ビーム回転中心位置Ｒｓｑｃの候補となる初期値を定める。ビーム回転中心位置Ｒｓｑｃは、スクイント観測時の観測中心時刻における衛星位置Ｓｓｑｃとビーム回転中心位置Ｒｓｑｃ間の距離を徐々に変化させながら定めるようにしてよい。
　最も原始的な反復計算の方法は、一定の間隔でもっともらしい解を探索する、というものである。反復計算処理の１回目において、ビーム回転中心位置Ｒｓｑｃの候補は、例えば、観測対象領域の中心位置Ｐｃと一致させてよい。反復計算処理の２回目以降は、ビーム回転中心位置Ｒｓｑｃの候補の更新は、例えば、観測中心時刻における衛星位置Ｓｓｑｃと観測対象領域の中心位置Ｐｃを結ぶ直線上に、観測中心時刻における衛星位置Ｓｓｑｃと観測対象領域の中心位置Ｐｃ間の距離を基準として、予め設定した増分だけ延伸した距離の位置に定めるようにしてよい。例えば、予め設定した増分を２％とすると、反復計算処理の２回目以降は、観測中心時刻における衛星位置Ｓｓｑｃからの距離が、１．０２倍、１．０４倍、１．０６倍・・・、となる位置に定められる。このように一定の間隔で計算を行うことは、傾向をつかむことの一助となる。なお、設計仕様を満たすビーム回転中心位置Ｒｓｑｃの探索は、例えば、解よりも小さい側と大きい側との両側から探索を行う二分探索法が用いられてよい。また、ビーム回転中心位置Ｒｓｑｃの計算は、目標値との誤差の二乗（本開示技術の場合、設計仕様のアジマス分解能と解候補におけるアジマス分解能との誤差の二乗）を解候補の微小変化分で数値的に偏微分し、数値的に求めた偏微分の値により探索幅を変化させるニュートン法であってもよい。 Step ST305 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST305, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines an initial value as a candidate for the beam rotation center position R sqc as a first step of the iterative calculation. The beam rotation center position R sqc may be determined by gradually changing the distance between the satellite position S sqc and the beam rotation center position R sqc at the observation center time during Squint observation.
The most primitive method of iterative calculation is to search for plausible solutions at regular intervals. In the first iteration of the iterative calculation process, the candidate for the beam rotation center position R sqc may be made to coincide with the center position P c of the observation target area, for example. From the second iterative calculation process onwards, the candidates for the beam rotation center position R sqc are updated by, for example, aligning the candidates at the observation center time on a straight line connecting the satellite position S sqc at the observation center time and the center position P c of the observation target area. The distance between the satellite position S sqc and the center position P c of the observation target area may be used as a reference, and the distance may be set at a distance extended by a preset increment. For example, if the preset increment is 2%, after the second iteration of the iterative calculation process, the distance from the satellite position S sqc at the observation center time will be 1.02 times, 1.04 times, 1.06 times, etc.・, is determined at the position. Performing calculations at regular intervals like this helps identify trends. Note that the search for the beam rotation center position R sqc that satisfies the design specifications may be performed using, for example, a binary search method in which the search is performed from both the side smaller than the solution and the side larger than the solution. In addition, to calculate the beam rotation center position R sqc , the square of the error from the target value (in the case of the disclosed technology, the square of the error between the azimuth resolution of the design specification and the azimuth resolution of the solution candidate) is calculated by calculating the minute change in the solution candidate. Newton's method may be used, in which partial differentiation is performed numerically by , and the search width is changed based on the value of the numerically determined partial differentiation.
　ステップＳＴ３０６は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０６において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、観測対象領域の中心位置Ｐｃが、現観測方式（例えば、図１に例示されるスライディングスポットライト観測方式）でレーダビーム（Ｂ）を横切る角速度Ωｓｔｒ［Ｒｓｑｃ］を算出する。
　本開示技術は、衛星軌道（Ｏ）上における任意の衛星位置Ｓｓｑｘからゼロドップラー方向を基準として、ビーム回転中心位置Ｒｓｑｃの角度をφｘと定義し、この角速度Ωｓｔｒ［Ｒｓｑｃ］の算出方法を明らかにする。衛星位置Ｓｓｑｘでのビーム回転中心位置Ｒｓｑｃの角度φｘの値は、衛星位置Ｓｓｑｘの位置ベクトル、ビーム回転中心位置Ｒｓｑｃの位置ベクトルから算出できる。 Step ST306 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST306, the ground side parameter design unit 212 or the satellite side parameter design unit 112 determines that the center position P c of the observation target area is the radar beam ( Calculate the angular velocity Ω str [R sqc ] across B).
The disclosed technology defines the angle of the beam rotation center position R sqc from an arbitrary satellite position S sqx on the satellite orbit (O) to the zero Doppler direction as φ x , and calculates the angle of this angular velocity Ω str [R sqc ]. Clarify the calculation method. The value of the angle φ x of the beam rotation center position R sqc at the satellite position S sqx can be calculated from the position vector of the satellite position S sqx and the position vector of the beam rotation center position R sqc .
　ステップＳＴ３０６において、まず、衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆとにおけるビーム回転中心位置Ｒｓｑｃの角度φｘが、それぞれφｂとφｆとして算出される。次に、算出されたφｂ及びφｆの値から、レーダビーム（Ｂ）の回転角速度ω［Ｒｓｑｃ］が数式（２）に示す差分近似式で求められる。

Figure JPOXMLDOC01-appb-I000002

　そして、現観測方式でレーダビーム（Ｂ）を横切る角速度Ωｓｔｒ［Ｒｓｑｃ］が、数式（３）で算出される。

Figure JPOXMLDOC01-appb-I000003
In step ST306, first, the angle φ , are calculated as φ b and φ f , respectively. Next, from the calculated values of φ b and φ f , the rotational angular velocity ω[R sqc ] of the radar beam (B) is determined by the difference approximation formula shown in Equation (2).

Figure JPOXMLDOC01-appb-I000002

Then, the angular velocity Ω str [R sqc ] that crosses the radar beam (B) using the current observation method is calculated using equation (3).

Figure JPOXMLDOC01-appb-I000003
　ステップＳＴ３０７は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０７において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、角速度の比（Ωｓｔｒ［Ｒｓｑｃ］／Ωｓｔｒ０）が、レーダビーム（Ｂ）のアジマスビーム幅Θａｚで定まるストリップマップ観測時のアジマス分解能δａｚ０と設計の前提条件として与えられる所望のアジマス分解能δａｚの比δａｚ／δａｚ０と同等かどうかを判定する。
　ステップＳＴ３０７において、ストリップマップ観測時のアジマス分解能δａｚ０は、例えば、以下の数式（４）で与えられる。

Figure JPOXMLDOC01-appb-I000004

ただし、λはレーダで用いられるレーダ波の波長である。 Step ST307 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST307, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 performs strip map observation in which the angular velocity ratio (Ω str [R sqc ]/Ω str0 ) is determined by the azimuth beam width Θ az of the radar beam (B). It is determined whether the ratio δ az /δ az0 of the azimuth resolution δ az0 at the time and the desired azimuth resolution δ az given as a precondition for design is equal.
In step ST307, the azimuth resolution δ az0 at the time of strip map observation is given by, for example, the following equation (4).

Figure JPOXMLDOC01-appb-I000004

However, λ is the wavelength of radar waves used in radar.
　ステップＳＴ３０７において実施される判定は、以下に示す原理を根拠としている。合成開口レーダのアジマス分解能は合成開口角で決まる、という事実がある。ストリップマップ観測時は、合成開口角はアジマスビーム幅と等価である。そこで、衛星の移動に伴いレーダビーム（Ｂ）を走査するスポットライトやスライディングスポットライト観測においては、レーダビーム（Ｂ）を走査することで合成開口角を大きくしてアジマス分解能を向上させることが行われる。本開示技術では、このビーム走査による合成開口角の変化が、レーダビーム（Ｂ）の角速度の変化に帰着できることに着目する。つまり、ストリップマップ観測時の角速度Ωｓｔｒ０に比べ、レーダビーム（Ｂ）の走査により角速度Ωｓｔｒ［Ｒｓｑｃ］を遅くすることが、点目標にレーダビーム（Ｂ）が照射されている時間を長くし合成開口角を大きくすることに相当する。すなわち、ストリップマップ観測時の角速度Ωｓｔｒ０を基準としたレーダビーム（Ｂ）の角速度の比が、アジマス分解能の向上比に相当する。そこで、ステップＳＴ３０７においては、角速度の比を用いることにより、所望のアジマス分解能が得られたか否かを判断する、ということを行う。
　ステップＳＴ３０７において角速度の比が同じだと判定された場合は、反復計算の処理が完了する。角速度の比を同じでないと判定された場合は、処理工程がステップＳＴ３０５に戻り、反復計算の処理が継続する。 The determination performed in step ST307 is based on the principle shown below. It is a fact that the azimuth resolution of synthetic aperture radar is determined by the synthetic aperture angle. During strip map observation, the synthetic aperture angle is equivalent to the azimuth beam width. Therefore, in spotlight and sliding spotlight observations that scan the radar beam (B) as the satellite moves, it is possible to increase the synthetic aperture angle and improve the azimuth resolution by scanning the radar beam (B). be exposed. The disclosed technique focuses on the fact that a change in the synthetic aperture angle due to this beam scanning can result in a change in the angular velocity of the radar beam (B). In other words, compared to the angular velocity Ω str0 during strip map observation, slowing down the angular velocity Ω str [R sqc ] by scanning the radar beam (B) increases the time that the point target is irradiated with the radar beam (B). This corresponds to increasing the synthetic aperture angle. That is, the ratio of the angular velocity of the radar beam (B) with respect to the angular velocity Ω str0 at the time of strip map observation corresponds to the improvement ratio of the azimuth resolution. Therefore, in step ST307, it is determined by using the ratio of angular velocities whether or not the desired azimuth resolution has been obtained.
If it is determined in step ST307 that the angular velocity ratios are the same, the iterative calculation process is completed. If it is determined that the angular velocity ratios are not the same, the process returns to step ST305 and the iterative calculation process continues.
　ステップＳＴ３０８は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０８において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、反復計算の処理において最終的に得られたビーム回転中心位置Ｒｓｑｃを、所望のビーム回転中心位置である、すなわち設計仕様を満たすビーム回転中心位置である、と決定する。 Step ST308 is a processing step performed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST308, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 determines that the beam rotation center position R sqc finally obtained in the iterative calculation process is the desired beam rotation center position, that is, the design specification. The beam rotation center position that satisfies the
　ステップＳＴ３０９は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３０９において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、設計仕様を満たすアジマスビーム回転角の算出を行う。ステップＳＴ３０９で算出されるアジマスビーム回転角は、所望のアジマス観測幅を実現する、すなわち設計仕様を満たすアジマス分解能を実現する、ビーム回転中心位置Ｒｓｑｃ、におけるものである。 Step ST309 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST309, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates an azimuth beam rotation angle that satisfies the design specifications. The azimuth beam rotation angle calculated in step ST309 is at the beam rotation center position R sqc that achieves the desired azimuth observation width, that is, the azimuth resolution that satisfies the design specifications.
　図６は、ステップＳＴ３０９において設計仕様を満たすアジマスビーム回転角の算出する方法を示す説明図である。
　図６において、Ｐｂは観測対象領域のアジマス観測端（後方）を、Ｐｆは観測対象領域のアジマス観測端（前方）を、それぞれ表す。また図６において、Ｓｓｑｓは観測開始時の衛星位置を、Ｓｓｑｅは観測終了時の衛星位置を、それぞれ表す。観測開始時の衛星位置を意味するＳｓｑｓの下添え字のＳｑｓは、スクイントを英語にしたＳｑｕｉｎｔの最初の２文字と、開始を英語にしたｓｔａｒｔの頭文字と、を由来とする。観測終了時の衛星位置を意味するＳｓｑｅの下添え字のＳｑｅは、スクイントを英語にしたＳｑｕｉｎｔの最初の２文字と、終了を英語にしたｅｎｄの頭文字と、を由来とする。さらに図６において、θｓｑｃは観測中心時刻における衛星位置Ｓｓｑｃにおけるビーム走査角を、θｓｑｓは衛星位置Ｓｓｑｓにおけるビーム走査角を、θｓｑｅは衛星位置Ｓｓｑｅにおけるビーム走査角を、それぞれ表す。
　ビーム走査角のθｓｑｃ、θｓｑｓ、及びθｓｑｅは、それぞれの衛星位置からビーム回転中心位置Ｒｓｑｃへのベクトルと、ゼロドップラー方向へのベクトルと、が成す角として定義される。
　また、φＲは、衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆに対するビーム回転中心でのアジマスビーム回転角である。 FIG. 6 is an explanatory diagram showing a method of calculating an azimuth beam rotation angle that satisfies the design specifications in step ST309.
In FIG. 6, P b represents the azimuth observation end (backward) of the observation target area, and P f represents the azimuth observation end (front) of the observation target area. Further, in FIG. 6, S sqs represents the satellite position at the start of observation, and S sqe represents the satellite position at the end of observation. The subscript Sqs of S sqs , which means the satellite position at the start of observation, is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of start, which is the English word for Squint. The subscript Sqe of S sqe , which means the satellite position at the end of observation, is derived from the first two letters of Squint, which is the English word for Squint, and the first letter of end, which is the English word for End. Further, in FIG. 6, θ sqc represents the beam scanning angle at the satellite position S sqc at the observation center time, θ sqs represents the beam scanning angle at the satellite position S sqs , and θ sqe represents the beam scanning angle at the satellite position S sqe . .
The beam scanning angles θ sqc , θ sqs , and θ sqe are defined as angles formed by a vector from each satellite position to the beam rotation center position R sqc and a vector in the zero Doppler direction.
Further, φ R is the azimuth beam rotation angle at the beam rotation center with respect to the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O).
　図６中のいわゆる漫画の吹き出しに示された部分は、ビーム回転中心位置Ｒｓｑｃと、地球表面上の点Ｐｂ、Ｐｃ、Ｐｆとの幾何関係を、拡大して示したものである。
　図６において、ｌｂ、ｌｃ、ｌｆは、ビーム回転中心位置Ｒｓｑｃと点Ｐｂ、Ｐｃ、Ｐｆとのそれぞれを結ぶ線分の距離を表す。ψｂとψｆとは、それぞれＰｂ－Ｒｓｑｃ－Ｐｃ、Ｐｃ－Ｒｓｑｃ－Ｐｆが成す角度を表す。 The part shown in the so-called comic balloon in FIG. 6 is an enlarged view of the geometric relationship between the beam rotation center position R sqc and the points P b , P c , and P f on the earth's surface. .
In FIG. 6, l b , l c , and l f represent distances between line segments connecting the beam rotation center position R sqc and points P b , P c , and P f , respectively. ψ b and ψ f represent angles formed by P b -R sqc -P c and P c -R sqc -P f , respectively.
　観測対象領域の両端である点ＰｂとＰｆ間の距離Ｌｂｆは、以下の数式（５）で与えられる。

Figure JPOXMLDOC01-appb-I000005

ここで、Ｘｆは観測対象領域の所望のアジマス観測幅、Θａｚはレーダビーム（Ｂ）のアジマスビーム幅、Ｒｃｓｑは観測中心時刻における衛星位置Ｓｓｑｃと観測対象領域の中心位置Ｐｃ間の距離である。 The distance L bf between points P b and P f , which are both ends of the observation target area, is given by the following equation (5).

Figure JPOXMLDOC01-appb-I000005

Here, X f is the desired azimuth observation width of the observation target area, Θ az is the azimuth beam width of the radar beam (B), and R csq is the distance between the satellite position S sqc and the center position P c of the observation target area at the observation center time. is the distance.
　点Ｐｆ－Ｐｃ－Ｒｓｑｃが成す角度φｓｑｃは、以下の数式（６）で与えられる。

Figure JPOXMLDOC01-appb-I000006

ここで、数式（５）で求めたＬｂｆの半分の距離は、記号のＬｈａ（Ｌｈａ＝Ｌｂｆ／２）により表されるものとする。 The angle φ sqc formed by the points P f -P c -R sqc is given by the following equation (6).

Figure JPOXMLDOC01-appb-I000006

Here, it is assumed that the half distance of L bf calculated using formula (5) is represented by the symbol L ha (L ha =L bf /2).
　ステップＳＴ３０９において、線分長ｌｃは、それぞれ既に求められている観測対象領域の中心位置Ｐｃとビーム回転中心位置Ｒｓｑｃとのそれぞれの位置ベクトルから、算出される。また線分長ｌｂ及びｌｆは、Ｌｈａと角度φｓｑｃから、余弦定理を用いて算出される。
　ステップＳＴ３０９において、ビーム回転中心位置Ｒｓｑｃでのアジマスビーム回転角角度ψｂは、線分長ｌｂとＬｈａ及び角度φｓｑｃから、正弦定理を用いて算出される。ビーム回転中心位置Ｒｓｑｃでのアジマスビーム回転角角度ψｆは、ｌｆとＬｈａ及び角度φｓｑｃから、同様に正弦定理を用いて算出される。 In step ST309, the line segment length l c is calculated from the respective position vectors of the center position P c of the observation target area and the beam rotation center position R sqc , which have already been determined. Further, the line segment lengths l b and l f are calculated from L ha and the angle φ sqc using the cosine theorem.
In step ST309, the azimuth beam rotation angle ψ b at the beam rotation center position R sqc is calculated from the line segment lengths l b and L ha and the angle φ sqc using the law of sine. The azimuth beam rotation angle ψ f at the beam rotation center position R sqc is similarly calculated from l f , L ha , and the angle φ sqc using the law of sine.
　ステップＳＴ３１０は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３１０において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、ビーム回転中心位置Ｒｓｑｃにおけるアジマスビーム回転角と、衛星軌道（Ｏ）上でのアジマスビーム回転角と、の比を算出する。
　ステップＳＴ３１０において衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆに対する、ビーム回転中心位置Ｒｓｑｃでのアジマスビーム回転角φＲは、以下の数式（７）に基づいて算出される。

Figure JPOXMLDOC01-appb-I000007

ここで、Ｒｓｑｃはビーム回転中心位置Ｒｓｑｃの位置ベクトルを、Ｓｓｑｂは衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂの位置ベクトルを、Ｓｓｑｆは衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆの位置ベクトルを、それぞれ表す。数式（７）の右辺における記号の・は、ベクトルの内積を表す演算子である。また数式（７）の右辺における絶対値の記号は、ベクトルの大きさを表すものである。 Step ST310 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST310, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the ratio between the azimuth beam rotation angle at the beam rotation center position R sqc and the azimuth beam rotation angle on the satellite orbit (O). .
In step ST310, the azimuth beam rotation angle φ R at the beam rotation center position R sqc with respect to the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O) is calculated based on the following formula (7).

Figure JPOXMLDOC01-appb-I000007

Here, R sqc is the position vector of the beam rotation center position R sqc , S sqb is the position vector of the satellite position (rear side) S sqb on the satellite orbit (O), and S sqf is the position vector of the satellite position (rear side) on the satellite orbit (O). The position vector of the satellite position (front side) S sqf is represented respectively. The symbol . on the right side of Equation (7) is an operator representing the inner product of vectors. Further, the symbol for the absolute value on the right side of Equation (7) represents the magnitude of the vector.
　ステップＳＴ３１０において、衛星軌道（Ｏ）上の衛星位置（後方側）Ｓｓｑｂと、衛星軌道（Ｏ）上の衛星位置（前方側）Ｓｓｑｆと、から、衛星軌道（Ｏ）上でのアジマスビーム回転角θＲは、以下の数式（８）に基づいて算出される。

Figure JPOXMLDOC01-appb-I000008
In step ST310, an azimuth beam on the satellite orbit (O) is determined from the satellite position (rear side) S sqb on the satellite orbit (O) and the satellite position (front side) S sqf on the satellite orbit (O). The rotation angle θ R is calculated based on the following formula (8).

Figure JPOXMLDOC01-appb-I000008
　ステップＳＴ３１０において、衛星軌道（Ｏ）上とビーム回転中心位置におけるアジマスビーム角度の比ａｎｇｒは、以下の数式（９）に基づいて算出される。

Figure JPOXMLDOC01-appb-I000009
In step ST310, the ratio angr of the azimuth beam angle on the satellite orbit (O) and at the beam rotation center position is calculated based on the following equation (9).

Figure JPOXMLDOC01-appb-I000009
　ステップＳＴ３１１は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３１１において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、所望のアジマス観測幅の達成に必要な観測時間Ｔｏｂｓを、すなわち設計仕様を満たす観測時間Ｔｏｂｓを、以下の数式（１０）に基づいて算出する。

Figure JPOXMLDOC01-appb-I000010

ここで、関数ＭＡＸ［］は、入力引数の内の最大値を返す関数である。また、ｍは時間マージンを付与するための係数である。 Step ST311 is a processing step performed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST311, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 calculates the observation time T obs required to achieve the desired azimuth observation width, that is, the observation time T obs that satisfies the design specifications, using the following formula (10 ) Calculated based on

Figure JPOXMLDOC01-appb-I000010

Here, the function MAX[] is a function that returns the maximum value among input arguments. Further, m is a coefficient for providing a time margin.
　ステップＳＴ３１２は、地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２が実施する処理ステップである。ステップＳＴ３１２において地上側パラメータ設計部２１２又は衛星側パラメータ設計部１１２は、ステップＳＴ３１１にて算出した観測時間Ｔｏｂｓと、スクイント観測時の観測中心時刻における衛星位置Ｓｓｑｃと、に基づいて、観測開始時の衛星位置Ｓｓｑｓ及び観測終了時の衛星位置Ｓｓｑｆを求める。
　さらにステップＳＴ３１２において、それぞれの衛星位置の位置ベクトルとビーム回転中心位置Ｒｓｑｃの位置ベクトルに基づいて、衛星位置Ｓｓｑｓにおけるビーム走査角θｓｑｓと、衛星位置Ｓｓｑｅにおけるビーム走査角θｓｑｅと、が求められる。 Step ST312 is a processing step executed by the ground-side parameter design unit 212 or the satellite-side parameter design unit 112. In step ST312, the ground-side parameter design unit 212 or the satellite-side parameter design unit 112 starts observation based on the observation time T obs calculated in step ST311 and the satellite position S sqc at the observation center time during Squint observation. The satellite position S sqs at the time of observation and the satellite position S sqf at the end of observation are determined.
Furthermore, in step ST312, based on the position vector of each satellite position and the position vector of the beam rotation center position R sqc , a beam scanning angle θ sqs at the satellite position S sqs , a beam scanning angle θ sqe at the satellite position S sqe , is required.
　ステップＳＴ３１３は、レーダ制御部１１０が実施する処理ステップである。ステップＳＴ３１３においてレーダ制御部１１０は、ステップＳＴ３０１からステップＳＴ３１２までの処理に算出した観測パラメータに基づいて、レーダ衛星１００を制御し観測を実施する。 Step ST313 is a processing step performed by the radar control unit 110. In step ST313, radar control section 110 controls radar satellite 100 to perform observation based on the observation parameters calculated in the processing from step ST301 to step ST312.
　以上のように本開示技術は、観測パラメータ設計を、衛星軌道（Ｏ）及び地球（Ｅ）の形状を直線状に近似した観測幾何で行わずに、衛星軌道（Ｏ）及び地球（Ｅ）の形状を考慮した観測幾何で行うものである。本開示技術は、衛星軌道（Ｏ）及び地球（Ｅ）の形状を直線と近似できないスクイント観測においても、衛星の移動と伴にレーダビーム（Ｂ）を走査する観測方式での観測パラメータ設計が可能となり、同観測を実現できる。 As described above, the disclosed technology does not design observation parameters using observation geometry that approximates the shapes of the satellite orbit (O) and the earth (E) to a straight line. This is done using observational geometry that takes shape into consideration. The disclosed technology enables observation parameter design using an observation method that scans the radar beam (B) as the satellite moves, even in Squint observation where the shape of the satellite orbit (O) and the earth (E) cannot be approximated to a straight line. Therefore, the same observation can be realized.
　本開示技術は、観測パラメータ設計を、衛星の移動と伴にレーダビーム（Ｂ）を走査する観測方式での観測対象領域の中心位置がレーダビーム（Ｂ）を横切る角速度に基づいて行うことにより、衛星軌道（Ｏ）及び地球（Ｅ）の形状について考慮することができる。 The technology disclosed herein designs observation parameters based on the angular velocity at which the center position of the observation target area crosses the radar beam (B) in an observation method in which the radar beam (B) scans as the satellite moves. The satellite orbit (O) and the shape of the earth (E) can be considered.
　ビーム回転中心位置の設計は、例えば、反復計算の処理を用いて行うことができる。本開示技術は、スクイント観測においても、所望のアジマス分解能を実現できるビーム回転中心位置を高精度に算出することができる。 The beam rotation center position can be designed using, for example, iterative calculation processing. The disclosed technology can calculate with high precision the beam rotation center position that can achieve a desired azimuth resolution even in squint observation.
　本開示技術は、ビーム回転中心位置と衛星軌道（Ｏ）上でのレーダビーム（Ｂ）の回転角度の比を考慮しているので、スクイント観測においても、所望のアジマス観測幅を達成するのに必要な観測時間を高精度に算出することができる。 Since the disclosed technology takes into account the ratio of the beam rotation center position and the rotation angle of the radar beam (B) on the satellite orbit (O), it is possible to achieve the desired azimuth observation width even in Squint observation. The required observation time can be calculated with high precision.
　本開示技術は、所望のアジマス観測幅の達成に必要なビーム回転中心位置の回転角を、すなわち設計仕様を満たすビーム回転中心位置の回転角を、余弦定理及び正弦定理に基づいて算出できることを明らかにした。本開示技術によれば、所望のアジマス観測幅の達成に必要な観測時間を、低い計算負荷で算出することができる。 It is clear that the disclosed technology can calculate the rotation angle of the beam rotation center position necessary to achieve a desired azimuth observation width, that is, the rotation angle of the beam rotation center position that satisfies the design specifications, based on the law of cosines and the law of sine. I made it. According to the disclosed technique, the observation time required to achieve a desired azimuth observation width can be calculated with a low calculation load.
　本開示技術は、例えば、衛星筐体にＳＡＲセンサを搭載してなる合成開口レーダ等の画像レーダに適用できるため、産業上の利用可能性を有する。 The disclosed technology has industrial applicability because it can be applied, for example, to an image radar such as a synthetic aperture radar in which a SAR sensor is mounted on a satellite housing.
　１００　レーダ衛星、１１０　レーダ制御部、１１２　衛星側パラメータ設計部、２００　地上局、２１０　観測立案部、２１２　地上側パラメータ設計部。 100 Radar satellite, 110 Radar control unit, 112 Satellite side parameter design unit, 200 Ground station, 210 Observation planning unit, 212 Ground side parameter design unit.

Claims (6)

  1. 　衛星に搭載され前記衛星の移動と伴にレーダビームを走査する観測方式でスクイント観測を実施する画像レーダであって、
    　観測対象領域の中心位置が前記レーダビームを横切る角速度に基づいて、設計仕様を満たすアジマス観測幅を達成するビーム回転中心位置を算出する衛星側パラメータ設計部を備える、
    画像レーダ。     An imaging radar that is mounted on a satellite and performs squint observation using an observation method that scans a radar beam as the satellite moves,
    a satellite-side parameter design unit that calculates a beam rotation center position that achieves an azimuth observation width that satisfies design specifications, based on the angular velocity at which the center position of the observation target area crosses the radar beam;
    Image radar.
  2. 　衛星に搭載され前記衛星の移動と伴にレーダビームを走査する観測方式でスクイント観測を実施する画像レーダの観測パラメータ設計装置であって、
    　観測対象領域の中心位置が前記レーダビームを横切る角速度に基づいて、設計仕様を満たすアジマス観測幅を達成するビーム回転中心位置を算出する、
    観測パラメータ設計装置。     An observation parameter design device for an imaging radar that is mounted on a satellite and performs squint observation using an observation method that scans a radar beam as the satellite moves,
    calculating a beam rotation center position that achieves an azimuth observation width that satisfies design specifications, based on the angular velocity at which the center position of the observation target area crosses the radar beam;
    Observation parameter design device.
  3. 　衛星に搭載され前記衛星の移動と伴にレーダビームを走査する観測方式でスクイント観測を実施する画像レーダと、
    　前記画像レーダへ観測コマンドを送信する地上局と、
    　から構成されるレーダシステムであって、
    　前記地上局は、
    　観測対象領域の中心位置が前記レーダビームを横切る角速度に基づいて、設計仕様を満たすアジマス観測幅を達成するビーム回転中心位置を算出する地上側パラメータ設計部を備える、
    レーダシステム。     an imaging radar that is mounted on a satellite and performs squint observation using an observation method that scans a radar beam as the satellite moves;
    a ground station that transmits observation commands to the image radar;
    A radar system consisting of
    The ground station is
    a ground-side parameter design unit that calculates a beam rotation center position that achieves an azimuthal observation width that satisfies design specifications, based on the angular velocity at which the center position of the observation target area crosses the radar beam;
    radar system.
  4. 　前記衛星側パラメータ設計部は、
    　前記ビーム回転中心位置と衛星軌道上での前記レーダビームの回転角度の比に基づいて設計仕様を満たすアジマス観測幅を達成する観測時間を設計する、
    請求項１に記載の画像レーダ。     The satellite-side parameter design unit includes:
    designing an observation time to achieve an azimuth observation width that satisfies design specifications based on a ratio of the beam rotation center position and the rotation angle of the radar beam on the satellite orbit;
    The image radar according to claim 1.
  5. 　前記ビーム回転中心位置と衛星軌道上での前記レーダビームの回転角度の比に基づいて設計仕様を満たすアジマス観測幅を達成する観測時間を設計する、
    請求項２に記載の観測パラメータ設計装置。     designing an observation time to achieve an azimuth observation width that satisfies design specifications based on a ratio of the beam rotation center position and the rotation angle of the radar beam on the satellite orbit;
    The observation parameter design device according to claim 2.
  6. 　前記地上側パラメータ設計部は、
    　前記ビーム回転中心位置と衛星軌道上での前記レーダビームの回転角度の比に基づいて設計仕様を満たすアジマス観測幅を達成する観測時間を設計する、
    請求項３に記載のレーダシステム。     The ground side parameter design department
    designing an observation time to achieve an azimuth observation width that satisfies design specifications based on a ratio of the beam rotation center position and the rotation angle of the radar beam on the satellite orbit;
    The radar system according to claim 3.
PCT/JP2022/018648 2022-04-25 2022-04-25 Image radar, observation parameter designing device, and radar system WO2023209751A1 (en)

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