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CN-116859390-B - FrFT-based three-dimensional positioning method for SAR (synthetic Aperture Radar) target on satellite-borne curve track

CN116859390BCN 116859390 BCN116859390 BCN 116859390BCN-116859390-B

Abstract

The invention provides a space-borne curve track SAR target three-dimensional positioning method based on FrFT. And then, carrying out fractional Fourier transform (FrFT) on the azimuth signal where the target is positioned to estimate the Doppler frequency and the initial frequency. And finally calculating the three-dimensional coordinates of the target through the estimated parameters. The invention combines the FrFT, and compared with the traditional method, the invention can effectively improve the estimation speed and reduce the signal-to-noise ratio loss.

Inventors

  • CHEN ZHIYANG
  • Nie Zhitong
  • LI YUANHAO
  • HU CHENG

Assignees

  • 北京理工大学
  • 北京理工大学前沿技术研究院

Dates

Publication Date
20260512
Application Date
20230823

Claims (6)

  1. 1. The method for three-dimensionally positioning the target of the space-borne curve track SAR based on the FrFT is characterized by comprising the following steps of: s1, acquiring space parameters of a satellite, including the motion trail of the satellite and the speed of the satellite under a fixed coordinate system of the earth center at the center moment of the synthetic aperture Acquiring load parameters of the satellite including wavelength Bandwidth of Time of synthetic aperture Pulse repetition frequency PRF; S2, imaging an observation target, wherein the specific steps include: S21, taking the beam center position as a scene center point Taking the connecting line of the ground center and the scene center point as a connecting line The axis and the satellite speed direction are The axial and ground distance is Constructing a scene coordinate system by an axis; s22, constructing a two-dimensional frequency spectrum of a reference point; s23, the frequency spectrum of the echo signal is converted into a reference two-dimensional frequency spectrum Conjugate multiplication and then inverse Fourier transformation are carried out to obtain imaging results, wherein In order to be distance-wise frequency, Is the azimuth frequency; S3, estimating Doppler tone frequency and initial frequency of a target, wherein the method comprises the following specific steps: s31, searching the position of a target according to the SAR image after imaging, and then taking out signals in the azimuth direction of the target to perform fast Fourier transform; S32, carrying out dimension normalization on the frequency domain signal after FFT, and introducing a scale factor To the original signal time domain Frequency domain Conversion to dimensionless domains Obtaining new scale coordinates; s33, performing different orders on the signals subjected to the scale conversion FrFT transformation of (2) to form The two-dimensional energy distribution diagram of the plane is then searched for the position of the energy peak point, and the initial frequency of the signal is calculated according to the peak position And frequency modulation rate ; S4, calculating the three-dimensional coordinates of the target, wherein the method specifically comprises the following steps: S41, calculating target azimuth coordinates; s42, calculating the Doppler frequency difference between O, B points, The point is a scene center point, and the point B is a target point; S43, calculating the Doppler frequency difference between A, B points, wherein A is a ground reference point and B is a target point; s44, calculating the height coordinate of the target point; s45, finally calculating the ground distance coordinate of the target B.
  2. 2. The method for three-dimensional positioning of a target of a space-borne curved-path SAR based on FrFT as set forth in claim 1, wherein in step S21, the beam center position is taken as a scene center point Taking the connecting line of the ground center and the scene center point as a connecting line The axis and the satellite speed direction are The axial and ground distance is Axis-building scene coordinate system, diagonal history of scene center points Performing polynomial fitting ; Wherein the method comprises the steps of In order to be a slow time period, Is a polynomial The order coefficient is used to determine the degree of the coefficient, Is the 0 th order term.
  3. 3. The method for three-dimensional positioning of a target of a space-borne curve-locus SAR based on FrFT as set forth in claim 1, wherein in step S22, the two-dimensional spectrum of the constructed reference point is ; Wherein the method comprises the steps of In order to adjust the frequency in the distance direction, In order to achieve the light velocity, the light beam is, As the carrier frequency of the signal, In order to be distance-wise frequency, Is the azimuthal frequency.
  4. 4. The method for three-dimensional positioning of a target of a space-borne curved-track SAR based on FrFT as set forth in claim 1, wherein in step S22, a frequency domain imaging method is employed, and the frequency spectrum is spread to Is a sixth order of (2).
  5. 5. The method for three-dimensional positioning of a target of a FrFT-based space-borne curved-line SAR according to claim 1, wherein in step S44, the height coordinates of the target point are calculated by: ; Wherein, the As a function of the wavelength(s), For the tilt of the satellite to the ground reference point a at the aperture centre moment, For the radius of the earth, For the satellite orbit to be at a height from the ground, The included angle between the earth center-satellite and the earth center-ground reference point A is the satellite motion speed v.
  6. 6. The method for three-dimensional positioning of a target of a FrFT-based space-borne curved-line SAR according to claim 1, wherein in step S45, the ground range coordinates of the target B are calculated by: ; Wherein, the Is the y-coordinate of the satellite at the center of the synthetic aperture, For the z-coordinate of the satellite at the center of the synthetic aperture, For the satellite to ground reference point B skew at the aperture center moment, Is the x-directional coordinate of the target point, Is the height direction coordinate of the target point.

Description

FrFT-based three-dimensional positioning method for SAR (synthetic Aperture Radar) target on satellite-borne curve track Technical Field The invention belongs to the technical field of synthetic aperture radars, and particularly relates to a three-dimensional positioning method for a satellite-borne curve track SAR target based on fractional Fourier transform (FrFT). Background The synthetic aperture radar has all-day and all-weather observation capability and higher resolution, and is important in earth observation at present. The conventional SAR two-dimensional image only can present the approximate position of the target, has the problems of overlapping and masking, inverted top and bottom and the like, and cannot reflect the height information of the target. Especially in urban areas with high-rise forestation and complex structures, the phenomenon of overlap and covering is obvious, and the cities are the necessary places for modern war, and the strategic positions are self-evident. Due to the problems, the SAR three-dimensional imaging technology becomes a research hot spot at home and abroad in recent years. Currently, common techniques in SAR three-dimensional imaging include tomosynthesis SAR, array interferometry SAR, and circular SAR. The SAR technology is also called as multi-baseline SAR technology, and the radar observation platform repeatedly flies at different heights, so that a synthetic aperture is formed in the height direction, and high resolution in a distance-height two-dimensional plane is realized. The array interference SAR technology is to carry a plurality of antennas on an observation platform, acquire a multichannel SAR image through a multi-input multi-output technology, and can realize single-navigation three-dimensional imaging. The circular SAR technology refers to that an observation platform performs circular motion around a target to acquire the omnidirectional information of the target. The synthetic aperture can be formed on the distance-azimuth two-dimensional plane and the distance-elevation two-dimensional plane to realize high resolution by only one flight, so that the problem of time consumption of the chromatographic SAR is solved. However, the above-mentioned existing SAR three-dimensional imaging methods all need to be based on a large amount of data, and the time required for collecting the data is long and the processing procedure is complicated. The curve track SAR can realize single navigation target reconstruction by only needing part of the track of the curve track SAR, the required data volume is small, and the data acquisition time is saved. However, the existing curve track SAR imaging method is based on a sub-aperture dividing mode to extract Doppler frequency residual errors of the target, so that not only is the signal to noise ratio lost, but also the processing speed is slower. Therefore, a method of rapidly estimating the three-dimensional position of the object is urgently needed. Disclosure of Invention In order to solve the problems, the invention provides a three-dimensional positioning method of a satellite-borne curve track SAR target based on fractional Fourier transform (FrFT), which can quickly estimate Doppler frequency modulation residual error and target initial frequency of the target through the FrFT, and can quickly complete three-dimensional positioning of the target by combining the relation between the Doppler frequency modulation residual error and the target height and the relation between the target initial frequency and azimuth position. The method for three-dimensionally positioning the target of the space-borne curve track SAR based on the FrFT comprises the following steps: s1, acquiring space parameters of a satellite, wherein the space parameters comprise a motion track of the satellite, a velocity v of the synthetic aperture at the moment of the center of the Earth Center (ECF) coordinate system and a beam center position. The loading parameters of the satellite are acquired, including wavelength lambda, bandwidth B, synthetic aperture time T s, pulse repetition frequency PRF. S2, imaging an observation target, wherein the specific steps include: S21, taking the beam center position as a scene center point O, taking the connecting line of the earth center and the scene center point as a z axis, taking the satellite speed direction as an x axis and taking the earth distance direction as a y axis to construct a scene coordinate system. Polynomial fitting of the slope distance history R (eta) of the scene center point R(η)=R0+k1η+k2η2+k3η3+k4η4 (1) Where η is the slow time, k 1-k4 is the polynomial 1-4 coefficients and R 0 is the 0 term. S22, constructing a two-dimensional frequency spectrum of a reference point as Wherein K r is distance direction frequency, c is light speed, f c is carrier frequency, f r is distance direction frequency, and f a is azimuth direction frequency. S23, performing conjugate multiplication on