Single-station moving ship active and passive cooperative positioning method based on relaxation transformation

Abstract

The invention provides a single-station moving ship active and passive cooperative positioning method based on relaxation transformation. The method comprises the following steps that a single-station synthetic aperture radar receives multiple frames of radiation pulse signals from a ship, the pulse repetition interval sum, the time difference of arrival measurement value and the Doppler phase measurement value of the ship are obtained, and then a passive measurement matrix of the ship is determined; based on the sum of pulse repetition intervals and the speed and the position of the ship, determining a theoretical measurement matrix of the ship so as to construct a ship positioning model, and solving by using a weighted least square method and a positive semidefinite relaxation transformation algorithm to obtain the predicted position and the predicted speed of the ship; transmitting radar waves to the predicted position of the ship to obtain scene echoes of the ship; designing a matched filter to perform coarse focusing on the scene echo and extract a peak signal, and performing inverse focusing inversion on the peak signal to obtain an echo signal of the ship; the ship is imaged through the echo signals, and the actual position of the ship is determined according to the imaging result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar detection and target positioning, and in particular to a single-station moving ship active and passive cooperative positioning method based on relaxation transformation. BACKGROUND

[0002] At present, the traditional active detection technology such as the single-station synthetic aperture radar (SAR) on the satellite processes the two-dimensional high-resolution image containing the distance and azimuth of the static target in the observed scene, but the single-station SAR will have an azimuth deviation problem when imaging the moving target such as a ship, resulting in the distortion of the position information of the ship. At the same time, the radiation source signal emitted by the ship-borne radar at the same wave band and received by the SAR will cause interference to the SAR, so that the position information of the ship in the SAR image is lost.

[0003] At present, there are mainly two types of methods for single-station SAR to realize the repositioning of a ship: the first type is the Doppler center frequency estimation method, and the second type is the ship wake method. The Doppler center frequency estimation method estimates the Doppler intermediate frequency of the ship and its adjacent sea surface particles in the SAR image, and estimates the radial velocity of the ship based on the Doppler intermediate frequency difference between the ship and the SAR, so as to realize the repositioning. The ship wake method uses the representation of the wake generated by the ship movement in the SAR image to realize the repositioning of the ship.

[0004] The passive detection technology is not affected by whether the ship is moving or not, and realizes the positioning of the moving ship through the algebraic relationship between the received ship-borne radiation source signal or its parameters and the position and speed of the ship. At present, the passive positioning method for the moving ship mainly realizes the positioning by constructing an optimization model through the Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) of the received radiation pulse signals of the target ship. The single-station moving ship passive positioning method has the problem that the state of the radiation source corresponding to the received signal parameters changes with time, resulting in great difficulty in inverting the motion parameters of the radiation source. The above passive detection methods all assume that the receiving window of the platform works continuously, which is contradictory to the one-transmitting and one-receiving working state of the SAR, and there is no related achievement of single-station SAR passive positioning of moving ships at present. SUMMARY

[0005] Therefore, the present application provides a single-station moving ship active and passive cooperative positioning method based on relaxation transformation. The problems of the traditional single-station SAR active detection of the moving ship, such as the azimuth deviation and the loss of position caused by the interference of the ship-borne radar, are solved, and the problem that the existing repositioning relies on the SAR image of the ship and cannot realize the accurate positioning of the ship in a complex scene is solved.

[0006] The first aspect of the application provides a single-station moving ship active and passive cooperative positioning method based on relaxation transformation, comprising the following steps: S1, a single-station synthetic aperture radar receives multiple frames of radiation pulse signals from a target ship along the azimuth direction, processes the multiple frames of radiation pulse signals to obtain the pulse repetition interval sum, the time difference of arrival measurement value and the Doppler phase measurement value of the target ship, wherein each frame of radiation pulse signal contains multiple pulses; S2, according to the time difference of arrival measurement value and the Doppler phase measurement value, the passive measurement matrix of the target ship is determined; S3, based on the relationship between the pulse repetition interval sum and the speed constraint value and the position constraint value of the target ship, the theoretical measurement matrix of the target ship is determined; based on the theoretical measurement matrix and the passive measurement matrix, a positioning model of the target ship is constructed; S4, after linearization processing of the weighted least squares positioning model, the convex optimization positioning model is obtained by semi-positive relaxation transformation algorithm, and the target ship's predicted position and predicted speed are obtained by solving the convex optimization positioning model; S5, the single-station synthetic aperture radar transmits radar waves to the predicted position periodically through time division multiplexing mechanism to obtain the radar echo of the predicted position while receiving the radiation pulse signals of the target ship, and the radar echo is framed within the preset error range of the predicted position to obtain the scene echo of the target ship; wherein the pointing direction of the transmitted radar beam can be dynamically adjusted according to the real-time predicted position and predicted speed; S6, a matched filter is designed based on the predicted speed and the Doppler phase measurement value, the scene echo is coarsely focused by the matched filter to obtain focused echo, the peak signal in the focused echo is extracted, and the target ship's echo signal is obtained by inverse focusing inversion of the peak signal; S7, the target ship is imaged using the Doppler phase information contained in the echo signal, and the actual position of the target ship is determined according to the imaging result.

[0007] Further, the processing of the multiple frames of radiation pulse signals comprises compressing the bandwidth of the multiple frames of radiation pulse signals.

[0008] Further, the pulse repetition interval sum of the target ship is the sum of the time interval between each frame of the multiple frames of radiation pulse signals and the time interval between the multiple pulses in each frame of radiation pulse signal.

[0009] Further, the time difference of arrival measurement value comprises: taking the first pulse in the first frame of the multiple frames of radiation pulse signals as the reference time; taking the time when the first pulse of each frame of the multiple frames of radiation pulse signals arrives at the single-station synthetic aperture radar as the arrival time; subtracting the pulse repetition interval sum and the reference time from the arrival time to obtain the time difference of arrival measurement value.

[0010] Further, the Doppler phase measurement value comprises: applying non-uniform Fourier transform to calculate the peak phase of the first pulse of each frame of the multiple frames of radiation pulse signals.

[0011] Further, the positioning model of the target ship comprises: being realized by constructing a maximum likelihood estimation with an error between a theoretical measurement matrix and a passive measurement matrix as an objective function; the maximum likelihood estimation of the objective function is constrained by a speed constraint value and a position constraint value of the target ship; the speed constraint value and the position constraint value are both determined by a physical relationship between the monostatic synthetic aperture radar and the target ship.

[0012] Further, the theoretical measurement matrix comprises a theoretical time difference of arrival measurement value and a theoretical Doppler phase value of the target ship; wherein the theoretical Doppler phase value is related to a carrier frequency of the radiated pulse signal, a speed of light, a satellite geocentric geodetic coordinate system coordinate, the speed constraint value and the position constraint value of the target ship; and the theoretical time difference of arrival measurement value is related to the satellite geocentric geodetic coordinate system coordinate, the speed of light and the speed constraint value and the position constraint value of the target ship.

[0013] Further, in step S6, the peak signal in the focused echo is extracted by performing coarse focusing processing on the scene echo through a matched filter to obtain the focused echo, so that the actual position of the target ship forms a peak signal in the focused echo.

[0014] Further, the peak signal is inversely focused and inverted to obtain the echo signal of the target ship, comprising: the inverse focusing inversion is an inverse operation of the coarse focusing processing, and the echo signal of the target ship is inversely deduced from the peak signal through the inverse focusing inversion.

[0015] Further, the scene echo of the target ship comprises a mixed signal of a region where the target ship is located and a region where other ships except the target ship are located.

[0016] According to the single-station moving ship active and passive cooperative positioning method based on relaxation transformation provided in the present application, the following technical effects can be achieved:

[0017] (1) By approximately compensating the time difference of arrival and the signal parameters of the radiated source within the transmission window, the problem of positioning the moving ship under the incomplete observation of the single-station SAR is solved, and the dependence of the existing single-station moving ship positioning method on the transmission time of the radiated source and the complete reception of the signal is reduced;

[0018] (2) By constructing a non-convex positioning model by simultaneously solving TDOA and Doppler phase, and applying weighted least squares method and semi-definite relaxation algorithm to convert the non-convex positioning model into a convex optimization problem, the problems of local optimal solution and complex calculation cost caused by the non-convex positioning model can be solved;

[0019] (3) The method uses the positioning result of the single-station SAR passive detection of the moving ship as prior information, and completes ship echo detection and extraction through coarse focusing and peak value search, and uses the Doppler phase in the extracted ship echo to image the ship, realizes active and passive cooperative positioning, solves the dependence of the existing ship repositioning method on the visibility of the ship in the SAR image, and can realize accurate positioning of the target ship under the influence of complex sea conditions, three-dimensional motion of the ship, interference and other factors. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A flowchart of a single-station moving ship active and passive cooperative positioning method based on relaxation transformation according to an embodiment of the present application is schematically shown. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary and is not intended to limit the scope of the present application. In the following detailed description of the embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have been omitted or simply referenced in order not to obscure the concept of the present application.

[0023] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The terms "include", "comprise" and the like used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0024] All terms used herein, including technical and scientific terms, have meanings commonly understood by one of ordinary skill in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the specification, and should not be interpreted in an idealized or overly formal manner.

[0025] The present application provides a single-station moving ship active and passive cooperative positioning method based on relaxation transformation, which solves the problems of active detection of ship azimuth deviation and passive detection of low positioning accuracy, and reduces the positioning complexity.

[0026] Figure 1 A flowchart of a single-station moving ship active and passive cooperative positioning method based on relaxation transformation according to an embodiment of the present application is schematically shown.

[0027] As Figure 1As shown, the single station motion ship active and passive cooperative positioning method based on relaxation transformation according to the embodiment comprises steps S1-S7.

[0028] In step S1, the single station synthetic aperture radar receives multiple frames of radiation pulse signals from the target ship along the azimuth direction, processes the multiple frames of radiation pulse signals to obtain the pulse repetition interval sum, the time difference of arrival measurement value and the Doppler phase measurement value of the target ship, wherein each frame of radiation pulse signal contains multiple pulses.

[0029] In the embodiment, processing the multiple frames of radiation pulse signals comprises compressing the bandwidth of the multiple frames of radiation pulse signals.

[0030] Specifically, the multiple frames of radiation pulse signals are converted to the frequency domain / time-frequency domain by Fourier transform or wavelet transform, low-energy components are removed, and high-energy key spectrum is retained, so as to compress the bandwidth of the multiple frames of radiation pulse signals.

[0031] In the embodiment, the pulse repetition interval (PRI) sum of the target ship is the sum of the time interval sum between each frame of the multiple frames of radiation pulse signals and the time interval sum between the multiple pulses in each frame of radiation pulse signal.

[0032] Specifically, the pulse repetition interval sum can be expressed as:

[0033]

[0034] In the formula, n is the frame number, and n is a positive integer; is the time interval sum between the multiple pulses in the n frames of radiation pulse signals, that is, the PRI sum in the SAR receiving window, and re represents the receiving window; is the time interval sum between each frame of the n+1 frames of radiation pulse signals, that is, the PRI sum in the SAR transmitting window, and nre represents the transmitting window.

[0035] In the embodiment, the calculation method of the time difference of arrival measurement value comprises: taking the first pulse in the first frame of the multiple frames of radiation pulse signals as the reference time; taking the time when the first pulse of each frame of the multiple frames of radiation pulse signals arrives at the single station synthetic aperture radar as the arrival time; subtracting the pulse repetition interval sum from the arrival time and then subtracting the reference time to obtain the time difference of arrival measurement value. The above time difference measurement value constitutes a time difference measurement matrix.

[0036] Specifically, assuming that the first pulse in the first frame is taken as the reference time , and the time when the first pulse of the n frames of radiation pulse signals arrives at the SAR is the arrival time the time difference measurement value of the first pulse of the nth frame reaching the SAR is:

[0037]

[0038] wherein i represents the frame number.

[0039] Further, the time difference measurement values form a time difference measurement matrix , the time difference measurement matrix may be expressed as

[0040]

[0041] wherein T represents the transpose of the matrix.

[0042] In the present embodiment, the Doppler phase measurement value is calculated by applying a non-uniform Fourier transform to calculate the peak phase of the first pulse of each frame of the multi-frame radiation pulse signal.

[0043] Specifically, the Doppler phase measurement value of the nth frame of the radiation pulse signal may be expressed as:

[0044]

[0045] wherein is expressed as the radiation pulse signal of the target ship of the ith frame at the moment, and , is a non-uniform Fourier transform.

[0046] In the present embodiment, a Short-Time Fourier Transform (STFT) may also be used instead of the non-uniform Fourier transform to obtain the Doppler phase measurement value .

[0047] Further, the Doppler phase measurement values form a Doppler phase measurement matrix , the Doppler phase measurement matrix may be expressed as:

[0048]

[0049] In step S2, according to the time difference measurement values and the Doppler phase measurement values calculated above, a passive measurement matrix of the target ship is determined.

[0050] Specifically, the time difference measurement matrix And Doppler phase measurement matrix The passive measurement matrix D of the target vessel can be obtained:

[0051]

[0052] In step S3, based on the sum of pulse repetition intervals and the relationship between the velocity constraint value and the position constraint value of the target vessel, the theoretical measurement matrix of the target vessel is determined; based on the theoretical measurement matrix and the passive measurement matrix, the positioning model of the target vessel is constructed.

[0053] In this embodiment, the positioning model of the target vessel includes: constructing a maximum likelihood estimation with the error between the theoretical measurement matrix and the passive measurement matrix as the objective function; the maximum likelihood estimation of the objective function is constrained by the velocity constraint value v and the position constraint value p of the target vessel; both the velocity constraint value v and the position constraint value p are determined by the physical relationship between SAR and the target vessel.

[0054] The theoretical measurement matrix includes the theoretical time difference of arrival measurements of the target vessel. and theoretical Doppler phase value The theoretical Doppler phase value With the carrier frequency of the radiation pulse signal The speed of light c, the satellite's geocentric coordinate system coordinates s, and the target ship's velocity constraint value v and position constraint value p are all related; the theoretical time difference of arrival measurement value is also relevant. It is related to the satellite's geocentric coordinate system coordinates s, the speed of light c, and the target ship's velocity constraint value v and position constraint value p.

[0055] Specifically, the theoretical time difference of arrival measurement value for:

[0056]

[0057] Theoretical Doppler phase value for:

[0058]

[0059] Combine the above theoretical arrival time difference measurements and theoretical Doppler phase value The theoretical measurement matrix of the target ship can be obtained. .

[0060] Specifically, theoretical measurement matrix It can be represented as:

[0061]

[0062] Wherein, the satellite geocentric coordinates system is a geocentric coordinate system with the earth center as the origin, the x-axis pointing to the intersection of the prime meridian and the equator, the z-axis pointing to the north pole of the earth, and the y-axis forming a right-handed rectangular coordinate system with the x-axis and the z-axis. The satellite geocentric coordinates system coordinates will be updated in real time with the movement of the satellite.

[0063] In the embodiment, the above speed constraint value v and the position constraint value p are obtained by establishing prior information of the target ship .

[0064] Specifically, the prior information of the target ship is:

[0065]

[0066] Wherein, is the distance from the satellite to the earth center in the observation scene, is the relaxation amount, that is, the measurement error of the earth center distance, which is generally set by experience.

[0067] In order to simplify the motion model and reduce the complexity of the nonlinear problem, it is assumed that the position of the target ship does not move in a large range within the observation time.

[0068] In order to narrow down the parameter search range of the positioning model, avoid the algorithm converging to meaningless local optimal solution, and improve the stability and accuracy of positioning, the prior information of the target ship is used as a constraint to establish a constrained maximum likelihood estimation positioning model, and the specific model is as follows:

[0069]

[0070] Wherein, is the covariance matrix of .

[0071] In step S4, the above positioning model is linearized by using the weighted least squares method, and then converted into a convex optimization positioning model by using the semi-definite relaxation transformation algorithm. The convex optimization positioning model is solved to obtain the predicted position and predicted speed of the target ship.

[0072] Specifically, the above positioning model is first linearized by using the weighted least squares method (WLS):

[0073]

[0074] Wherein is the variable of the weighted least squares method, that is ; W is the weight matrix of the weighted least squares method, that is . and is the parameter matrix of the weighted least squares equation, corresponding to the linear term and the quadratic term coefficients of is the constant term vector, which is composed of the known parameters such as the satellite ECEF coordinates , the light speed , and the fixed terms of the reference signal.

[0075] By linearizing the above positioning model, the nonlinear positioning model can be approximated to a linearized weighted least squares positioning model.

[0076] Further, the above linearized positioning model is converted into a convex optimization positioning model by using a semi-definite relaxation transformation algorithm (SDR), and the convex optimization positioning model is solved to obtain the predicted position and the predicted velocity of the target ship. The specific model and solving process are as follows:

[0077]

[0078]

[0079]

[0080] wherein, is the SDR newly added variable, is the SDR coefficient matrix.

[0081] In addition, a convex optimization transformation method such as Second-Order Cone Programming (SOCP) can be used to replace the semi-definite relaxation transformation algorithm to solve the positioning model.

[0082] In step S5, the single station synthetic aperture radar transmits radar waves to the predicted position periodically through time division multiplexing mechanism to obtain the radar echo of the predicted position while receiving the target ship radiation pulse signal, and frames the radar echo within the preset error range of the predicted position to obtain the scene echo of the target ship. The pointing direction of the radar wave beam can be dynamically adjusted according to the real-time predicted position and the predicted velocity.

[0083] In this embodiment, the pointing direction of the SAR radar wave beam can be dynamically adjusted according to the real-time predicted position and the predicted velocity.

[0084] Specifically, according to the predicted position and the predicted velocity of the target ship, a radar wave beam pointing feedback system is established, including the following steps a-c.

[0085] Step a, in the satellite ECEF coordinate system (ECEF), the predicted position​ and predicted velocity Input into feedback system, according to signal processing delay (typical value 1~10ms), calculate position correction .

[0086] Step b, in satellite reference system (satellite body reference system), calculate beam pointing angle; first convert target position to satellite reference system:

[0087]

[0088] Wherein, is the predicted position in satellite reference system, is the rotation matrix from ECEF coordinate system to satellite reference system (determined by satellite orbit parameters and attitude), s is the position vector of satellite center of mass in ECEF coordinate system.

[0089] Further, according to the predicted position in satellite reference system Calculate the pitch angle in SAR beam pointing angle and azimuth angle .

[0090] Step c, according to the pitch angle and azimuth angle β, carry out beam control, if SAR is phased array antenna, generate phase weight matrix based on pitch angle and azimuth angle to carry out beam direction control and execution; if SAR is mechanical steering radar, drive servo motor to make antenna normal direction point to pitch angle and azimuth angle.

[0091] Based on the above radar wave beam pointing feedback system, SAR according to the calculated pitch angle and azimuth angle of the predicted position, while receiving the target ship's radiation pulse signal, periodically emits radar wave to the predicted position to obtain the radar echo of the predicted position.

[0092] Further, the radar echo received by SAR at the predicted position is framed within the preset error range to obtain the scene echo of the target ship.

[0093] Specifically, the preset error range is set according to the accuracy of the predicted position (passive positioning) result and the tolerance of positioning error in actual application scene, wherein the set preset error range is used to define the spatial area that may contain the target ship. For example, it can be set as a cube area with a side length of centered on the predicted position in three-dimensional space, and the preset error range is ​ The calculation is as follows:

[0094]

[0095] wherein, is a positioning error margin, which can be set according to experience, and is 300 m by default.

[0096] Further, the spatial cube is mapped to the echo domain (physical space to signal domain) through a range-Doppler model, and a corresponding relationship between the ship position and the SAR echo is constructed by using the range-Doppler model, so as to convert the position information in space into the corresponding echo data position in the original echo. The range-Doppler model is determined based on the working parameters of the SAR, the electromagnetic wave propagation characteristics, and the spatial characteristics of the geocentric and geodetic coordinate system.

[0097] Specifically, the mapping relationship is:

[0098]

[0099] wherein, is a range direction, is a maximum boundary of the predicted position error range in the range dimension, is a small boundary; is an azimuth direction time window, and then is the earliest observation time of the target in the azimuth direction, is the latest observation time; is the azimuth direction frequency in the SAR system; is a Doppler phase measurement error, which can be set according to the observation scene.

[0100] Further, in the radar echo obtained according to the above mapping relationship, a sub-matrix satisfying and in the radar echo matrix is extracted, that is, the scene echo of the target ship:

[0101]

[0102] wherein, is the scene echo of the target ship obtained by framing, is the matrix of the original echo, and Cube is a three-dimensional error cube mapping domain.

[0103] In step S6, a matched filter is designed based on the predicted speed and the Doppler phase measurement value, a scene echo is coarsely focused by the matched filter to obtain a focused echo, a peak signal in the focused echo is extracted, and the peak signal is inversely focused to obtain an echo signal of the target ship.

[0104] In the embodiment, the scene echo of the target ship further includes a mixed signal of the region where the target ship is located and the region where other ships except the target ship are located.

[0105] In the embodiment, the scene echo is coarsely focused by a matched filter to obtain a focused echo, and a peak signal in the focused echo is extracted, including:

[0106] The matched filter is matched with the phase characteristics in the scene echo, so that the scene echo is coarsely focused to obtain a focused echo, and the actual position of the target ship forms a peak signal in the focused echo.

[0107] The design target of the matched filter is to offset the Doppler frequency offset and phase divergence introduced by the target ship motion through phase compensation, so that the energy of the scene echo signal of the target ship is focused in the azimuth direction. In the embodiment, the design of the matched filter depends on the predicted speed and the Doppler phase measurement matrix obtained in the passive detection stage.

[0108] In the embodiment, the coarse focusing process is as follows:

[0109] First, the scene echo is preprocessed, and the scene echo is pulse compressed (distance expansion is eliminated), and the original echo characteristics in the azimuth direction are preserved, to prepare for azimuth direction matched filtering.

[0110] The matched filtering function is to perform complex convolution operation on the designed matched filter and the preprocessed echo, offset the Doppler phase offset introduced by the ship motion through phase compensation, and concentrate the ship echo energy in the azimuth direction, specifically:

[0111]

[0112] In the formula, is a fast Fourier transform, is an inverse fast Fourier transform, is a coarse focusing result, is a framed echo, is a filter function in the matched filter.

[0113] In the embodiment, an adaptive peak detection function is used to scan the coarse focusing result and extract signals whose amplitudes exceed a set threshold. The threshold is set according to the average noise level of the scene echo (e.g. 3-5 times the standard deviation of the noise), and the peak point is a local maximum in the azimuth direction and the distance direction.

[0114] Finally, the peak value is verified, and the peak position is extracted If the difference is less than or equal to the error range Δp, it is determined that the peak value corresponds to the target ship.

[0115] In addition, for the above-mentioned coarse focusing method, a Deramp algorithm or a CS algorithm (Chirp-Scaling) can also be used to coarsely focus the scene echo.

[0116] In the embodiment, the peak signal is inversely focused to obtain the echo signal of the target ship, including: the inverse focusing inversion is an inverse operation of the coarse focusing processing, and the echo signal of the target ship is inversely deduced from the peak signal through the inverse focusing inversion.

[0117] The specific formula is as follows:

[0118]

[0119] In the formula, is The ship echo obtained after the peak value is inversely focused is an inverse focusing function, is a peak searching function.

[0120] The above-mentioned inverse focusing inversion process includes focusing parameter extraction, inverse phase compensation, and echo signal reconstruction.

[0121] Specifically, the focusing parameter extraction is used to record the phase compensation parameters of the matched filter during coarse focusing, such as the Doppler phase measurement value; then, the inverse phase compensation is performed, that is, the extracted peak signal is subjected to the inverse phase compensation of the matched filter; finally, the echo signal reconstruction is performed, the inverse Fourier transform is performed on the signal after the inverse phase compensation, and the signal of the target ship in the original echo domain, that is, the echo signal of the target ship, is reconstructed.

[0122] In addition, the echo signal of the target ship after the inverse focusing inversion retains the subtle phase changes caused by the ship movement (such as the phase fluctuation caused by the three-dimensional movement and the sea wave disturbance), and these information will be further calibrated through the actively detected Doppler phase in the subsequent accurate imaging, and finally the high-precision positioning of the active and passive cooperation is realized.

[0123] In step S7, the target ship is imaged by using the Doppler phase information contained in the echo signal, and the actual position of the target ship is determined according to the imaging result.

[0124] Since the echo signal of the target ship is the original echo signal obtained after the coarse focusing peak extraction and the inverse focusing inversion, the Doppler phase contained in the original echo signal is a direct physical reflection of the ship movement state.

[0125] Further, by compensating the ship motion phase error contained in the Doppler phase, the ship echo is focused in the two-dimensional plane of range and azimuth with high resolution, providing a clear image reference for position determination, so as to realize accurate imaging.

[0126] After accurate imaging, the target ship appears as a high-energy focus point (or a continuous area matching the size of the ship) in the image, and its position can be converted into actual geographic coordinates by the following steps:

[0127] First, the image coordinates and geographic coordinates are mapped. The SAR imaging system can establish the mapping relationship between the image pixel coordinates and the geocentric coordinate system through ephemeris data (platform position, speed) and imaging geometric models (such as the range Doppler model).

[0128] Further, the center pixel (or energy center of gravity) of the ship focusing area is identified, and its image coordinates are extracted and substituted into the above mapping relationship to calculate the corresponding satellite geocentric coordinate system coordinates, which are the actual geographic position of the target ship.

[0129] The calculated actual geographic position is checked for consistency in combination with the passive positioning result. If there is a small deviation (usually caused by residual phase error), the geometric parameters in the mapping relationship can be optimized by least squares iteration to further correct the position result and ensure that the positioning error is as low as possible.

[0130] Through the above steps S1 to S7, the final output of the actual position of the target ship not only contains the accurate satellite geocentric coordinate system coordinates of the ship, but also carries the high-resolution imaging result, providing dual data support for subsequent target recognition, trajectory tracking and other applications.

[0131] Those skilled in the art can understand that the features described in various embodiments of the present application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present application. In particular, the features described in various embodiments of the present application can be combined and / or combined in various ways without departing from the spirit and teachings of the present application. All these combinations and / or combinations fall within the scope of the present application.

[0132] The embodiments of the present application are described above. However, these embodiments are only for illustrative purposes, and are not intended to limit the scope of the present application. Although each embodiment is described above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Without departing from the scope of the present application, those skilled in the art can make various alternatives and modifications, which should fall within the scope of the present application.

Claims

1. A method for passive and active cooperative positioning of a moving ship based on relaxation transformation, characterized in that, The method comprises the following steps: S1, a single station synthetic aperture radar receives multiple frames of radiation pulse signals from a target ship in an azimuth direction, processes the multiple frames of radiation pulse signals to obtain a pulse repetition interval sum, a time difference of arrival measurement value and a Doppler phase measurement value of the target ship, wherein each frame of the radiation pulse signals contains multiple pulses; S2, a passive measurement matrix of the target ship is determined according to the time difference of arrival measurement value and the Doppler phase measurement value; S3, a theoretical measurement matrix of the target ship is determined based on a relationship between the pulse repetition interval sum and a speed constraint value and a position constraint value of the target ship; a positioning model of the target ship is constructed based on the theoretical measurement matrix and the passive measurement matrix; S4, after linearizing the positioning model by using a weighted least squares method, the positioning model is converted into a convex optimization positioning model by a semi-positive relaxation transformation algorithm, the convex optimization positioning model is solved to obtain a predicted position and a predicted speed of the target ship; S5, the single station synthetic aperture radar periodically transmits radar waves to the predicted position to obtain radar echoes of the predicted position and frame selects the radar echoes within a preset error range of the predicted position to obtain scene echoes of the target ship by using a time division multiplexing mechanism while receiving the radiation pulse signals of the target ship; a direction of a beam of the radar waves can be dynamically adjusted according to the predicted position and the predicted speed in real time; S6, a matched filter is designed based on the predicted speed and the Doppler phase measurement value, the scene echoes are coarsely focused by using the matched filter to obtain focused echoes, peak signals in the focused echoes are extracted, and the peak signals are inversely focused to obtain echo signals of the target ship; S7, the target ship is imaged by using Doppler phase information contained in the echo signals, and an actual position of the target ship is determined according to an imaging result.

2. The method of claim 1, wherein, The processing of the multiple frames of radiation pulse signals comprises compressing a bandwidth of the multiple frames of radiation pulse signals.

3. The method of claim 1, wherein, The pulse repetition interval sum of the target ship is a sum of a time interval sum between each frame of the multiple frames of radiation pulse signals and a time interval sum between the multiple pulses in each frame of radiation pulse signals.

4. The method of claim 1, wherein, The calculation method of the time difference of arrival measurement value comprises: a first pulse in a first frame of the multiple frames of radiation pulse signals is taken as a reference time, a time when a first pulse of each frame of the multiple frames of radiation pulse signals arrives at the single station synthetic aperture radar is taken as an arrival time, and the arrival time is subtracted by the pulse repetition interval sum and then subtracted by the reference time to obtain the time difference of arrival measurement value.

5. The method of claim 1, wherein, The calculation method of the Doppler phase measurement value comprises: a non-uniform Fourier transform is applied to calculate a peak phase of a first pulse of each frame of the multiple frames of radiation pulse signals.

6. The method of claim 1, wherein, The positioning model of the target ship comprises: a maximum likelihood estimation is constructed by taking an error between the theoretical measurement matrix and the passive measurement matrix as an objective function; and The maximum likelihood estimation of the objective function is constrained by the speed constraint value and the position constraint value of the target ship; Both the speed constraint value and the position constraint value are determined by the physical relationship between the monostatic synthetic aperture radar and the target ship.

7. The method of claim 6, wherein, The theoretical measurement matrix is composed of a theoretical time difference of arrival measurement value and a theoretical Doppler phase measurement value of the target ship; The theoretical Doppler phase measurement value is related to the carrier frequency of the radiation pulse signal, the speed of light, the satellite's geocentric geodetic coordinate, the speed constraint value and the position constraint value of the target ship; The theoretical time difference of arrival measurement value is related to the satellite's geocentric geodetic coordinate, the speed of light, and the speed constraint value and the position constraint value of the target ship.

8. The method of claim 1, wherein, In step S6, the scene echo is coarsely focused by the matched filter to obtain a focused echo, and the peak signal in the focused echo is extracted, including: The matched filter is matched with the phase characteristics in the scene echo to coarsely focus the scene echo to obtain a focused echo, so that the actual position of the target ship forms the peak signal in the focused echo.

9. The method of claim 1, wherein, The peak signal is inversely focused to obtain the echo signal of the target ship, including: The echo signal of the target ship is inversely deduced from the peak signal by the inverse focusing inversion; The inverse focusing inversion is the inverse operation of the coarse focusing processing.

10. The method of claim 1, wherein, The scene echo of the target ship includes mixed signals of the area where the target ship is located and other ships except the target ship.

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