A mid-orbit multi-channel SAR ground moving target motion parameter estimation method

Abstract

The application relates to a medium earth orbit (MEO) multi-channel SAR ground moving target motion parameter estimation method and belongs to the field of radar signal processing. A signal model of a distance equation of a first channel and a second channel of MEO SAR based on third-order Taylor expansion is established, a first-order phase coefficient, a second-order phase coefficient, a third-order phase coefficient and an intermediate parameter are estimated based on a CPF method, along-course velocity and radial acceleration in the second-order phase coefficient are adjusted by combining multi-channel information, and along-course velocity, radial velocity, along-course acceleration and radial acceleration of the target are estimated based on a coupling relationship. The method solves the problem of difficult motion parameter estimation of a moving target caused by the coupling relationship.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radar signal processing, in particular to a medium-orbit synthetic aperture radar moving target motion parameter estimation method. BACKGROUND

[0002] Medium-Earth-Orbit Synthetic Aperture Radar (MEOSAR) has the advantages of wide coverage, short revisit period, strong anti-destruction ability, etc., and is suitable for air-to-ground wide-area reconnaissance and time-sensitive target (such as ground moving target) monitoring.

[0003] Compared with the traditional Low-Earth-Orbit (LEO) synthetic aperture radar, the complex relative motion geometry between the MEO SAR and the target leads to a complex coupling relationship between the velocity, acceleration and position of the target, which brings many difficulties to the motion parameter estimation of the moving target, and makes the target motion parameter estimation method suitable for the traditional LEO SAR cannot be directly used for MEO SAR. Therefore, it is urgent to study an accurate motion parameter estimation method that can be used for MEO SAR. SUMMARY

[0004] The technical problem to be solved by the present application is:

[0005] In order to solve the problem that the complex relative motion geometry between the MEO SAR and the target leads to a complex coupling relationship between the velocity, acceleration and position of the target, which brings many difficulties to the motion parameter estimation of the moving target, the present application provides a medium-orbit multi-channel SAR ground moving target motion parameter estimation method.

[0006] In order to solve the above technical problem, the technical scheme adopted by the present application is:

[0007] A medium-orbit multi-channel SAR ground moving target motion parameter estimation method, characterized in that the along-track velocity v ta , the radial velocity v tr , the along-track acceleration a ta and the radial acceleration a tr of the target are estimated by using the cubic phase function (CPF) method; the steps are as follows:

[0008] Step 1: for the reference channel signal, the values of the quadratic phase coefficient l2 and the cubic phase coefficient l3 in the signal phase history are estimated by performing CPF on the signal, and the value of the linear phase coefficient l1 in the signal phase is obtained by demodulating the signal of the reference channel using the estimated values of l2 and l3;

[0009] Step 2: For the signal of the second channel, use the estimated values ​​of l2 and l3 of the reference channel to demodulate the signal of the second channel to obtain the estimated value of the intermediate parameter α;

[0010] Step 3: Estimate the radial velocity v using the following formula tr and acceleration along the heading a ta Value:

[0011]

[0012]

[0013] Among them, superscript R0 represents the estimated value; R0 is the value of t. a = The distance the radar reaches the target at time 0; t a It's about location and time; v s0 Is the radar at t a = velocity at time 0; a sa This indicates the radar's acceleration along the heading; j sr Indicates the radial jerk of the radar;

[0014] Step 4: Estimate the speed v along the heading using the following formula ta The value;

[0015]

[0016] Among them, a sr Indicates the radial acceleration of the radar;

[0017] Step 5: Use the results estimated in Steps 3 and 4 to estimate the radial acceleration a. tr Value:

[0018]

[0019] Among them, v t0 The target is at t a = Velocity at time 0.

[0020] A further technical solution of the present invention: The formulas for estimating the values ​​of the second-order phase coefficient l2 and the third-order phase coefficient l3 in the signal phase history in step 1 are as follows:

[0021] Third-order phase signal s(t) a The IFR of ) is

[0022]

[0023] Select t a1 =0, t a2 =0.11N to estimate l2 and l3, where N is T aThe length of the reference channel, and lambda represents the wavelength of the radar signal.

[0024] The further technical solution of the present application: step 1 obtains the value of the linear phase coefficient l1 in the signal phase by demodulating the signal of the reference channel using the estimated values of l2 and l3, and the formula is as follows:

[0025]

[0026] Wherein, T a represents the synthetic aperture time, s1(t a ) represents the reference channel signal.

[0027] The further technical solution of the present application: step 2 estimates the value of the intermediate parameter alpha, and the formula is as follows:

[0028]

[0029] Wherein, q1 is the estimated value of l1+dalpha, s2(t a ) represents the signal of the second channel, and d represents the channel interval.

[0030] A computer system, characterized by comprising: one or more processors, a computer readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the above method.

[0031] A computer readable storage medium, characterized by storing computer executable instructions, the instructions when executed are used to implement the above method.

[0032] The beneficial effects of the present application are:

[0033] The present application provides a kind of middle orbit multi-channel SAR ground moving target motion parameter estimation method, for the complex relative motion geometry between MEOSAR and target, which leads to the existence of complex coupling relationship between the velocity, acceleration and position of target, using the spatial freedom provided by multi-channel to release the coupling between target velocity and acceleration, can realize the accurate estimation of accelerated target motion parameter, solve the problem of motion target motion parameter estimation difficulty caused by coupling relationship. The middle orbit multi-channel SAR ground moving target motion parameter estimated by the method of the present application can provide technical support for the further development of middle orbit multi-channel SAR-GMTI system. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings are only for the purpose of illustrating specific embodiments and are not considered to be limiting of the present application, and in the entire drawings, the same reference signs represent the same components.

[0035] Figure 1A flow chart of the process of the present application.

[0036] Figure 2 A flow chart of step 2 of the present application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0038] The embodiments of the present application propose a motion parameter estimation method for a medium orbit multi-channel SAR using a cubic phase function (CPF) and the degrees of freedom of a multi-channel system. It includes the following two parts:

[0039] 1) Obtain the signal model of each channel of the MEO SAR based on the third-order range equation

[0040] By using vector projection and vector derivation principles, the third-order approximate range equation of the medium orbit multi-channel SAR is obtained:

[0041]

[0042] wherein,

[0043] l1≈v tr (2)

[0044]

[0045]

[0046]

[0047] wherein, t a is the azimuth slow time; R0 is the distance from the radar to the target at t a =0; v s0 and v t0 are the speeds of the radar and the target at t a =0, respectively. In addition, v tr and a tr represent the radial speed and the radial acceleration of the target, respectively; v sr , a sr and j sr represent the radial speed, the radial acceleration and the radial jerk of the radar, respectively; v ta and a taThe target's velocity and acceleration along the heading are defined; a sa This indicates the radar's acceleration along the heading.

[0048] Assuming the radar transmits a cubic phase signal, the signal after demodulation and range compression can be expressed as:

[0049]

[0050] Where λ represents the wavelength of the radar signal, T a Indicates the time for synthesizing the aperture.

[0051] 2) Based on the signal model obtained in step 1, the target's heading velocity v is estimated using the CPF method and in conjunction with multi-channel information. ta Radial velocity v tr acceleration along the heading a ta and radial acceleration a tr .like Figure 2 As shown, it includes the following steps:

[0052] (a) For the reference channel signal, the values ​​of l2 and l3 are estimated by performing CPF on the signal, and the value of l1 is obtained by demodulating the reference channel signal using the estimated values ​​of l2 and l3;

[0053] (b) For the signal of the second channel, the estimated values ​​of l2 and l3 of the reference channel obtained in (a) are used to demodulate the signal of the second channel to obtain the value of α;

[0054] (c) Estimating the radial velocity v using formulas (7) and (8) tr and acceleration along the heading a ta The value, note the superscript.

[0055] Indicates an estimated value;

[0056]

[0057]

[0058] (d) Use formula (9) to estimate the speed v along the heading. ta The value;

[0059]

[0060] (e) Use the results estimated in steps (c) and (d) to estimate a tr The value of .

[0061]

[0062] Figure 1 This is a flowchart illustrating the present invention. The specific steps of the present invention are as follows:

[0063] Step 1: Obtain the signal model of the first and second channels of MEO SAR based on the third-order Taylor expansion of the range equation.

[0064] Assuming the radar transmits a third-order phase signal, the reference channel signal after demodulation and range compression can be expressed as follows:

[0065]

[0066] In the formula,

[0067]

[0068] l1 = v tr (13)

[0069]

[0070]

[0071] Among them, R c,1 (t a ) represents the third-order Taylor approximation distance equation. It can be seen that if the linear phase coefficient l1 in the signal phase can be estimated, then according to formula (13), the radial velocity v tr The radial acceleration a can be estimated by formula (14) if the secondary phase coefficient l2 in the signal phase history can be estimated. tr and speed along the heading v ta The relationship; if the third phase coefficient l3 in the signal phase history is estimated, then the acceleration a along the heading can be estimated according to formula (15). ta The problem of accelerating the estimation of target parameters is transformed into the problem of estimating the linear coefficients, quadratic coefficients, and third-order coefficients in the phase history of a third-order phase signal.

[0072] However, although l2 was estimated, the target radial acceleration a was obtained. tr and speed along the heading v ta The relation is given, but it is still impossible to obtain a. tr and v ta The value of a, because a tr and v ta Coupling exists in l2 (see Equation 14). To address this issue, additional information needs to be utilized to decouple the components. The decoupling scheme is described below.

[0073] In a medium-orbit multi-channel SAR-GMTI system, the signal of the second channel after demodulation and range compression can be represented as follows:

[0074]

[0075] In the formula,

[0076]

[0077]

[0078]

[0079]

[0080] Among them, R c,2 (t a Let represent the third-order Taylor approximate distance equation for the second channel. It can be seen that the linear coefficients l1+dα of the second channel are related to the radial velocity v. tr and speed along the heading v ta The relationship is as follows. If the linear phase l1+dα in the signal phase history of the second channel can be estimated, the radial velocity v can be obtained. tr and speed along the heading v ta The relationship. The coefficients of the first channel are estimated. and Then, the CPF algorithm steps are repeated for the signal in the second channel to obtain the linear phase l1+dα of the second channel. By jointly using the information of l1, l2, l3, and l1+dα, the decoupled velocity and acceleration information can be obtained.

[0081] Step 2: Based on the first two-channel signal model obtained in Step 1, the target's heading velocity v is estimated using the CPF method. ta Radial velocity v tr acceleration along the heading a ta and radial acceleration a tr .

[0082] Based on equation (16), the third-order phase signal s(t) a The instantaneous frequency ratio (IFR) is:

[0083]

[0084] If we can know the IFR at two times t a If the value of t is found, then l2 and l3 can be determined. Choose t. a1 =0, t a2 =0.11N (N is T) aThe lengths of l2 and l3 are used to estimate l2 and l3. Once l2 and l3 are estimated, l1 and l1+dα can be estimated by second-phase demodulation using the estimates of l2 and l3.

[0085] The steps for estimating the motion parameters of an accelerating target using CPF are as follows:

[0086] (a) Let t a1 and t a2 Let the values ​​be 0 and 0.11N respectively, and estimate t using formula (22). a1 =0 and t a2 The two IFR values ​​corresponding to ≈0.11N and

[0087]

[0088] (b) Order but

[0089]

[0090] (c) Using the estimated and The signal in the reference channel is demodulated in second order to obtain an estimate of l1.

[0091]

[0092] (d) Profit calculated and The signal in the second channel is demodulated in second order to obtain an estimate of α.

[0093]

[0094] Where q1 is the estimated value of l1+dα.

[0095] (e) Estimate the radial velocity v using formulas (7), (8), (9) and (10). tr Radial acceleration a tr acceleration along the heading a ta and speed along the heading v ta .

[0096] The system parameters of the medium-orbit multi-channel SAR are shown in Table 1, and the target parameters are shown in Table 2. Table 3 gives the v tr v ta a tr and a ta The estimation error results are shown in Table 3. As can be seen from the table, the estimation errors are all very small, which indicates that the estimation accuracy of the present invention is very high.

[0097] Table 1 Parameters of MEO Multichannel SAR System

[0098] Orbital height 6,000 km Distance bandwidth 30 MHz Sampling frequency 40 MHz Azimuth resolution 6m Illumination time 3.3s Earth radius 6,371 km [R0] 7,548.7 km Pulse repetition frequency 1,400 Hz Argument of perigee 0 Longitude of ascending node 0 Eccentricity 0 Greenwich hour angle at zero time 0 Orbital inclination 90° Wavelength 0.03m Channel spacing d 2m

[0099] Table 2 Target Parameters

[0100] Target v ta (m / s) v tr (m / s) a ta (m / s 2 )]]> a tr (m / s 2 )]]> Target 1 8 13 0.2 0.3 Target 2 15 6 -0.3 0.4 Target 3 7 14 0.15 -0.5

[0101] Table 3 Estimation Error

[0102]

[0103] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for estimating motion parameters of a ground moving target using medium-orbit multi-channel SAR, characterized in that, The target's yaw velocity v is estimated using the cubic phase function (CPF) method. ta Radial velocity v tr acceleration along the heading a ta and radial acceleration a tr The steps are as follows: Step 1: For the reference channel signal, estimate the values ​​of the second phase coefficient l2 and the third phase coefficient l3 in the signal phase history by performing CPF on the signal. Use the estimated values ​​of l2 and l3 to demodulate the reference channel signal to obtain the value of the linear phase coefficient l1 in the signal phase. Step 1 uses the estimated values ​​of l2 and l3 to demodulate the signal in the reference channel to obtain the value of the linear phase coefficient l1 in the signal phase. The formula is as follows: Among them, T a Represents the synthesis aperture time, s1(t) a () indicates the reference channel signal; Step 2: For the signal of the second channel, use the estimated values ​​of l2 and l3 of the reference channel to demodulate the signal of the second channel to obtain the estimated value of the intermediate parameter α; Step 2: The formula for estimating the value of the intermediate parameter α is as follows: Where q1 is an estimate of l1+dα, s2(t a ) represents the signal of the second channel, and d represents the channel spacing; Step 3: Estimate the radial velocity v using the following formula tr and acceleration along the heading a ta Value: Among them, superscript R0 represents the estimated value; R0 is the value of t. a = The distance the radar reaches the target at time 0; t a It's about location and time; v s0 Is the radar at t a = velocity at time 0; a sa This indicates the radar's acceleration along the heading; j sr Indicates the radial jerk of the radar; Step 4: Estimate the speed v along the heading using the following formula ta The value; Among them, a sr Indicates the radial acceleration of the radar; Step 5: Use the results estimated in Steps 3 and 4 to estimate the radial acceleration a. tr Value: Among them, v t0 The target is at t a = Velocity at time 0.

2. The method for estimating motion parameters of a ground moving target using medium-orbit multi-channel SAR according to claim 1, characterized in that, Step 1 estimates the values ​​of the second-order phase coefficient l2 and the third-order phase coefficient l3 in the signal phase history. The formulas are as follows: Third-order phase signal s(t a The IFR of ) is Select t a1 =0, t a2 =0.11N to estimate l2 and l3, where N is T a The length of λ represents the wavelength of the radar signal.

3. A computer system, characterized in that... include: One or more processors, a computer-readable storage medium for storing one or more programs, wherein, when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method of claim 1.

4. A computer-readable storage medium, characterized in that... The device stores computer-executable instructions, which, when executed, are used to implement the method of claim 1.

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