Earth-based radar-to-moon three-dimensional imaging error estimation and compensation method based on error parameterization modeling and estimation

Abstract

The invention relates to a moon three-dimensional imaging error estimation and compensation method for a ground-based radar based on error parameterization modeling and estimation, and belongs to the technical field of synthetic aperture radars. The method comprises the following steps: step 1, establishing a time delay error model of various error sources in earth-moon imaging, and determining a variation range of error parameters in an observation time period according to the time delay error model; step 2, establishing an objective function of an earth-moon multi-track SAR observation optimization model based on the minimum image entropy, determining optimization variables, and determining constraint conditions according to the variation range of the error parameters; and step 3, solving the objective function established in the step 2 to obtain an estimated value of the time delay error, and compensating the time delay error to carry out earth-moon high-resolution three-dimensional imaging.

Description

Technical Field

[0001] The invention relates to a method for estimating and compensating errors of ground-based radar three-dimensional moon imaging based on error parameterized modeling and estimation, and belongs to the technical field of synthetic aperture radar. Background Art

[0002] Ground-based synthetic aperture radar (GB SAR) is a radar system built on the earth for high-resolution imaging of the moon. It achieves lunar observation by sending and receiving electromagnetic waves to the moon from the earth. Compared with other methods of lunar observation such as optical remote sensing, ground-based radar observation has the advantages of all-day, all-weather, low cost, and high reusability. At present, GB SAR shows great potential. For example, it can achieve high-resolution imaging of the moon, thereby providing support for lunar geological science research, formulation and implementation of lunar exploration projects, etc. However, with the continuous improvement of the requirements of corresponding scientific research tasks, these applications require GB SAR to obtain more comprehensive and accurate information on the lunar surface, which puts forward more stringent requirements on the GB SAR lunar imaging system.

[0003] In Earth-Moon imaging, there are various complex error sources, including atmospheric propagation error, stop-and-go assumption error, radar sampling position error, ephemeris accuracy error, etc. These error sources will introduce radar echo delay error, thereby deteriorating the SAR imaging quality. Under the condition of long synthetic aperture time within the orbit, high-order delay error will cause defocusing of imaging within the orbit; under the condition of large temporal and spatial differences between orbits, the imaging offsets of each orbit caused by low-order delay error are different, resulting in defocusing of joint imaging between orbits. In order to achieve high-resolution three-dimensional imaging, it is necessary to accurately compensate for the delay error introduced by various error sources in Earth-Moon imaging. At present, there is no suitable error estimation and compensation method for Earth-Moon three-dimensional imaging that can accurately compensate for various complex error sources and provide support for GB SAR three-dimensional high-resolution imaging of the moon. Summary of the invention

[0004] In view of this, the present invention proposes a method for estimating and compensating the error of ground-based radar three-dimensional lunar imaging based on error parameterized modeling and estimation, thereby realizing high-resolution three-dimensional imaging of the Earth and the Moon.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for estimating and compensating errors of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation, the method comprising the following steps:

[0007] Step 1: Establish a time delay error model for various error sources in Earth-Moon imaging, and determine the variation range of error parameters during the observation period according to the time delay error model;

[0008] Step 2: Establishing the objective function of the Earth-Moon multi-orbit SAR observation optimization model based on minimum image entropy, determining the optimization variables, and determining the constraint conditions according to the variation range of the error parameters;

[0009] Step 3: Solve the objective function established in step 2 to obtain an estimate of the time delay error, and compensate for the time delay error to perform high-resolution three-dimensional imaging of the Earth and the Moon.

[0010] Optionally, various error sources in the Earth-Moon imaging described in the present invention include tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and azimuth sampling delay error.

[0011] Optionally, the delay error model of the present invention is:

[0012]

[0013] in, They represent the echo delay error introduced by tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and radar sampling position error, respectively. Indicates the echo delay under ideal conditions.

[0014] Optionally, the present invention uses a high-order polynomial to fit the time delay error of each track under a long synthetic aperture time according to atmospheric parameters and Earth-Moon observation configuration files, and estimates the variation range of the time delay error parameters of each track.

[0015] Optionally, the objective function of the present invention is:

[0016]

[0017] τ estimate (j,k,l,n,v i )=τ ideal (j,k,l,n)+v i ·T(n)

[0018] T(n)=[1nPRT(nPRT) 2 ...] T

[0019] Among them, (j, k, l) represents the three-dimensional grid points, v is the variable to be optimized, and each vector v in v i The elements in represent the polynomial error parameters in the delay error of each track;

[0020] The constraints are:

[0021] v=[v 1 ;v 2 ;...v N ]∈D v (4)

[0022] Among them, n represents the corresponding azimuth time in each baseline, N a Indicates the total number of azimuth sampling points for each baseline, D v represents the variation range of the error parameter estimated according to the time-varying error model, PRT represents the radar azimuth sampling interval, τ ideal (j,k,l,n) represents the echo delay at the imaging grid point (j,k,l) ​​at azimuth time n under ideal conditions, s r i (τ estimate (j,k,l,n,v i ), n) represents the echo array after the range pulse compression, at the distance τ estimate (j,k,l,n,v i ) and echo data at time n.

[0023] Furthermore, in step three of the present invention, a particle swarm optimization algorithm is used to solve the objective function established in step two, and each particle is a multidimensional vector composed of polynomial parameters of the delay errors of each track.

[0024] Furthermore, step three of the present invention adopts an optimization strategy of first single-track search and then multi-track joint search to solve the objective function.

[0025] Beneficial effects:

[0026] The present invention uses an intelligent optimization algorithm to solve the Earth-Moon multi-track SAR observation optimization model, accurately estimates and compensates for the delay error, and thus performs high-resolution three-dimensional imaging of the Earth and the Moon, effectively overcoming the difficulties brought by various complex error sources in Earth-Moon imaging to high-resolution three-dimensional imaging. Computer simulation results and actual test results show that this method is feasible and has superior performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the ground-based radar signal transmission model under non-ideal factors in the present invention;

[0029] Figure 2(a) to Figure 2(c) 2(a) is a point target imaging result diagram before error compensation, FIG2(b) is a point target imaging result diagram after error compensation, and FIG2(c) is a point target imaging result diagram under ideal conditions;

[0030] Figure 3(a) to Figure 3(c) 3(a) is a diagram of the target imaging result before error compensation, FIG3(b) is a diagram of the target imaging result after error compensation, and FIG3(c) is a diagram of the target imaging result under ideal conditions. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] It should be noted that the following embodiments and features in the embodiments may be combined with each other in the absence of conflict; and, based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present disclosure.

[0033] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0034] First, starting from the formation mechanism of various error sources, the radar echo signal delay error models caused by tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and azimuth sampling delay error are established respectively. The schematic diagram of the ground-based radar signal transmission model under the influence of errors is shown in the figure. Figure 1 As shown. The ground-based radar echo signal model under the influence of these complex error sources can be modeled as:

[0035]

[0036] Among them, w r represents the distance window function, w a represents the azimuth window function, i represents the i-th radar track, t r Denotes distance to time, t a represents the azimuth time, k r represents the frequency modulation slope, f c represents the carrier frequency of electromagnetic waves, represents the echo delay error model corresponding to the i-th radar track. The delay error model can be further expressed as:

[0037]

[0038] in, They represent the echo delay error introduced by tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and radar sampling position error, respectively. Indicates the echo delay under ideal conditions.

[0039] After that, the minimum image entropy is used as the objective function, and the polynomial parameters of each order in the delay error of each track are used as optimization variables to establish the Earth-Moon multi-track SAR observation optimization model. The objective function in the optimization model can be modeled as follows:

[0040]

[0041] Among them, (j, k, l) represents the three-dimensional grid points, v is the variable to be optimized, which can be understood as a matrix composed of N vectors, each vector v i The elements in represent the polynomial error parameters in the delay error of each track.

[0042] The constraints of the optimization model can be modeled as:

[0043]

[0044] Among them, n represents the corresponding azimuth time in each baseline, N a Indicates the total number of azimuth sampling points for each baseline, D v represents the variation range of the error parameter estimated according to the time-varying error model, PRT represents the radar azimuth sampling interval, τ ideal (j,k,l,n) represents the echo delay at the imaging grid point (j,k,l) ​​at azimuth time n under ideal conditions, s r i (τ estimate (j,k,l,n,v i ), n) represents the echo array after the range pulse compression, at the distance τ estimate (j,k,l,n,v i ) and the echo data at time n. Formula (4) mainly explains the process of compensating the delay error based on the currently estimated error parameter and performing coherent accumulation based on the BP algorithm. Finally, the intelligent optimization algorithm is used to solve the optimization model, estimate and compensate the delay error.

[0045] Combined with the above analysis, the process of the error estimation and compensation method for ground-based radar three-dimensional lunar imaging based on error parameterization modeling and estimation proposed in this application will be introduced in detail below:

[0046] Step 1: Establish a time delay error model for various error sources in Earth-Moon imaging, and determine the variation range of error parameters during the observation period according to the time delay error model;

[0047] Firstly, a time delay error model of the error source is established from the mechanism. According to the atmospheric parameters and the Earth-Moon observation configuration file, a high-order polynomial is used to fit the time delay errors of each orbit under long synthetic aperture time, and the range of error parameters of the time delay error polynomial of each orbit is roughly estimated.

[0048] Step 2: Establishing the objective function of the Earth-Moon multi-orbit SAR observation optimization model based on minimum image entropy, determining the optimization variables, and determining the constraint conditions according to the variation range of the error parameters;

[0049] The error estimation and compensation of Earth-Moon multi-orbit SAR can be understood as an optimization problem with the goal of optimizing image quality. Therefore, an optimization model for Earth-Moon multi-orbit SAR observation can be established with the minimum image entropy as the objective function and the polynomial error parameters of each track as the optimization variables.

[0050] Step 3: Solve the objective function established in step 2 to obtain an estimated value of the time delay error, and compensate for the time delay error to perform high-resolution three-dimensional imaging of the Earth and the Moon;

[0051] This embodiment uses the particle swarm optimization (PSO) algorithm to solve the objective function established in step 2. Each particle is a multidimensional vector composed of polynomial parameters of the delay error of each track. In order to improve the final search effect and reduce the computational complexity, an optimization strategy of first searching a single track and then searching multiple tracks together can be adopted. The delay error is compensated according to the estimated values ​​of the polynomial parameters of the delay error of each track, and three-dimensional imaging is performed.

[0052] Example

[0053] Computer simulation was used to verify the effectiveness of the error estimation and compensation method for ground-based radar three-dimensional lunar imaging based on error parameterized modeling and estimation proposed in the present invention.

[0054] In the point target 3D imaging simulation verification, the point target imaging results before and after the proposed method error compensation and the point target imaging results after the proposed method error compensation and under ideal conditions are compared, as shown in Figure 2. The point target imaging quality evaluation results after error compensation and under ideal conditions are shown in Table 1.

[0055] Table 1 Comparison results of point target imaging quality after error compensation and under ideal conditions

[0056]

[0057] In the simulation verification of three-dimensional imaging of surface targets, the imaging results of surface targets before and after error compensation of the proposed method and the imaging results of surface targets after error compensation of the proposed method and under ideal conditions are compared, as shown in Figure 3.

[0058] In summary, the effectiveness of the method proposed in the present invention has been demonstrated through computer simulation.

[0059] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for estimating and compensating the error of ground-based radar three-dimensional lunar imaging based on error parameterization modeling and estimation, characterized in that: The method steps include: Step 1: Establish a time delay error model for various error sources in Earth-Moon imaging, and determine the variation range of error parameters during the observation period according to the time delay error model; Step 2: Establishing the objective function of the Earth-Moon multi-orbit SAR observation optimization model based on minimum image entropy, determining the optimization variables, and determining the constraint conditions according to the variation range of the error parameters; Step 3: Solve the objective function established in step 2 to obtain an estimate of the time delay error, and compensate for the time delay error to perform high-resolution three-dimensional imaging of the Earth and the Moon.

2. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation according to claim 1, characterized in that: Various error sources in the Earth-Moon imaging include tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and azimuth sampling delay error.

3. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation according to claim 2 is characterized in that: The delay error model is: in, They represent the echo delay error introduced by tropospheric propagation error, ionospheric propagation error, lunar track error, stop-and-go assumption error, and radar sampling position error, respectively. Indicates the echo delay under ideal conditions.

4. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation according to claim 3 is characterized in that: According to the atmospheric parameters and the Earth-Moon observation configuration files, a high-order polynomial is used to fit the time delay error of each orbit under long synthetic aperture time, and the variation range of the time delay error parameters of each orbit is estimated.

5. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation according to claim 1, characterized in that: The objective function is: τ estimate (j,k,l,n,v i )=τ ideal (j,k,l,n)+v i ·T(n) T(n)=[1nPRT(nPRT) 2 ...] T Among them, (j, k, l) represents the three-dimensional grid points, v is the variable to be optimized, and each vector v in v i The elements in represent the polynomial error parameters in the delay error of each track; The constraints are: v=[v 1 ;v 2 ...v N ]∈D v (4) Among them, n represents the corresponding azimuth time in each baseline, N a Indicates the total number of azimuth sampling points for each baseline, D v represents the variation range of the error parameter estimated according to the time-varying error model, PRT represents the radar azimuth sampling interval, τ ideal (j,k,l,n) represents the echo delay at the imaging grid point (j,k,l) ​​at azimuth time n under ideal conditions, s r i (τ estimate (j,k,l,n,v i ), n) represents the echo array after the range pulse compression, at the distance τ estimate (j,k,l,n,v i ) and echo data at time n.

6. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterized modeling and estimation according to claim 1, characterized in that: The step three uses a particle swarm optimization algorithm to solve the objective function established in the step two, and each particle is a multidimensional vector composed of polynomial parameters of the delay errors of each track.

7. The method for estimating and compensating the error of ground-based radar three-dimensional moon imaging based on error parameterization modeling and estimation according to claim 6 is characterized in that: The step three adopts an optimization strategy of first single-track search and then multi-track joint search to solve the objective function.

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