CN112630741B - Full-polarization synthetic aperture radar image target compensation PEOC method - Google Patents
Full-polarization synthetic aperture radar image target compensation PEOC method Download PDFInfo
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- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
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Abstract
The invention relates to the technical field of radar, and discloses a method for compensating a PEOC (target object offset) of a fully-polarized synthetic aperture radar image, which comprises the following steps: inputting full polarization data and expressing the data as a coherent matrix T; solving an orientation angle psi, an ellipticity angle tau and a phase angle theta; simultaneously carrying out orientation angle compensation, ellipticity angle compensation and phase angle compensation on the coherent matrix T by utilizing the target orientation angle psi, the ellipticity angle tau and the phase angle theta to obtain a compensated coherent matrixThereby rotating the object coherence matrix from the horizontal surface-based backscatter coordinate system to the object-based backscatter coordinate system. After compensation by PEOC, the number of negative power pixels occurring after decomposition can be effectively reduced.
Description
Technical Field
The invention relates to the technical field of radars, in particular to a PEOC (target-compensated object pass open) method for a fully-polarized synthetic aperture radar image.
Background
Polarized synthetic aperture radar (POLSAR) is an advanced earth observation synthetic aperture radar System (SAR). Compared with the traditional SAR, the polarized SAR greatly improves the acquisition capability of the scattering information of the ground target, and is one of the important directions of the development of the modern SAR. With the gradual and deep understanding of the theory of the polarized SAR and the continuous development of the SAR technology, the polarized SAR technology has been developed rapidly in the last decades. The polarization SAR is being widely and deeply applied in a plurality of fields such as land cover classification, surface feature parameter inversion, target identification, topographic mapping, city change monitoring, ocean monitoring and the like. One basic premise for the application of polarized SAR is to analyze the polarization characteristics of the target. Target polarization decomposition is an important and commonly used target polarization characteristic analysis technique. The model-based incoherent target polarization decomposition becomes an important branch of the target polarization decomposition due to simple operation and clear physical significance. In recent years, model-based incoherent target polarization decomposition has attracted extensive attention, attracts the attention of a large number of researchers, and has become a research hotspot and difficulty in the field of target polarization decomposition and polarized SAR.
In polarized synthetic aperture radar (POLSAR), the target exhibits a varying polarization on the polarized electromagnetic wave upon scattering, causing the elements of the scattering matrix of the target to couple with the horizontal-vertical polarization (HV) scattering coefficients in the conventional horizontal-horizontal polarization (HH), vertical-vertical polarization (VV) scattering coefficients.
Due to the fact that coupling exists between the same-polarization elements and the cross-polarization elements of the target scattering matrix, application problems of subsequent classification, change detection, decomposition and the like exist. The invention mainly solves the coupling of the same polarization and the cross polarization in the polarization scattering matrix, thereby being beneficial to the subsequent application. The invention mainly solves the coupling problem between the homopolarity component and the cross-polarization component in the polarimetric synthetic aperture radar image.
After the existing model-based incoherent target polarization decomposition method is decomposed, negative power always appears in pixels, which means that the target scattered echo power is negative and unreasonable. One of the reasons for the appearance of negative power pixels in model-based incoherent target polarization decomposition is that the target scattering matrix obtained by measurement is not truly built on the target-based backscatter coordinate system. By the PEOC method, the object coherent scattering matrix can be rotated to truly object-based backscatter coordinate coefficients.
Disclosure of Invention
The invention provides a target compensation PEOC method for a fully-polarized synthetic aperture radar image, which can rotate a scattering matrix from a backward coordinate system based on a horizontal ground to a backward scattering coordinate based on a target. Thereby solving the above-mentioned problems in the prior art.
The invention provides a PEOC (target Peroc) method for image target compensation of a fully-polarized synthetic aperture radar, which comprises the following steps of:
s1, inputting fully polarized data and expressing the data as a coherent matrix T:
s2, respectively solving the initial value psi of the orientation angle from the formula (2), the formula (3) and the formula (4) 0 Initial value of ellipticity angle τ 0 And an initial value of phase angle theta 0 Let I m 100、ψ m =ψ 0 、τ m =τ 0 And theta m =θ 0 ;
Wherein, tan -1 Is an arc tangent function of four quadrants, and Re and Im respectively represent the real part and the imaginary part of a complex number, and the factor in front of the formulaSo that the determined target orientation angle ψ, ellipticity angle τ, and phase angle θ are defined at [ - π/4, π/4];
S3, when the target orientation angleOval rate angle->Phase angle>The duration is over; carrying out target compensation on the coherent matrix T by using the target orientation angle psi, the ellipticity angle tau and the phase angle theta to obtain a compensated coherent matrix T;
S6, determining the target orientation angleOval rate angle->And phase angle>When the traversal is finished, the psi is output m 、τ m 、θ m And &>Otherwise, executing S3-S5 until the traversal is finished.
In the above S3, the specific steps of simultaneously performing the target compensation on the coherent matrix T by using the target orientation angle ψ, the ellipticity angle τ, and the phase angle θ to obtain the compensated coherent matrix are as follows:
s31, respectively carrying out target compensation on the coherent matrix by using the target orientation angle psi, the ellipticity angle tau and the phase angle theta as follows:
after the directional angle, the ellipticity angle and the phase angle of the coherent matrix are compensated respectively, corresponding elements are equal to 0, namely:
s32, simultaneously carrying out orientation angle compensation, ellipticity angle compensation and phase angle compensation on the coherent matrix to obtain a compensated coherent matrixWherein,
compared with the prior art, the invention has the beneficial effects that:
the invention proposes a PEOC compensation aiming at a coherent matrix, namely simultaneously performing orientation angle compensation (orientation compensation), ellipticity angle compensation (ellipticity angle compensation) and phase angle compensation (absolute angle compensation) from three elements of orientation angles, ellipticity angles and phase angles of a target which has polarization effect on electromagnetic waves and polarizes the electromagnetic waves, and rotates a scattering matrix from a backscattering coordinate system based on a horizontal surface to a backscattering coordinate system based on the target. Compared with the result of not performing the PEOC target compensation, the PEOC target compensation can effectively reduce the number of negative power pixels appearing after the polarization decomposition based on the model.
Drawings
Fig. 1 is a block diagram of a flow chart of a method for compensating for a PEOC in a fully-polarized synthetic aperture radar image target according to the present invention.
Fig. 2 is a specific flowchart of a method for compensating for a PEOC in a fully-polarized synthetic aperture radar image target according to the present invention.
Detailed Description
An embodiment of the present invention will be described in detail below with reference to fig. 1-2, but it should be understood that the scope of the present invention is not limited to the embodiment.
For the input fully polarized data, it can be expressed in the form of a coherence matrix:
the elements of the equation of the coherence matrix (1) are used to find the corresponding orientation angle ψ, ellipticity angle τ, and phase angle θ by the equations (2) - (4).
Wherein, tan -1 Is the arctangent function of the four quadrants. Re and Im respectively represent the real part and the imaginary part of the complex number. Due to the factor preceding the formulaSo that the determined target orientation angle ψ, ellipticity angle τ, and phase angle θ are defined at [ - π/4, π/4]。
The three angles are used to perform target compensation on the coherent matrix, and the compensation formulas are as follows (5) - (7).
After the directional angle, the ellipticity angle and the phase angle of the coherent matrix are compensated, the corresponding element is equal to 0, namely:
if the coherent matrix is simultaneously subjected to orientation angle compensation, ellipticity angle compensation and phase angle compensation, the method is the PEOC method of the invention, namely:
Or:
therefore, the flow of the PEOC target compensation is as in fig. 1.
The coherence matrix elements remain T after PEOC compensation 11 ,T 22 The magnitude relationship of (a).
2. PEOC target Compensation step
For PEOC compensation, the sum of the corresponding coherence matrix elements is minimized, i.e.: (14) formula (I).
Since the orientation angle ψ, the ellipticity angle τ, and the phase angle θ are solved and coupled to each other, the target compensation cannot be directly performed using the solved values of equations (2) to (4). To achieve the PEOC target compensation, the PEOC target compensation may be achieved using a traversal method.
Step 1: respectively solving the initial value psi of the orientation angle from (2), (3) and (4) 0 Initial value of ellipticity angle τ 0 And an initial phase angle value theta 0 And order I m =100,ψ m =ψ 0 、τ m =τ 0 And theta m =θ 0 ,
And 2, step: in thatAnd &>Traversing orientation angle ψ, ellipticity angle τ, and phase angle θ, respectively.
And step 3: compensating the fully polarized data by using the formula (12) by using the orientation angle psi, the ellipticity angle tau and the phase angle theta, and calculating
And 4, step 4: comparing I and I m If I < I m Then order psi m =ψ、τ m = τ and θ m =θ,And returning to the step 2 until the traversal is finished.
The invention proposes a PEOC compensation aiming at a coherent matrix, namely simultaneously performing orientation angle compensation (orientation compensation), ellipticity angle compensation (ellipticity angle compensation) and phase angle compensation (absolute angle compensation) from three elements of orientation angles, ellipticity angles and phase angles of a target which has polarization effect on electromagnetic waves and polarizes the electromagnetic waves, and rotates a scattering matrix from a backscattering coordinate system based on a horizontal surface to a backscattering coordinate system based on the target. Compared with the result of not performing the PEOC target compensation, the number of negative power pixels appearing after decomposition based on model polarization can be effectively reduced after the PEOC target compensation.
The above disclosure is only for a few specific embodiments of the present invention, however, the present invention is not limited to the above embodiments, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.
Claims (2)
1. A target compensation PEOC method for a fully-polarized synthetic aperture radar image comprises the following steps:
s1, inputting fully polarized data and expressing the data as a coherent matrix T:
s2, respectively solving the initial value psi of the orientation angle from the formula (2), the formula (3) and the formula (4) 0 Initial value of ellipticity angle τ 0 And an initial value of phase angle theta 0 Let I m =100、ψ m =ψ 0 、τ m =τ 0 And theta m =θ 0 ;
Wherein, tan -1 Is an arc tangent function of four quadrants, and Re and Im respectively represent the real part and the imaginary part of a complex number, and the factor in front of the formulaSo that the determined target orientation angle ψ, ellipticity angle τ, and phase angle θ are defined at [ - π/4, π/4];
S3, determining the target orientation angleEllipticity angle>Phase angleThe duration is over; performing target compensation on the coherence matrix T by using the target orientation angle psi, the ellipticity angle tau and the phase angle theta at the same time to obtain a compensated coherence matrix ^ based on>
2. The method for target compensation PEOC of fully-polarized synthetic aperture radar image according to claim 1, wherein the step S3 of simultaneously performing target compensation on the coherence matrix T by using the target orientation angle ψ, the ellipticity angle τ and the phase angle θ, and obtaining the compensated coherence matrix comprises the following steps:
s31, respectively carrying out target compensation on the coherent matrix by using the target orientation angle psi, the ellipticity angle tau and the phase angle theta as follows:
after the directional angle, the ellipticity angle and the phase angle of the coherent matrix are compensated respectively, corresponding elements are equal to 0, namely:
s32, simultaneously carrying out orientation angle compensation, ellipticity angle compensation and phase angle compensation on the coherent matrix to obtain a compensated coherent matrixWherein, U 3 (ψ,τ,θ)=U 3 (ψ)U 3 (τ)U 3 (θ), the coherence matrix after compensation @>The elements satisfy:
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