CN-122017857-A - Strabismus synthetic aperture sonar imaging method based on dynamic oblique space variant model

CN122017857ACN 122017857 ACN122017857 ACN 122017857ACN-122017857-A

Abstract

The invention discloses a strabismus synthetic aperture sonar imaging method based on a dynamic oblique space variant model, which relates to the technical field of synthetic aperture sonar imaging and comprises the steps of constructing a dynamic oblique space model; the method comprises the steps of inputting transformed data into a dynamic oblique transformation model to obtain residual space-variant distance bending quantity, compensating the space-variant distance bending quantity by using a first filter, expanding azimuth time offset into azimuth frequency modulation factors according to the dynamic oblique transformation model, designing a second filter by adopting an improved expanded nonlinear frequency modulation scaling algorithm based on the azimuth frequency modulation factors and the azimuth time offset, filtering the corrected data by using the second filter, carrying out Fourier transformation on the filtered data, compressing the transformed data by using a third filter, and carrying out inverse Fourier transformation to obtain a focused synthetic aperture sonar image. The invention can improve the imaging performance and stability of the imaging algorithm in the environment of low signal-to-noise ratio and strong multi-path interference.

Inventors

LUAN YUZHEN
LU SENXIANG

Assignees

东北大学

Dates

Publication Date: 20260512
Application Date: 20260410

Claims (9)

1. A strabismus synthetic aperture sonar imaging method based on a dynamic oblique space variant model is characterized by comprising the following steps: Acquiring original echo data, wherein the original echo data is acquired through strabismus synthetic aperture sonar; Constructing a dynamic inclined distance model, wherein the dynamic inclined distance model is obtained based on the improvement of a round model and is used for correlating the instantaneous inclined distance of a target point with the inclined distance of a reference point; Preprocessing the original echo data and carrying out Keystone transformation, determining residual space-variant distance bending quantity according to the dynamic oblique distance model, and compensating the residual space-variant distance bending quantity by using a first filter constructed based on an improved nonlinear frequency modulation scaling algorithm to obtain corrected data; According to the dynamic oblique distance model, expanding the azimuth time offset into an azimuth frequency modulation factor; Based on the azimuth frequency modulation factor and the azimuth time offset, adopting an improved extended nonlinear frequency modulation scaling algorithm to design a second filter, and filtering corrected data by using the second filter; and carrying out Fourier transform on the filtered data, compressing the transformed data by using a third filter, and carrying out inverse Fourier transform on the compressed data to obtain a focused synthetic aperture sonar image.
2. The strabismus synthetic aperture sonar imaging method based on the dynamic oblique space variant model according to claim 1, wherein the calculation formula of the dynamic oblique space variant model is as follows: Wherein, the For the instantaneous skew of the target point, As the slant distance of the reference point, For the speed of movement of the sonar platform, In order to achieve a squint angle, Is the azimuth time offset of the target point relative to the reference point.
3. The strabismus synthetic aperture sonar imaging method based on the dynamic range space variant model according to claim 1, wherein the perturbation function of the first filter is: Wherein, the As a function of the perturbation of the first filter, In order to be a distance frequency, For the time after the Keystone transformation, In units of imaginary numbers, Is the coefficient of the third order disturbance, For the four perturbation coefficients, Is the speed of sound.
4. The strabismus synthetic aperture sonar imaging method based on the dynamic oblique space variant model according to claim 1, wherein the calculation formula of the azimuth frequency modulation factor is as follows: ; Wherein, the For the azimuth frequency modulation factor, For the azimuthal frequency modulation rate of the reference point, For the one-time expansion coefficient, the first expansion coefficient, As the amount of azimuth time offset, Is the secondary expansion coefficient.
5. The strabismus synthetic aperture sonar imaging method based on the dynamic range space variant model according to claim 1, wherein the expression of the second filter is: Wherein, the As a phase correction function of the second filter, As the azimuth frequency of the light beam, As the amount of azimuth time offset, In units of imaginary numbers, For the azimuth frequency modulation factor, The coefficients are obtained by three times of coefficients, Is the space-variant coefficient of the cubic phase, And is a coefficient of four times.
6. The strabismus synthetic aperture sonar imaging method based on the dynamic range space-variant model according to claim 5, wherein the three-order coefficient, the four-order coefficient and the three-order phase space-variant coefficient are obtained by solving a phase matching equation set.
7. The strabismus synthetic aperture sonar imaging method based on the dynamic range space variant model according to claim 6, wherein the formula of the phase matching equation set is: Wherein, the The coefficients are obtained by three times of coefficients, For the coefficient of four times, Is the space-variant coefficient of the cubic phase, For the maximum azimuth time offset of the scene edge, For the one-time expansion coefficient, the first expansion coefficient, Is the coefficient of the secondary expansion and is used for the secondary expansion, Is the azimuth frequency modulation rate of the reference point.
8. The strabismus synthetic aperture sonar imaging method based on the dynamic range space variant model according to claim 1, wherein the third filter is an azimuth matched filter, and the expression of the third filter is: Wherein, the In units of imaginary numbers, For the output of the third filter, As the azimuth frequency of the light beam, Is the azimuth frequency modulation rate of the reference point.
9. The strabismus synthetic aperture sonar imaging method based on the dynamic oblique space variant model according to claim 1, wherein the method further comprises analyzing and evaluating azimuth secondary phase errors, and a calculation formula of the secondary phase errors is as follows: Wherein, the Is the error of the secondary phase and is used for the method, For the azimuth frequency modulation factor, For the azimuthal frequency modulation rate of the reference point, For the one-time expansion coefficient, the first expansion coefficient, As the amount of azimuth time offset, Is the coefficient of the secondary expansion and is used for the secondary expansion, Is the synthetic aperture time.

Description

Strabismus synthetic aperture sonar imaging method based on dynamic oblique space variant model Technical Field The invention relates to the technical field of underwater acoustic signal processing and synthetic aperture sonar imaging, in particular to a strabismus synthetic aperture sonar imaging method based on a dynamic oblique space variant model. Background Synthetic aperture sonar (SYNTHETIC APERTURE SONAR, SAS) is a high resolution underwater imaging device based on synthetic aperture technology and signal processing technology. The high-definition imaging of submarine topography, buried targets and the like can be realized by forming a virtual long aperture through the motion of the sonar platform and combining a pulse compression technology. SAS systems are mainly divided into two working modes of a front side view mode and an oblique view mode according to different beam pointing angles. The strabismus mode has higher observation flexibility, can realize imaging outside an area, and shows remarkable advantages in the fields of military reconnaissance, submarine resource exploration and the like. In particular, for the detection of complex seafloor terrain and concealed objects, strabismus SAS systems can provide more comprehensive viewing perspectives and richer object information. In the technical field of strabismus SAS imaging, a nonlinear frequency modulation scaling (NLCS) algorithm and an Expansion (ENLCS) algorithm thereof are high-precision imaging methods which are mature at present. These algorithms theoretically enable high resolution imaging under strabismus conditions by building accurate geometric models and performing phase compensation. However, in an actual marine environment, echo signals received by a strabismus SAS system are affected by various adverse factors, namely, firstly, a large strabismus angle can cause the invariance of range migration to be aggravated, secondly, point targets at different azimuth positions have different Doppler tuning frequencies, namely, the problem of azimuth tuning frequency space-variant exists, and furthermore, the conventional fixed geometric model is difficult to accurately describe the range variation under a wide mapping band. When the conventional ENLCS algorithm processes strabismus SAS data, the Taylor expansion approximation point target instantaneous skew is generally adopted, and the skew relation of different point targets in the same distance unit is described by depending on a fixed geometric model such as a simple circle model and the like. Under the conditions of higher moving speed of the sonar platform, larger squint angle or wider swath, the model approximation error can be obviously increased, so that the focusing performance of azimuth (especially the edge area of a scene) is reduced, the secondary phase error exceeds the allowable range, and finally the imaging quality is influenced. Disclosure of Invention According to the proposed strabismus synthetic aperture sonar imaging algorithm, when the large strabismus visual angle and high-speed motion platform data are processed, the problem of defocusing of the image edge is caused by insufficient precision of a geometric model, and the strabismus synthetic aperture sonar imaging method based on a dynamic strabismus space-variant model is provided. The method mainly builds a dynamic slope distance model containing a secondary correction term, remarkably improves the accuracy of slope distance calculation, effectively compensates azimuth space-variant errors through space-variant distance migration correction and azimuth frequency modulation factor expansion balance, finally realizes uniform focusing of the whole scene, strictly controls the secondary phase errors within an imaging requirement threshold, and solves the defocusing problem of the scene edge in the traditional method. The invention adopts the following technical means: A strabismus synthetic aperture sonar imaging method based on a dynamic oblique space variant model comprises the following steps: Acquiring original echo data, wherein the original echo data is acquired through strabismus synthetic aperture sonar; Constructing a dynamic inclined distance model, wherein the dynamic inclined distance model is obtained based on the improvement of a round model and is used for correlating the instantaneous inclined distance of a target point with the inclined distance of a reference point; Preprocessing the original echo data and carrying out Keystone transformation, determining residual space-variant distance bending quantity according to the dynamic oblique distance model, and compensating the residual space-variant distance bending quantity by using a first filter constructed based on an improved nonlinear frequency modulation scaling algorithm to obtain corrected data; According to the dynamic oblique distance model, expanding the azimuth time offset into an azimuth frequency modulation factor; Based on the azimuth