SAR azimuth ambiguity suppression method based on improved ideal filter

Abstract

The invention provides an SAR azimuth ambiguity suppression method based on improved ideal filter, which is suitable for a point target and a non-point target, is independent of a specific signal mode, and meanwhile, is suitable for the realization of a rapid engineering of azimuth ambiguity suppression in a large area scene, and dispenses with processing in sections. The method comprises the following steps: step one, generating a low ambiguity image, utilizing signals which are relatively low in ambiguity energy and within Doppler frequency range to generate a reference image with low resolution and low ambiguity energy, and in registration with finished amplitude of an original image to-be-processed; step two, generating an ambiguity signal image, utilizing the ideal filter algorithm to finish 0-degree and 180-degree filtering, and subtracting results to obtain a modulus so as to obtain the ambiguity signal image; step three, generating an ambiguity indicating image; and step four, generating an ambiguity suppression result image.

Description

Technical field [0001] The invention is a SAR azimuth ambiguity suppression method based on an improved ideal filter, which relates to the field of synthetic aperture radar (SAR) signal processing, in particular to the field of synthetic aperture radar image azimuth ambiguity suppression processing. Background technique [0002] SAR obtains high azimuth resolution through the relative movement between the sensor and the target. Using the Doppler effect, the relative movement between the radar and the target generates a Doppler frequency in the direction of the echo signal. However, since SAR is equivalent to sampling with PRF as the sampling frequency in the azimuth direction, the echo with higher Doppler frequency generated outside the beam width of the main lobe of the antenna is under-sampled and received, forming an azimuth ambiguity signal, and then It becomes a "defocused ghost target" in the two-dimensional compressed SAR image. Severe azimuth will affect the interpretat...

AI Technical Summary

Problems solved by technology

However, since the SAR is equivalent to sampling with the PRF as the sampling frequency in the azimuth direction, the echo with a higher Doppler frequency generated outside the beam width of the main lobe of the antenna is received by under-sampling to form an azimuth ambiguous signal, and then Becoming a "defocused ghost target" in a 2D compressed SAR image

Severe azimuth ambiguity will affect the interpretation and interpretation of SAR images, especially in SAR marine military monitoring, the backscatter coefficient of the sea surface is relatively small, and the backscatter coefficient of coastal land, especially ships at sea, is relatively large. The azimuth blurred image of a strong scattering target will interfere with the real target and become a false target on the SAR image of the sea surface, which often has a serious impact on the interpretation of the SAR image

The problem of azimuth ambiguity in SAR images can generally be alleviated by optimizing the design of antennas. However, since the problem of azimuth ambiguity in SAR images is inherent in the SAR imaging mechanism, especially for spaceborne SAR, with the continuous improvement of spatial resolution, The difficulty of system optimization design has increased significantly, and azimuth ambiguity has gradually become one of the important issues affecting the image quality and application of spaceborne SAR

[0012] 1) The suppression effect on non-point targets is not obvious

Since in the ideal point target model, the scattering characteristics of the target do not change with the change of the irradiation angle of the SAR sensor to the target, but the scattering characteristics of the actual target are difficult to be accurately described by such an ideal model. Therefore, as the target deviates from the ideal point target increase, the greater the difference between the blurred image constructed by this scheme and the real blurred image, coupled with the influence of noise and signal saturation, the effect of suppressing the azimuth blur of non-point targets based on the ideal filter algorithm is not good

[0013] 2) A large number of blocks are required for large area scenes

[0014] In short, there are problems in the existing technical solutions in terms of the scattering characteristics of the actual scene and the applicability to the actual engineering realization

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