Analysis on radar imaging for target recognition from restricted scattering signals of target

Abstract

ISAR imaging is a target imaging method based on estimating the 2-D range-Doppler spectrum of a target, and is one of the most important technique for the area of non-cooperative target recognition. In order to recognize target accurately, improving image quality is very significant issue.

To improve target radar image quality, a lot of high-resolution techniques and image focusing techniques were reported. However, a fast target recognition technique is also important as well as both high image resolution technique and image focusing technique, and studies of the fast target recognition were insufficient. Thus, in this paper, an ISAR imaging method with short-term target observation was presented. However, using a target scattering signal of short-term observation encounters critical problem of resolution in cross-range due to lack of samples on the aspect angle and the limitation of target observing angle. To overcome cross-range resolution problem, first we modeled target scattering signal for short-term observing scenario, and then we obtained range profiles at each target aspect angle by conventional FFT method. After that, cross-range of each scatterers are extracted by ESPRIT-based method from each range bin. To improve computation efficiency, ESPRIT method is just perform to selected range bin which is discriminated to signal region by adopting threshold. A set of simulated and measured data of aircraft target is used to validate the proposed imaging method in this paper. By adopting the proposed method, required observation time of tar-get can be reduced to 12.5%.

Generally, ISAR image is attained from continuous target scattered signal, which is measured by tracking radar system with uniform time interval. In comparison with search radar system, tracking radar system costs more than search radar system, and it also has low penetration rate. Moreover, tracking radar system can detect and track the target only in the limited volume search area. However, by using the search radar system, volume search area can be extended since the search radar system adopts rotating antenna. Moreover, it can easily manage the multiple target due to the simplicity of separation of target signal. Thus, in this paper, an ISAR imaging method with search radar system was proposed. Due to the consistent movement of target, search radar system measured target scattered signal with non-uniform time interval. In order that, first we proposed target scattering signal considering the radar specification and target movement. The range profiles of target aspect angle were obtained by Fourier based method, and then the Doppler spectrums of each range bin were estimated by compressed sensing method.

In this paper, ISAR imaging methods for two types of restricted target scattering signals were introduced. The first one is, ISAR imaging method with short-term observing target scattered signal, and the second one is search radar ISAR imaging method. The performance of each proposed methods were shown with a set of data as an aircraft target.