Adaptive Local Polynomial Fourier Transform in ISAR
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Adaptive Local Polynomial Fourier Transform in ISAR Igor Djurovi´c,1 Thayananthan Thayaparan,2 and Ljubiˇsa Stankovi´c1 1 Electrical
Engineering Department, University of Montenegro, 81000 Podgorica, Serbia and Montenegro of National Defence, Defence R & D Canada - Ottawa, 3701 Carling Avenue, Ottawa, ON, Canada K1A 0Z4
2 Department
Received 23 May 2005; Revised 14 November 2005; Accepted 15 November 2005 The adaptive local polynomial Fourier transform is employed for improvement of the ISAR images in complex reflector geometry cases, as well as in cases of fast maneuvering targets. It has been shown that this simple technique can produce significantly improved results with a relatively modest calculation burden. Two forms of the adaptive LPFT are proposed. Adaptive parameter in the first form is calculated for each radar chirp. Additional refinement is performed by using information from the adjacent chirps. The second technique is based on determination of the adaptive parameter for different parts of the radar image. Numerical analysis demonstrates accuracy of the proposed techniques. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
The inverse synthetic aperture radar (ISAR) has attracted wide interest within scientific and military community. Some ISAR applications are already well known and studied. However, many important issues remain to be addressed. For example, suitable enhancement technique for the fast maneuvering radar targets or targets with fast moving parts is not yet known. Also, standard approaches based on the Fourier transform (FT) fail to resolve influence of close reflectors. There are several techniques for improvement of the ISAR radar image in the case of fast maneuvering targets or in the case of objects with complex reflector geometry. Here we mention only two groups of such enhancement techniques as follows: (i) techniques that adopt transform parameters for assumed parametric target motion model [1], (ii) techniques where reflection signal components are parametrized, while the signal components caused by reflectors are estimated by using some of well developed parametric spectral estimation tools [2, 3]. Both of these techniques have some advantages, but also some drawbacks for specific applications. The first group of techniques is strongly based on radar target geometry with assumed motion model. These techniques could become inaccurate in the case of a changing motion model. The second group of techniques is tested on simulated examples.
However, its application in real scenarios, where signal components are caused by numerous scatterers, could be very difficult. Namely, there are no appropriate methods for parameters estimation of signals with a very large number of components. In this paper we propose a modification of the first group of research techniques. The adaptive local polynomial Fourier transform (LPFT) is used. Adaptive coefficients are calculated for each considered chirp in the radar signal mixture. It is important to note that the
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