A Study on Range Cell Migration Correction in SAR Imagery and MATLAB Implementation of Algorithms

Abstract

Synthetic Aperture Radar(SAR) is an active microwave remote sensing technology that is used to create two-dimensional images of targets and the Earth surface through the use of radar [16]. SAR has many real time applications in different fields like as hydrology, geophysics, archeology etc. The term synthetic in the name comes from the concept of effectively creating a very long, narrow antenna by post-processing signal analysis rather than using a physical structure. This yields a much better resolution in the axis perpendicular to the radar beam(called the azimuth axis) effectively yielding images with quality normally only possible by using a much larger physical radar antenna. Goal of this thesis is to study and implementation of range doppler algorithm in MATLAB to extract out focused Single Look Complex (SLC) image that can be used for Automatic Target Recognition (ATR) and different techniques to correct range cell migration. The simulation results presented in this thesis are obtained from MATLAB environment where it is implemented a twodimension SAR target space as originally introduced by Brain Zaharris[22]. In this thesis, we have first implemented Range Doppler Algorithm(RDA) using synthetic data to get SLC image. Then RDA is used for the formation of SLC image from practical SAR data. In the simulation results, RDA has been implemented using SAR raw data that is collected from European Space Agency (ESA) via David Sandwell’s Data [13]. For focusing a moving target we need velocity compensation techniques. When the velocity of target is known by some other sources then range shifting methods will give good result for the focusing of moving target. However, this method will give good results only for a single moving target. For analysis of multiple moving target Keystone transformation (that is nothing but scaling of slow time parameter for uncoupling of fast frequency and slow time) will give better results. Keystone formatting [11] has the capability of compensating multiple targets range walk simultaneously without using any specific knowledge of the target motion, so it is widely used in the imaging of ground moving target[10] and dim target detection area [23].Therefore also, we have considered different relative velocity of targets with respect to SAR. Then range doppler matrix is formed and analyze the effect on moving target when velocity get increased.