EDGE DETECTION IN POLARIMETRIC SYNTHETIC APERTUE RADAR IMAGES

Abstract

Polarimetric synthetic aperture radar (PolSAR) is an active imaging radar system that remotely senses the target/area illuminated by microwaves which is employed in varied range of applications from agriculture, forest, urban and military. The ability of the system to be operated in all weather and all time due to it’s operation in a microwave region in the frequency spectrum has made this system a popular one. PolSAR radar gets the description about the target and it’s physical properties using polarization property of the electromagnetic (EM) waves. A fully polarimetric radar simultaneously transmits and receive microwave pulses with two different orthogonal polarizations. It measures the back scatter coefficients at two orthogonal polarizations, and forms a image of the target that is being observed. Fully polarimetric measurements thus constitute a complete description of the scattering characteristics of the target in a single resolution cell. In radar polarimetry, the complex scattering coefficients measured at different polarizations are used to characterize the target. Edge detection in PolSAR images is an important image processing step employed for processing the PolSAR data. It entails finding the change in intensity level in an image so as to register it as an edge. This is a basic and necessary processing step for further ”segmentation, registration, and identification” of the features in PolSAR data [1]. An edge detector finds discontinuity or change in sudden intensity level in an image, this detected edge may further be utilized for processing the image to generate various segments based on some defined characteristics or to map the images to certain physical parameters. This thesis unfolds in two major section. Firstly it describes various edge detection methods that are currently being used in field of PolSAR imagery, with their suitability and compatibility in application to PolSAR data. It also gives on account of detail into necessity of contrast enhancement in the process of edge detection. There after a novel technique is introduced comprising of an algorithm that efficiently enhances the PolSAR image contrast by entropy v Abstract maximization and robustly detects the edges. Further an application of edge detection in order to detects the road and boundaries in a rural area is discussed with data obtained from various airborne and space borne radars.