Radiometric image quality improvement of scansar data
Creators: name: Vigneron, Catherine M.
Publisher: name: University of British Columbia
Year: 2009

description: Remotely-sensed synthetic aperture radar (SAR) image data are of fundamental importance for the detection and monitoring of characteristics of the Earth's surface such as geophysical parameters, ocean current patterns, and agricultural crop features. In 1998, the European Space Agency will launch the ENVISAT-1 satellite which will carry an Advanced Synthetic Aperture Radar (ASAR) system capable of imaging large portions of the Earth's surface using a Scanning Synthetic Aperture Radar (ScanSAR) mode of operation. However, these images will be of little value to the Earth observation community if the quality of processed images is degraded to such an extent that significant terrain features cannot be identified. The objective of this thesis was to investigate techniques for maximizing the radiometric image quality of remote sensing images processed using ENVISAT ScanSAR satellite data. These techniques aim to reduce the output radiometric scalloping (which appears in an image as repeated 'bands' of intensity variation) in azimuth to a level below which it is visibly undetectable (0.2 dB). To accomplish this objective, selected methods for antenna pattern correction and Doppler centroid estimation were evaluated and compared in this context. The investigation and results of the comparative analysis of the methods are summarized below. Ideal-scenario simulations were carried out for the evaluation of the Inverse Beam Pattern Method and the Constant SNR Method for antenna pattern correction, for up to 4 looks per aperture. Both the Inverse Beam Pattern Method (IBP) and the Constant SNR Method (CSNR) for antenna pattern correction were found to be less sensitive to the effects of Doppler centroid estimation errors for an increasing number of looks per aperture. In addition, the IBP method consistently showed a maximization of the equivalent number of looks over azimuth. Conversely, the CSNR functions derived to minimize the residual scalloping resulted in an equivalent number of looks which was not maximized over azimuth. It is possible that the amount of scalloping was increased using the CSNR method for this reason in practice, when compared to the simulation results for the 2 look implementation. As a result, there appeared to be little distinction between the practical performance of scalloping reduction of the CSNR and IBP methods for the 2 look implementation. Selected Spectral Distribution Analysis and Phase Increment Methods for Doppler centroid estimation were implemented and evaluated using ERS-1 SAR data to simulate the ENVISAT ScanSAR case. The performance of each of the selected methods for Doppler centroid estimation was found to be sensitive to scene contrast and to the presence of land-sea boundaries in the scene. However, the Doppler centroid estimations derived using the Look Power Balancing Method were found to be more accurate than those measured using other methods over image areas of high scene contrast and for areas containing land-water boundaries. This is largely due to the fact that, contrary to the other methods tested, the accuracy of the Look Power Balancing Method does not rely on the validity of assumptions related to scene reflectivity and/or the distribution of individual scatterers. In addition, the performance of the Look Power Balancing Method for Doppler centroid estimation was found to be sensitive to antenna pattern modelling.