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UBC Theses and Dissertations

Investigation of biases in Doppler centroid estimation algorithms Zhang, Tonghua

Abstract

Synthetic Aperture Radar (SAR) is a microwave imaging system capable of producing high-resolution imagery from data collected by a relatively small antenna. The Doppler centroid is an important parameter in the SAR signal processing. In principle, it is possible to calculate the Doppler centroid from orbit and attitude data. But the measurement uncertainties on these parameters will limit the accuracy of the estimation. Alternatively, the Doppler centroid can be estimated from the received data. In the past a few years, a number of Doppler centroid estimation algorithms have been developed. These algorithms can be categorized as one of two kinds. The first kind of algorithm utilizes the signal amplitude. The second kind of algorithm utilizes the phase of the received signal, such as the DLR algorithm, the MLCC and the MLBF algorithms. It is assumed that the estimation algorithms based on the signal phase can obtain more accurate estimates. The objective of this research is to examine and test the performance of the phased-based Doppler estimation algorithms with different scene contrasts, SNR levels and different squint angles, and examine the sensitivity of some phase-based Doppler estimation algorithms to radiometric discontinuities to find out how the radiometric discontinuities affect these estimation algorithms. First, the signal model is carefully examined. The effect of range sampling is discussed. The three candidate algorithms, the DLR, MLCC and MLBF, are introduced. Mathematical analysis of the ACCC angle and the contrast model are performed to obtain a insight of the operation of these algorithms. Experiments on simulated data with different scene contrast and SNR level are performed to compare the performance of these candidate algorithms. The MLCC algorithm works well with the ERS and J-ERS data, which normally have a low squint. However, it does not work reliably with the RADARSAT data. Since the RADARSAT data has a higher squint, simulations are performed to examine the effect of squint on the DLR, the MLCC and the MLBF algorithms. Radiometric discontinuity has significant effect on the estimate of the phasedbased algorithms. This thesis proposed a theory on the mechanism of how the radiometric discontinuity affects these algorithms in different ways. This thesis also proposed that, the MLBF is not affected by the radiometric discontinuity, the DLR algorithm is more sensitive to the azimuth discontinuity than the MLCC algorithm, whereas the M LCC algorithm is more sensitive to the range discontinuity than the DLR algorithm. These theories are proven by simulations and real data experiments.

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