An Efficient Maximum Likelihood Estimation Approach of Multi-Baseline SAR Interferometry for Refined Topographic Mapping in Mountainous Areas

Yuting Dong,Lu Zhang,Mingsheng Liao,Houjun Jiang

doi:10.3390/rs10030454

Abstract

For InSAR topographic mapping, multi-baseline InSAR height estimation is known to be an effective way to facilitate phase unwrapping by significantly increasing the ambiguity intervals and maintaining good height measurement sensitivity, especially in mountainous areas. In this paper, an efficient multi-baseline SAR interferometry approach based on maximum likelihood estimation is developed for refined topographic mapping in mountainous areas. In the algorithm, maximum likelihood (ML) height estimation is used to measure the topographic details and avoid the complicated phase unwrapping process. In order to be well-adapted to the mountainous terrain conditions, the prior height probability is re-defined to take the local terrain conditions and neighboring height constraint into consideration in the algorithm. In addition, three strategies are used to optimize the maximum likelihood height estimation process to obtain higher computational efficiency, so that this method is more suitable for spaceborne InSAR data. The strategies include substituting a rational function model into the complicated conversion process from candidate height to interferometric phase, discretizing the continuous height likelihood probability, and searching for the maximum likelihood height with a flexible step length. The experiment with simulated data is designed to verify the improvement of the ML height estimation accuracy with the re-defined prior height distribution. Then the optimized processing procedure is tested with the multi-baseline L-band ALOS/PALSAR data covering the Mount Tai area in China. The height accuracy of the generated multi-baseline InSAR DEM can meet both standards of American DTED-2 and Chinese national 1:50,000 DEM (mountain) Level 2.

Highlights

SAR interferometry (InSAR) is an effective tool for large-area topographic mapping due to its all-weather imaging and high sensitivity to terrain relief [1,2]
The InSAR height measurement accuracy is greatly influenced by the phase unwrapping accuracy and the length of normal baselines [3,4]
Longer normal baselines allow more accurate height estimation and generate higher frequency of the interferometric fringes, which increases the complexity of phase unwrapping

Summary

Introduction

SAR interferometry (InSAR) is an effective tool for large-area topographic mapping due to its all-weather imaging and high sensitivity to terrain relief [1,2]. To combine the advantages of large and short baselines in topographic mapping, a multi-baseline InSAR principle has been proposed to estimate terrain height by joint analysis of multiple interferometric pairs with diverse normal baselines [7,8]. Other multi-baseline estimation methods have been published to facilitate the phase unwrapping process by taking advantage of baseline diversity, such as the Least Square estimation method [5], the iterative multi-baseline method [12], the Chinese Remainder Theorem (CRT) method [13,14], and so on These multi-baseline phase unwrapping methods can significantly increase the ambiguity intervals of interferometric phases and keep the topographic details as well; these methods still have to solve the phase unwrapping problem correctly

Results

Discussion

Conclusion