New approaches to topography estimation using interferometric SAR images.

摘要

Topographic information is vital for a wide range of environmental sciences, such as geology, hydrology, and global climate change research. Interferometric synthetic aperture radar (INSAR) presents a new technology for performing high resolution topographic mapping. Compared with other elevation mapping technologies, INSAR has the advantages of all-weather capability and high resolution.; This thesis investigates several issues in the elevation mapping process for interferometric SAR. Among the factors critical to mapping accuracy are registration of the interfering SAR images and phase unwrapping. A novel registration algorithm is developed which determines the registration parameters through an optimization process. A new measure of merit is proposed to evaluate the registration result during the optimization. The phase unwrapping problem is solved through fringe line detection that prevents error propagation and produces negligible local errors. An edge segment linking algorithm and a curve fitting algorithm are developed, and their performances compared. To better understand the relationship between phase difference and surface elevation, a geometric model is derived. The model shows that the phase difference consists of contributions from a flat surface and from terrain elevation fluctuations with respect to the flat surface. Further, an iterative algorithm is developed to solve for the ground range position and the elevation of each surface point simultaneously. In addition, this research studies the evaluation of SAR elevation mapping accuracy. The accuracy is determined by comparing SAR elevation estimates with a digital elevation map (DEM) of the same area. A method of registering interferometric SAR data with a DEM is developed using a phase difference image simulated from the DEM according to the SAR imaging geometry. The layover effect and its correction are also explored.; Test results of the algorithms are shown using actual interferometric SEASAT SAR images over large relief terrain near Yellowstone National Park with a short baseline, and over relatively flat terrain in the Death Valley of California with a long baseline. Comparison between the elevation estimated from INSAR data with a USGS digital elevation map obtained using stereo photogrammetry is made for the first time, and results show a better agreement than other SAR elevation mapping techniques.