A Novel Method for Layover Detection in Mountainous Areas with SAR Images

It is well known that there are geometric distortions in synthetic aperture radar (SAR) images when the terrain undulates. Layover is the most common one, which brings challenges to the application of SAR remote sensing. This study proposes a novel detection method that is mainly aimed at the layover caused by mountains and can be performed with only medium-resolution SAR images and no other auxiliary data. The detection includes the following four stages: initial processing, difference image calculation and rough and fine layover detection. Initial processing mainly obtains the potential layover areas, which are mixed with the built-up areas after classification. Additionally, according to the analysis of the backscatter coefficient (BC) of various ground objects with different polarization images, the layover areas are detected step-by-step from the mixed areas, in which the region-based FCM segmentation algorithm and spatial relationship criteria are used. Taking the Danjiangkou Reservoir area as the study area, the relevant experiments with Sentinel-1A SAR images were conducted. The quantitative analysis of detection results adopted the figure of merit (FoM), and the highest accuracy was up to 87.6% of one selected validation region. Experiments in the South Taihang area also showed the satisfactory effect of layover detection, and the values of FoM were all above 85%. These results show that the proposed method can do well in the layover detection caused by mountains. Its simplicity and effectiveness are helpful in removing the influence of layover on SAR image applications to a certain extent and improving the development of SAR remote sensing technology.

A REVIEW OF SURGE-TYPE GLACIERS

The study of glacier surges is meaningful for the understanding of glacier dynamics and the mechanisms of surge-type glaciers. Here, we briefly introduce the distribution of surge-type glaciers and the reason of their tendency to cluster within particular regions. Then we make a review of optical and SAR remote sensing methods for the spaceborne measurement of the surface velocity about surge-type glaciers and show the details of characteristics of Surging Glaciers including the acceleration and deceleration of the velocity of the glacier surface, the terminus may move forward a few kilometers in just a few months, then we give a specific example of surge-type glacier, Sortebræ. Finally, we summarize the existing mechanism of the glaciers surging.