Abstract
We aim to address two primary issues using the multitemporal (MT) spaceborne SAR observations and InSAR technique to monitor slope stability in rugged terrains. One is how to maximize the observation and application effectiveness based on the geometric distortion in an area of interest for determining appropriate ascending- and descending-orbit SAR observations. The other is how to optimize the selection of ground control points (GCPs) to correct orbital phase errors and reference in deriving valid ground surface displacements in the SBAS InSAR analysis. Four criteria were proposed to identify valid GCPs efficiently and effectively. The 2017 Xinmo landslide event, China, was showcased. The tear-away zone was 100% and ∼50% distorted when imaged by ascending- and descending-orbit Sentinel-1A/B SAR sensors. The descending SAR datasets were preferred. Then, we identified four spatially dispersed GCP clusters with the selection criteria using the SBAS InSAR technique and 45 descending-orbit MT SAR datasets. One GCP per cluster was chosen. With the four GCPs and SBAS analysis, we successfully detected the stable status in the landslide-free area and the prelandslide acceleration movement within the tear-away zone. Valid InSAR-derived results have been obtained. In turn, the GCP selection criteria have been validated, and the two issues resolved.
Highlights
THE spaceborne synthetic aperture radar (SAR) uses the side-looking imaging geometry to observe an area of interest (AOI) in Earth observation
Geometric distortions can occur when a polar-orbit SAR images the area of interest (AOI), and the degree of distortions differs for ascending- or descending-orbit SAR observations
As artificial targets are scarce and difficult to conduct fieldwork in remote mountainous areas, the ground control points (GCPs) is primarily selected by analyzing the SAR and interferometric SAR (InSAR) datasets
Summary
THE spaceborne synthetic aperture radar (SAR) uses the side-looking imaging geometry to observe an area of interest (AOI) in Earth observation. When the side-looking SAR images rugged terrain, geometric distortion [16], i.e., foreshortening, layover, or shadow, can occur along the line-of-sight (LOS) direction. The distortion affects the effectiveness of using the multi-temporal (MT) SAR observations and InSAR analysis to evaluate the surface. Debris of a landslide event in mountainous areas flows along slope downwards. The tear-away zone of a landslide can be any location along a hill. The zone’s location determines the debris flow direction and path. A SAR observable area in rugged terrain is determined by the interplay of the SAR look angle and the slope and aspect angles of the hill. The quantitative analysis of the interplay is crucial, allowing one to maximize the MT SAR observations’ chance to observe the tear-away zone. A better assessment of the debris flow and path is obtained
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