Abstract
Abstract. Interferometric wide-swath mode of Sentinel-1, which is implemented by Terrain Observation by Progressive Scan (TOPS) technique, is the main mode of SAR data acquisition in this mission. It aims at global monitoring of large areas with enhanced revisit frequency of 6 days at the expense of reduced azimuth resolution, compared to classical ScanSAR mode. TOPS technique is equipped by steering the beam from backward to forward along the heading direction for each burst, in addition to the steering along the range direction, which is the only sweeping direction in standard ScanSAR mode. This leads to difficulty in measuring along-track displacement by applying the conventional method of multi-aperture interferometry (MAI), which exploits a double difference interferometry to estimate azimuth offset. There is a possibility to solve this issue by a technique called “Burst Overlap Interferometry” which focuses on the region of burst overlap. Taking advantage of large squint angle diversity of ~1° in burst overlapped area leads to improve the accuracy of ground motion measurement especially in along-track direction. We investigate the advantage of SAR Interferometry (InSAR), burst overlap interferometry and offset tracking to investigate coseismic deformation and coseismic-induced landslide related to 12 November 2017 Mw 7.3 Sarpol-e Zahab earthquake in Iran.
Highlights
With the frequent acquisition of satellite radar images, SAR Interferometry (InSAR) has become a widely used geodetic method of choice for Earth’s surface deformation monitoring
The semielliptical pattern pictured in ascending interferogram (Fig.1 a) indicates the ground moved towards the satellite over an area of about 40 by 60 km located in the southwest of the earthquake epicenter with a maximum LOS motion of ~ 1 meter
There are some local deformation spots exceeding 1 m, which are not seen in interferometry results due to large displacement gradient, mainly related to localized slope instability and rock falls triggered by the earthquake
Summary
With the frequent acquisition of satellite radar images, SAR Interferometry (InSAR) has become a widely used geodetic method of choice for Earth’s surface deformation monitoring. MAI technique is based on the split-beam InSAR processing In this method the sub-aperture processing is applied on the raw SAR data to produce forward and backward looking SLC pairs with different squint angles, i.e. an offset angle with respect to the zero Doppler direction. The variation in squint angles or equivalently the variation in Doppler centroid frequency is a key parameter to refine SD analysis, as its accuracy depends on a squint angular separation This technique is referred to as Burst Overlap Interferometry (Grandin et al, 2016). We use a combination of burst overlap interferometry and offset tracking to overcome the deficiency of offset tracking algorithm in dealing with wide TOPS images We complement this SAR analysis by applying Bayesian inversion for a dislocation model in an elastic half-space to infer source parameters and slip model of the earthquake (Okada, 1985). We use offset tracking displacement results in both along-track and across-track direction to evaluate displacement corresponding to a big landslide in the region that was triggered after this event
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