DOI: 10.4211/hs.d03e53c0d3eb4c72ad43edc0b309755a
title: Time Series of InSAR-Measured Seasonal Surface Deformation Induced by the West African Monsoon in Sudanian West Africa

description: This dataset consists of InSAR-measured line-of-sight surface deformation over the Ara watershed (located in northern Benin) for two dry seasons (November 2015-June 2016 and November 2016-June 2017).  Thirty-six single look complex (SLC) images acquired by the Sentinel 1 mission were obtained from the Alaska Satellite Facility (ASF) Distributed Active Archive Centers (DAAC; http://www.asf.alaska.edu/).  12-, 24-, and 36-day interferograms were generated using the open source (GNU General Public License) Generic Mapping Tools 5 Synthetic Aperture Radar (GMT5SAR) processing system (Sandwell et al 2016, Massonnet and Feigl 1998).  GMT5SAR geometrically aligns Sentinel TOPSAR images to a single master image with centimeter accuracy, maps topography into phase, and forms a stack of complex interferograms (Sandwell et al 2016).  The Generic Mapping Tools- (GMT-) (Wessel et al 2013) based GMT5SAR postprocesser filters the interferogram and generates phase, coherence, and phase gradient products.  GMT5SAR unwraps the interferograms using the well-known snaphu algorithm (Chen and Zebker 2000).  Filter and decimation parameters for the inSAR processing were chosen to produce relatively high resolution interferograms, considering the computational cost of phase unwrapping.  Lighter filtering and decimation improves interferogram resolution, but increases the computational time for phase unwrapping.  Pixels were decimated by a factor of 8 in the range and 2 in the azimuth directions, generating interferograms with a pixel size of approximately 18.4 x 28.2 meters (range x azimuth).  A 100 meter Gaussian filter was selected for the Ara study area.  Enhances spectral diversity was used to reduce phase mismatch at the burst boundary (Sandwell et al 2016).  The new small baseline subset(NSBAS) technique (Doin et al 2011) was used was used to generate a time series analysis of deformation across the study area.  The NSBAS algorithm was applied using the Generic InSAR Analysis Toolbox (GIAnT; Agram et al 2012, 2013).  The GIAnT tool box stacked the geometrically-aligned phase-unwrapped interferograms, estimated and applied corrections for residual long‐wavelength errors due to imprecise orbits, and estimated line-of-sight displacements using the NSBAS technique.

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