TY - JOUR

T1 - Ground Deformations around the Toktogul Reservoir, Kyrgyzstan, from Envisat ASAR and Sentinel-1 Data—A Case Study about the Impact of Atmospheric Corrections on InSAR Time Series

AU - Neelmeijer, Julia

AU - Schöne, Tilo

AU - Dill, Robert

AU - Klemann, Volker

AU - Motagh, Mahdi

N1 - Funding information: Acknowledgments: The Sentinel-1 and Envisat data used for this study are provided by the European Space Agency/Copernicus. The SRTM DEM data were derived from the Consortium for Spatial Information of the Consultative Group for International Agricultural Research (CGIAR–CSI). The Landsat data were obtained from the U.S. Geological Survey. We thank Deutscher Wetterdienst, Offenbach, Germany, and the European Centre for Medium Range Weather Forecast, Reading, U.K., for providing data from ECMWF’s operational forecast model, the ERA-5 reanalysis and the ERA-I reanalysis. This work was funded by the Initiative and Networking Fund of the Helmholtz Association in the framework of the Helmholtz Alliance “Remote Sensing and Earth System Dynamics” (EDA) and by the CAWa project (Contract No. AA7090002), funded by the German Federal Foreign Office. The study contributes to the “Advanced Earth System Modelling Capacity” (ESM) project of the Helmholtz Association of German Research Centres. We also appreciate the valuable comments and constructive suggestions of four anonymous reviewers, which greatly helped us to improve our manuscript.

PY - 2018/3/15

Y1 - 2018/3/15

N2 - We present ground deformations in response to water level variations at the Toktogul Reservoir, located in Kyrgyzstan, Central Asia. Ground deformations were measured by Envisat Advanced Synthetic Aperture Radar (ASAR) and Sentinel-1 Differential Interferometric Synthetic Aperture Radar (DInSAR) imagery covering the time periods 2004-2009 and 2014-2016, respectively. The net reservoir water level, as measured by satellite radar altimetry, decreased approximately 60m (~13.5km3) from 2004-2009, whereas, for 2014-2016, the net water level increased by approximately 51m (~11.2km3). The individual Small BAseline Subset (SBAS) interferograms were heavily influenced by atmospheric effects that needed to be minimized prior to the time-series analysis. We tested several approaches including corrections based on global numerical weather model data, such as the European Centre for Medium-RangeWeather Forecasts (ECMWF) operational forecast data, the ERA-5 reanalysis, and the ERA-Interim reanalysis, as well as phase-based methods, such as calculating a simple linear dependency on the elevation or the more sophisticated power-law approach. Our findings suggest that, for the high-mountain Toktogul area, the power-law correction performs the best. Envisat descending time series for the period of water recession reveal mean line-of-sight (LOS) uplift rates of 7.8 mm/year on the northern shore of the Toktogul Reservoir close to the Toktogul city area. For the same area, Sentinel-1 ascending and descending time series consistently show a subsidence behaviour due to the replenishing of the water reservoir, which includes intra-annual LOS variations on the order of 30mm. A decomposition of the LOS deformation rates of both Sentinel-1 orbits revealed mean vertical subsidence rates of 25 mm/year for the common time period of March 2015-November 2016, which is in very good agreement with the results derived from elastic modelling based on the TEA12 Earth model.

AB - We present ground deformations in response to water level variations at the Toktogul Reservoir, located in Kyrgyzstan, Central Asia. Ground deformations were measured by Envisat Advanced Synthetic Aperture Radar (ASAR) and Sentinel-1 Differential Interferometric Synthetic Aperture Radar (DInSAR) imagery covering the time periods 2004-2009 and 2014-2016, respectively. The net reservoir water level, as measured by satellite radar altimetry, decreased approximately 60m (~13.5km3) from 2004-2009, whereas, for 2014-2016, the net water level increased by approximately 51m (~11.2km3). The individual Small BAseline Subset (SBAS) interferograms were heavily influenced by atmospheric effects that needed to be minimized prior to the time-series analysis. We tested several approaches including corrections based on global numerical weather model data, such as the European Centre for Medium-RangeWeather Forecasts (ECMWF) operational forecast data, the ERA-5 reanalysis, and the ERA-Interim reanalysis, as well as phase-based methods, such as calculating a simple linear dependency on the elevation or the more sophisticated power-law approach. Our findings suggest that, for the high-mountain Toktogul area, the power-law correction performs the best. Envisat descending time series for the period of water recession reveal mean line-of-sight (LOS) uplift rates of 7.8 mm/year on the northern shore of the Toktogul Reservoir close to the Toktogul city area. For the same area, Sentinel-1 ascending and descending time series consistently show a subsidence behaviour due to the replenishing of the water reservoir, which includes intra-annual LOS variations on the order of 30mm. A decomposition of the LOS deformation rates of both Sentinel-1 orbits revealed mean vertical subsidence rates of 25 mm/year for the common time period of March 2015-November 2016, which is in very good agreement with the results derived from elastic modelling based on the TEA12 Earth model.

KW - Atmosphere correction

KW - DInSAR

KW - Elastic modelling

KW - Ground deformation

KW - Reservoir monitoring

KW - SBAS

KW - Toktogul reservoir

UR - http://www.scopus.com/inward/record.url?scp=85044217084&partnerID=8YFLogxK

U2 - 10.3390/rs10030462

DO - 10.3390/rs10030462

M3 - Article

AN - SCOPUS:85044217084

VL - 10

JO - Remote Sensing

JF - Remote Sensing

SN - 2072-4292

IS - 3

M1 - 462

ER -