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Abstract:
We apply synthetic aperture radar data and geophysical modeling to assess ground deformation changes at the
284 km2
large Toktogul Reservoir in Kyrgyzstan, Central Asia, which is used for hydropower generation and irrigation.
The reservoir’s water level is prone to significant changes during the year, but also shows inter-annual
variations due to overall water recession or accumulation. We use Envisat ASAR data to analyse the ground deformation
during a time of exaggerated use of water between 2004 – 2009 (net water level drop of 60 m / 13.5 km3
) and
Sentinel-1 data to derive the ground deformation during a time of overall water level increase between 2014 – 2016
(net water level plus of 51 m / 11.2 km3
). The deformation pattern was measured by generating an interferometric
time-series using the Small BAseline Subset (SBAS) approach. After removing heavily impacting atmospheric
effects by applying the elevation dependent powerlaw approach, results show that both sensors are able to image
related uplift and subsidence signals in the order of approximately 1 mm per 1 m water level change for the investigated
time periods. Moreover, time-series results from Sentinel-1 also resolve intra-annual changes induced by
40 m periodical water level changes. Reasons for this superior behaviour of Sentinel-1 data are a short temporal
baseline of 12 days and a small orbital tube, which both lead to a higher temporal sampling compared to the Envisat
setting and at the same time to a better correlation of points within the interferograms. The derived spatial
pattern of land-deformation rate is validated against modeling of the elastic deformation, based on a Love-number
approach. The load forcing due to lake-level changes is derived from satellite-based radar altimetry.
