Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 11, 483-496, 2017
http://www.the-cryosphere.net/11/483/2017/
doi:10.5194/tc-11-483-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
10 Feb 2017
Active-layer thickness estimation from X-band SAR backscatter intensity
Barbara Widhalm1, Annett Bartsch1,2, Marina Leibman3,4, and Artem Khomutov3,4 1Zentralanstalt für Meteorologie und Geodynamik, Division Data, Methods and Modelling, 1190 Vienna, Austria
2Vienna University of Technology, Department of Geodesy and Geoinformation, 1040 Vienna, Austria
3Earth Cryosphere Institute, Russian Academy of Sciences, Siberian Branch, Tyumen 625000, Russia
4Tyumen State University, Department of Cryosophy, Tyumen 625006, Russia
Abstract. The active layer above the permafrost, which seasonally thaws during summer, is an important parameter for monitoring the state of permafrost. Its thickness is typically measured locally, but a range of methods which utilize information from satellite data exist. Mostly, the normalized difference vegetation index (NDVI) obtained from optical satellite data is used as a proxy. The applicability has been demonstrated mostly for shallow depths of active-layer thickness (ALT) below approximately 70 cm. Some permafrost areas including central Yamal are, however, characterized by larger ALT. Surface properties including vegetation structure are also represented by microwave backscatter intensity. So far, the potential of such data for estimating ALT has not been explored. We therefore investigated the relationship between ALT and X-band synthetic aperture radar (SAR) backscatter of TerraSAR-X (averages for 10  ×  10 m window) in order to examine the possibility of delineating ALT with continuous and larger spatial coverage in this area and compare it to the already-established method of using NDVI from Landsat (30 m). Our results show that the mutual dependency of ALT and TerraSAR-X backscatter on land cover types suggests a connection of both parameters. A range of 5 dB can be observed for an ALT range of 100 cm (40–140 cm), and an R2 of 0.66 has been determined over the calibration sites. An increase of ALT with increasing backscatter can be determined. The root mean square error (RMSE) over a comparably heterogeneous validation site with maximum ALT of  >  150 cm is 20 cm. Deviations are larger for measurement locations with mixed vegetation types (especially partial coverage by cryptogam crust) with respect to the spatial resolution of the satellite data.

Citation: Widhalm, B., Bartsch, A., Leibman, M., and Khomutov, A.: Active-layer thickness estimation from X-band SAR backscatter intensity, The Cryosphere, 11, 483-496, doi:10.5194/tc-11-483-2017, 2017.
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Short summary
The active layer above the permafrost, which seasonally thaws during summer, is an important parameter for monitoring the state of permafrost. Its thickness is typically measured locally. The relationship between active-layer thickness (ALT) and X-band SAR backscatter of TerraSAR-X has been investigated in order to explore the possibility of delineating ALT with continuous and larger spatial coverage.
The active layer above the permafrost, which seasonally thaws during summer, is an important...
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