Active-layer thickness estimation from X-band SAR backscatter intensityстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 24 октября 2018 г.
Аннотация:The active layer above the permafrost, which sea-sonally thaws during summer, is an important parameter formonitoring the state of permafrost. Its thickness is typicallymeasured locally, but a range of methods which utilize in-formation from satellite data exist. Mostly, the normalized difference vegetation index (NDVI) obtained from opticalsatellite data is used as a proxy. The applicability has beendemonstrated mostly for shallow depths of active-layer thick-ness (ALT) below approximately 70 cm. Some permafrost ar-eas including central Yamal are, however, characterized bylarger ALT. Surface properties including vegetation structureare also represented by microwave backscatter intensity. Sofar, the potential of such data for estimating ALT has not beenexplored. We therefore investigated the relationship between ALT and X-band synthetic aperture radar (SAR) backscat-ter of TerraSAR-X (averages for 10×10 m window) in orderto examine the possibility of delineating ALT with continu-ous and larger spatial coverage in this area and compare it tothe already-established method of using NDVI from Land-sat (30 m). Our results show that the mutual dependency ofALT and TerraSAR-X backscatter on land cover types sug-gests a connection of both parameters. A range of 5 dB canbe observed for an ALT range of 100 cm (40–140 cm), andanR2of 0.66 has been determined over the calibration sites.An increase of ALT with increasing backscatter can be de-termined. The root mean square error (RMSE) over a com-parably heterogeneous validation site with maximum ALT of>150 cm is 20 cm. Deviations are larger for measurement lo-cations with mixed vegetation types (especially partial cover-age by cryptogam crust) with respect to the spatial resolutionof the satellite data.