Widhalm, Barbara; Bartsch, Annett; Leibman, Marina O; Khomutov, Artem V (2017): Mean TerraSAR-X backscatter and in-situ measurements of near surface soil moisture and temperature including vegetation survey in August 2015 on central Yamal (Vaskiny Dachi CALM site) [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.874619,

---

Supplement to: Widhalm, B et al. (2017): Active-layer thickness estimation from X-band SAR backscatter intensity. The Cryosphere, 11(1), 483-496, https://doi.org/10.5194/tc-11-483-2017

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.

In August 2015, a dedicated vegetation survey was carried out at the Vaskiny Dachi CALM site on the central Yamal Peninsula in North-West Russia. For each CALM grid point, the dominant vegetation cover within a 3 x 3m area was determined. The following classes are distinguished: cryptogam crust, low shrubs (<15 cm), medium shrubs (15-30 cm), high shrubs (>30 cm), grass and moss, a class where sedges dominate and classes of mixed vegetation.

Furthermore soil moisture and temperature measurements were conducted at the CALM grid. A Delta-T WET Sensor with a handheld HH2 Moisture Meter was used to measure the moisture content and temperature of the top 5 cm at each grid point on three dates in August 2015.

Six TerraSAR-X images from August 2014 and 2015 (three images per year) were orthorectified and radiometrically normalized. The mean values of these processed images were extracted for each CALM grid point.

TerraSAR-X data has been made available by DLR through PI agreement LAN1706 and HYD2522.