Active-layer thickness estimation from X-band SAR backscatter intensity

Abstract

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 R 2 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.

Linking tundra vegetation, snow, soil temperature, and permafrost

“…Conversely, its predictive value in summer is poor. The generally weak relationship between vegetation type and active layer thickness we found in our study hinders upscaling approaches such as in Nelson et al (1997); Widhalm et al (2017). This is likely related to variable soil thermal properties, as one would expect a strong relation between thawing degree days and active layer thickness for uniform soil properties.…”

Scattering Characteristics of X-, C- and L-Band PolSAR Data Examined for the Tundra Environment of the Tuktoyaktuk Peninsula, Canada

“…In contrast, use of short wavelengths (X-and C-Band) is beneficial for characterizing tundra and wetland vegetation. This observation is in accordance with other studies [9,12,15].…”

Remote sensing evaluation of High Arctic wetland depletion following permafrost disturbance by thermo-erosion gullying processes

“…Additional strategies to increase differentiation between nondisturbed wet and mesic vegetation communities may include considering plant structure and variations in soil moisture (Laidler and Treitz 2003;Laidler et al 2008;Atkinson and Treitz 2012) as well as using other high-resolution remote sensing platforms. In this regard, unmanned aerial vehicles, which are relatively inexpensive and have successfully been tested for monitoring temporal dynamics of landslide and tundra vegetation (Turner et al 2015;Fraser et al 2016), as well as airborne laser scanning and interferometric synthetic aperture radar used to monitor topographic changes and active layer thickness (Gangodagamage et al 2014;Liu et al 2014;Schaefer et al 2015;Widhalm et al 2017) represent complementary techniques full of potential.…”

“…Techniques such as InSAR (interferometric synthetic aperture radar) as well as airbone and terrestrial laser scanning have been used to document detailed topographical changes (Chen et al 2013;Hubbard et al 2013;Liu et al 2014;Wolfe et al 2014), thermokarst (Barnhart and Crosby 2013), active layer thickness (Gangodagamage et al 2014;Schaefer et al 2015;Widhalm et al 2017), and freeze-thaw cycles (Daout et al 2017). While remote sensing studies have also characterized the distribution of thermo-erosion landforms (Morgenstern 2012;Belshe et al 2013;Godin et al 2014), they have yet to examine the impacts of these processes on surrounding vegetation.…”