ALBERT

Description: The data set presents results from geospatial analyses of a region in Central Yamal, Western Siberia, which was affected by the construction of the Bovanenkovo railway line and by high Retrogressive Thaw Slumps (RTS) occurrence in consequence of the extremely warm and wet year 2012. A change detection was performed using high resolution optical satellite images from 2010 (GeoEye-1) and 2013 (QuickBird). The preprocessing of the satellite data (orthorectification and atmospheric correction) was performed by and is described in Dvornikov et al., 2016. The degree of disturbance change from 2010 and 2013 around the railway line was classified into three major disturbance levels - low, medium and high, based on the width of disturbance and magnitude of change over the course of three years. A kernel density raster file illustrates RTS distribution. The highest disturbance along the railway can be observed, where the RTS activity is the highest in 2013.

Description: The datasets present measurements of cDOM absorption of lakes located in Central Yamal regularly from the summer periods of 2011 on. The study region is in the central part of Yamal peninsula (Western Siberia, Russia) with the long-term research station Vaskiny Dachi. Vaskiny Dachi has been established in 1988 as permafrost monitoring site, since 1996 it is run by the Earth Cryosphere Institute (ECI), Siberian Branch of Russian Academy of Sciences and an established site for the international Global Terrestrial Network for Permafrost (GTN-P) program. Water samples were collected in calm weather conditions with bottle sampling from the upper 30 cm of water column close to the shore or in the center of lakes from boat. The coastal rim of several lakes on the high plains is affected by recent activation of thermocirques. The samples for CDOM were filtrated directly in the field after sampling. Filtrates for CDOM were prepared by filtrating through 0.7µm pore size glass fiber filters (Whatman) and were stored in cold and dark conditions to avoid the photodegradation of CDOM. CDOM filtrates have been measured after the expedition using the dual-beam Specord 200 laboratory spectrometer (Jena Analytik) at the Otto Schmidt Laboratory OSL, Arctic and Antarctic Research Institute, St. Petersburg, Russia. The OSL CDOM protocol (Heim and Roessler, 2016) prescribes 3 Absorbance (A) measurements per sample from UV to 750 nm against ultra-pure water. The absorption coefficient, a, is calculated by a = 2.303A/L, where L is the pathlength of the cuvette [m], and the factor 2.303 converts log10 to loge. The output of the calculation is a continuous spectrum of a. The CDOM a spectra are used to determine the exponential slope value for specific wavelength ranges, S by fitting the data between min and max wavelength to an exponential function. We provide CDOM absorption coefficients for the wavelengths 254, 260, 350, 375, 400, 412, 440, 443 nm [1/m] and Slope values for three different UV, VIS, wavelength ranges: 275 to 295 nm, 350 to 400 nm, 300 to 500 nm [1/nm]. All data sampling and processing were carried out by scientists from Earth Cryosphere Institute and Alfred Wegener Institute.

Description: 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.

Description: Shallow lakes are common across the entire Arctic. They play an important role as methane sources and wildlife habitats, and they are also associated with thermokarst processes which are characteristic of permafrost environments. Many lakes freeze to the ground along their rims and often over the entire extent during winter time. Knowledge on the spatial patterns of ground-fast and floating ice is important as it relates to methane release, talik formation and hydrological processes, but no circumpolar account of this phenomenon is currently available. Previous studies have shown that ground-fast ice can easily be detected using C-band Synthetic Aperture Radar (SAR) backscatter intensity data acquired from satellites. A major challenge is that backscatter intensity varies across the satellite scenes due to incidence angle effects. Circumpolar application therefore requires the inclusion of incidence angle dependencies into the detection algorithm. An approach using ENVISAT ASAR Wide Swath data (approximately 120 m spatial resolution) has therefore been developed supported by bathymetric measurements for lakes in Siberia. This approach was then further applied across the entire Arctic for late winter 2008. Analyses of lake depth measurements from several sites suggest that the used method yields the potential to utilize ground-fast lake ice information over larger areas with respect to landscape development, but results need to be treated with care, specifically for larger lakes and along river courses. Lakes like the Great Slave Lake, Great Bear Lake and lakes located in the proximity of the Putorana Plateau were excluded from the analyses.