ALBERT

Description: A new approach for the estimation of Soil Organic Carbon (SOC) pools North of the tree line has been developed based on synthetic aperture radar data (SAR). SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C-band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 PgC are stored in the upper 30 cm of soils North of the tree line. This is approximately 25 % less than stocks derived from the soil map based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands as well as strongly cryoturbated soils. The approach does however provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7 x 7 km in NE Siberia. The approach can be also potentially transferred to medium resolution C-band SAR data such as ENVISAT ASAR Wide Swath with 120 m resolution but it is in general limited to regions without woody vegetation. Comparisons to the length of unfrozen period indicates the suitability of this parameter for modelling of the spatial distribution of soil organic carbon storage.

Description: A new approach for the estimation of soil organic carbon (SOC) pools north of the tree line has been developed based on synthetic aperture radar (SAR; ENVISAT Advanced SAR Global Monitoring mode) data. SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 Pg C is stored in the upper 30 cm of soils north of the tree line. This is approximately 25 % less than stocks derived from the soil-map-based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands or strongly cryoturbated soils. The approach does, however, provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7  ×  7 km in NE Siberia. The approach can be also potentially transferred to medium-resolution C-band SAR data such as ENVISAT ASAR Wide Swath with  ∼  120 m resolution but it is in general limited to regions without woody vegetation. Global Monitoring-mode-derived SOC increases with unfrozen period length. This indicates the importance of this parameter for modelling of the spatial distribution of soil organic carbon storage.

Description: A new approach for the estimation of soil organic carbon (SOC) pools north of the tree line has been developed based on synthetic aperture radar (SAR; ENVISAT Advanced SAR Global Monitoring mode) data. SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 Pg C is stored in the upper 30 cm of soils north of the tree line. This is approximately 25 % less than stocks derived from the soil-map-based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands or strongly cryoturbated soils. The approach does, however, provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7 × 7 km in NE Siberia. The approach can be also potentially transferred to medium-resolution C-band SAR data such as ENVISAT ASAR Wide Swath with ~120 m resolution but it is in general limited to regions without woody vegetation. Global Monitoring-mode-derived SOC increases with unfrozen period length. This indicates the importance of this parameter for modelling of the spatial distribution of soil organic carbon storage.

Description: Permafrost cannot be directly detected from space, but many surface features of permafrost terrains and typical periglacial landforms are observable with a variety of EO sensors ranging from very high to medium resolution at various wavelengths. In addition, landscape dynamics associated with permafrost changes and geophysical variables relevant for characterizing the state of permafrost, such as land surface temperature or freeze-thaw state can be observed with space-based Earth Observation. Suitable regions to examine environmental gradients across the Arctic have been defined in a community white paper (Bartsch et al. 2014). These transects have been revised and adjusted within the DUE GlobPermafrost initiative of the European Space Agency. The ESA DUE GlobPermafrost project develops, validates and implements Earth Observation (EO) products to support research communities and international organisations in their work on better understanding permafrost characteristics and dynamics. Prototype product cases will cover different aspects of permafrost by integrating in situ measurements of subsurface properties and surface properties, Earth Observation, and modelling to provide a better understanding of permafrost today. The project will extend local process and permafrost monitoring to broader spatial domains, support permafrost distribution modelling, and help to implement permafrost landscape and feature mapping in a GIS framework. It will also complement active layer and thermal observing networks. Both lowland (latitudinal) and mountain (altitudinal) permafrost issues are addressed. The status of the Permafrost Information System and first results will be presented. Prototypes of GlobPermafrost datasets include: - Modelled mean annual ground temperature by use of land surface temperature and snow water equivalent from satellites - Land surface characterization including shrub height, land cover and parameters related to surface roughness - Trends from Landsat Time series over selected transects - For selected sites: subsidence, ground fast lake ice, land surface features and rock glacier monitoring

Description: Permafrost is stated as an essential climate variable by the World Meteorological Organization and is an important physical landscape component of high-latitude environments. The variability of the permafrost ecosystem parameters soil moisture (SM) as well as freeze-thaw (FT) has a strong impact on rapid permafrost degradation, on surface energy and water fluxes as well as on biogeochemical processes. Thus information about the mentioned parameters in high temporal and spatial resolution is important for the understanding of processes in permafrost landscapes. Synthetic aperture radar (SAR) operates independently of cloud coverage and polar night and today’s SAR satellite systems provide imagery with high temporal and spatial resolution. Existing operational satellite SAR data products of SM and FT are available only in coarse-scale resolution. We are investigating high-spatial resolution SAR of TerraSAR-X (TSX), and in future ALOS-2, Sentinel-1, as well as optical very high resolution satellite imagery in combination with in-situ experimental monitoring data to investigate the spatiotemporal variability of permafrost disturbances, SM and FT on the watershed scale. Our study site for rapid permafrost degradation is an actively eroding ice- and organic-rich permafrost riverbank from the so called Ice-Complex within the central Lena Delta, Siberia. Our studies on SM and FT focus on a small scale watershed on Herschel Island along the western Yukon Coast, Canada and can potentially be transferred to the Ice-Complex permafrost landscape in the Lena Delta. Automated micro-stations with near to surface soil moisture and temperature sensors were installed in the Lena Delta (since 2013) and on Herschel Island (since 2015). Field work on Herschel Island and the Lena Delta included handheld soil moisture measurements as well as extensive soil sampling. In spring 2015 we conducted a GPS survey in the Lena Delta along the test site and installed a time-lapse camera as well as wooden poles with 50cm distance perpendicular to a rapidly eroding cliff top sequence. Time-lapse images were acquired from late June to late August. We used TSX backscatter time-series from the years 2012, 2013, 2014 and 2015 to analyze rapidly eroding cliff tops along the riverbank within the central Lena Delta. Pre-processing was performed using the Next ESA SAR toolbox (NEST) and included radiometric calibration and conversion to backscatter coefficient sigma nought, multilooking and an ellipsoid corrected geocoding. We then used a threshold approach to visualize the transition line between undisturbed tundra surface and actively eroding cliff prior to mapping. Very high resolution orthorectified optical satellite images acquired in August 2010 and August 2014 were used as validation datasets for the TSX-derived results. The TSX extracted annual retreat rates are in the same range as the ones from the optical reference dataset. The intra-annual TSX-derived cliff top retreat lines from 2014 at the test site showed rates of 2 to 3 m per month. The time-lapse field data at the same place showed similar results in summer 2015. The TSX backscatter time-series show a high potential for the monitoring of rapid permafrost degradation with high spatial and temporal resolution. The results are valuable for the understanding of intra-seasonal permafrost degradation dynamics. Future work on Herschel Island and the Lena Delta will focus on soil moisture and freeze/thaw dynamics on the watershed scale. ALOS-2, Sentinel-1 and TSX datasets are planned to be used and cross-validated with the field datasets. The presented project is embedded in the German Helmholtz Alliance Earth System Dynamics (EDA) network and builds on existing datasets from the FP7 within the PAGE21 project. TSX-datasets were kindly provided by the Department Land Surface from the German Aerospace Agency (DLR).

Description: Ongoing Arctic warming changes arctic landscapes in various ways. It potentially alters the organic matter supply to lakes in the Arctic. Arctic warming may increase vegetation density in the catchments of lakes and thus increase of the organic matter supply to the lakes can be expected. Furthermore, warming may cause an increase of ground temperature and deepening of the active layer in permafrost soils, and thus activate various cryogenic processes including thermodenudation (Leibman et al. 2015). We present results of study of colored dissolved organic matter (CDOM) in thermokarst lakes of the central Yamal peninsula (Western Siberia, Russia) and the interconnection of CDOM with lake and catchment characteristics. We used a complex approach including field observations, laboratory measurements, and high spatial resolution optical and synthetic aperture radar (SAR) remote sensing and geographical information system (GIS) data analysis. CDOM absorption and spectral slope values, and suspended particulate matter concentrations (SPM) in several thermokarst lakes were obtained during 2011 – 2015 field campaigns. Availability of very high spatial resolution (GeoEye-1, WorldView-2) and high spatial resolution (SPOT5) optical satellite images as well as high resolution TanDEM-X DEM data, TSX and ALOS PALSAR SAR satellite images for the study area allowed to produce a large dataset of lake and catchment-related parameters (n=18). CDOM absorption at 440 nm in 363 lakes was retrieved from optical satellite images (correlation with in-situ data: R^2=0.68, n=24) using the band ratio method of Kutser et al. (2005). We also detected that increased turbidity in some of the lakes due to wind events in some of the optical satellite acquisitions affect the accuracy of retrieved CDOM values. The statistical analysis “boosted regression tree” was applied in order to find the most important variables controlling the CDOM concentration in central Yamal thermokarst lakes. The results show the following most important variables: the lake area/lake catchment area ratio, the elevation of the lake (i.e., floodplain or non-floodplain lake), median value of the Normalized Difference Vegetation Index (NDVI) of the lake catchment, activity of thermodenudation (thermocirques above the shore line) and total snow water equivalent (SWE) in the lake catchment. In this analysis we used a representative data of approximately 350 square kilometers including all geomorphic terrace levels and the floodplains of Se-Yakha and Mordy-Yakha rivers. Annual concentrations of CDOM in Yamal thermokarst lakes also differed. We found the clear relation of CDOM absorption values to climatic controls (summer air temperature and atmospheric precipitation) and recent activation of thermocirque in the study region. The enhanced erosion of the lake cliffs and enhanced atmospheric precipitation may increase the inflow of fresh terrestrial organic matter into the lakes from the surrounding catchments. Activation of thermocirques controls the additional input of SPM and CDOM into the lake water influencing also the lake color. References: Kutser T, Pierson DC, Kallio K, Reinart A, Sobek S. 2005. Mapping lake CDOM by satellite remote sensing. Remote Sensing of Environment 94: 535–540 DOI:10.1016/j.rse.2004.11.009 Leibman MO, Khomutov AV, Gubarkov AA, Mullanurov DR, Dvornikov YA. 2015. The research station “Vaskiny Dachi”, Central Yamal, West Siberia, Russia – A review of 25 years of permafrost studies. Fennia 193: 3–30.

Description: Arctic warming accelerates the rapid degradation of ice- and organic-rich permafrost landscapes through thermokarst and thermal-erosion. These processes lead to the retreat of ice-rich coasts, riverbanks, lake shorelines, to surface subsidence and gullying. The subsequent reactivation of ancient carbon previously stored in the eroded ice- and organic-rich sediments could have tremendous impact on the carbon cycle from regional to global scale. Yet, information at high temporal and spatial resolution is often lacking to describe the rates and the timing of permafrost degradation. Synthetic aperture radar (SAR), which operates independently of atmospheric distortions, is particularly valuable to alleviate these issues because of its potential for high temporal resolution monitoring in a region where cloud cover often limits the use of optical satellite imagery. In this study, we used SAR data to investigate the spatiotemporal dynamic of a rapidly degrading ice- and organic-rich up to 50-m-high and 2000-m long riverbank in the central Lena Delta. Our main objectives were to 1) assess the applicability of synthetic aperture radar (SAR) satellite data for high-temporal resolution monitoring of rapidly eroding riverbanks and 2) to identify the seasonal timing of ice-rich permafrost riverbank erosion. We analyzed a unique time-series of high-spatial and temporal SAR images from the German TerraSAR-X (TSX) satellite, operating in X-band wavelength, as well as very high resolution optical satellite imagery and in-situ time-lapse data. We processed 77 HH- polarized SAR backscatter images with acquisition dates between August 2012 and October 2015. The imagery was first pre-processed using the Sentinel-1 toolbox from the European Space Agency. We then applied a thresholding to better identify the transition line from undisturbed tundra surface to the actively eroding cliff we refer to as cliff top line. We then calculated cliff top retreat rates and finally compared these with environmental baseline data to identify the main driving factors of riverbank retreat. Visual interpretation of the TSX time-series showed that the cliff of the riverbank is only visible in the months June to October. Annual erosion rates were in the same range when comparing the optical reference with the SAR datasets. The in-situ time-lapse data for the summer of 2015 showed similar results for the intra-annual erosion compared to the SAR derived results. Based on the SAR dataset we detected mostly constant erosion rates at our test site throughout the thawing period for the years 2013, 2014 and 2015. Our results show that the cliff-top at the test site retreats constantly over the thawing season rather than event driven (i.e. through the spring peak discharge only). The studied cliff top is protected from spring flood events by sandbanks in front of the riverbank. However, runoff caused by permafrost thaw, precipitation and flooding will degrade the protecting sand banks and consequently will lead to a reconnection of the cliff system to the Lena River System, even when water level is lower towards the end of the thawing season. We conclude that x-band backscatter time-series are valuable for monitoring rapid permafrost degradation with high spatial and temporal resolution. Our results indicate that cliff top erosion of ice-rich riverbanks takes place constantly over the thawing period and is not event driven.