Can C-band synthetic aperture radar be used to estimate soil organic carbon storage in tundra?

Abstract

Abstract.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.

Characterizing permafrost active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska

“…A close association between SOC and local topographic attributes, including soil wetness, has been reported (Mishra and Riley, 2015); this may explain why model simulations derived using a statistical SOC distribution following the radar SM pattern produced better ALT performance than the radar retrievals. Other potential geophysical retrievals from multi-frequency radar remote sensing -including SOC, freeze-thaw, and SM profile (Du et al, 2015;Bartsch et al, 2016) -may enable improved model representation of processes affecting permafrost active layer conditions.…”

Simplified Normalization of C-Band Synthetic Aperture Radar Data for Terrestrial Applications in High Latitude Environments

“…Furthermore, the vegetation classes of the CAVM can be divided into different wetness classes which were used to delineate backscatter thresholds. Further investigations by Bartsch et al [14] showed that this minimum winter backscatter dataset could also be applied as a proxy to estimate soil organic carbon within the upper meter.…”

“…It was shown that by using minimum winter backscatter values of the GM time series, vegetation physiognomy units of specific wetness regimes could be differentiated for the Arctic region north of the tree line. Further, Bartsch et al [14] used GM frozen backscatter as a proxy for soil organic carbon. A so called 'dry reference' is also essential for the retrieval of relative soil moisture from radar data [5], which can be derived using frozen conditions.…”

“…A so called 'dry reference' is also essential for the retrieval of relative soil moisture from radar data [5], which can be derived using frozen conditions. In these studies a pixel based approach for normalization was chosen and the linear model derived for the Arctic studies [13,14] based on an average of 46 ASAR GM acquisitions per location. ASAR GM does however only provide 1 km spatial resolution and higher spatial resolution is needed in order to capture the heterogeneity of Arctic environments [15].…”

“…ASAR GM does however only provide 1 km spatial resolution and higher spatial resolution is needed in order to capture the heterogeneity of Arctic environments [15]. It has been demonstrated that applications developed for GM can be transferred to data from ASAR operating in Wide Swath (WS) mode (150 m) and they can provide much higher detail and actual landscape patterns [14]. It is therefore expected that Sentinel-1, with a resolution of 93 m × 87 m (range × azimuth) in EW GRDM (Extra Wide Swath, Ground Range Detected Medium Resolution) mode is of further benefit.…”