Satellite radar imagery for monitoring inland wetlands in boreal and sub‐arctic environments

Abstract

ABSTRACT1. Knowledge about the distribution and types of wetlands is in high demand by ecosystem modellers for full greenhouse gas accounting. The scope of this paper is to demonstrate the suitability of satellite radar data for the delineation of wetlands in the tundra and boreal forest biomes of central Siberia.2. An area of more than 3 million km 2 in central Siberia was investigated using satellite data. It covers freshwater ecosystems of the tundra and non-forested peatlands in tundra and boreal forest biomes. The satellite data represent the growing seasons of 2003/2004. 3. Microwave data were acquired by the Advanced Synthetic Aperture Radar (ASAR) instrument onboard ENVISAT. The multi-temporal capabilities and resolution (150 m  150 m in WS mode) of the ASAR wide swath mode enabled the detection of dynamic features >2 ha over this vast area. Scatterometer (QuikScat) data could be employed to distinguish hydro-periods.4. Wetland types have been identified on the basis of seasonal changes in backscatter. In a first step scatterometer data were used to identify the transition period from frozen to unfrozen conditions over a range of 158 latitude. Inundation patterns and soil moisture changes could be identified for the different hydro-periods and used to classify wetlands. Results for peatlands have been compared with Russian forest inventory data which contain information on wetland distribution.5. The database of permanently inundated areas is an intermediate product which enables the mapping of wetlands in two ways: (1) identification of seasonal inundation in relation to snowmelt and high permafrost tables and (2) input for density analysis of permanent small and shallow lakes in tundra areas which are important freshwater ecosystems as well as a methane source. Differences in intensity and duration of soil moisture conditions allow the identification of peatlands.

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

“…They are commonly gridded to 75 m × 75 m (e.g. Bartsch et al, 2007;Santoro et al, 2011;Reschke et al, 2012).…”

“…Regions with soil conditions close to saturation near the surface can be therefore identified using SAR data. This has been demonstrated applicable for peatland detection at high latitudes with C band (Bartsch et al, 2007(Bartsch et al, , 2009Reschke et al, 2012). The wet and at the same time high SOC areas have a low bulk density over several tens of centimetres and are water/ice-rich (more than 60 % at, for example, Kytalyk, Weiss et al, 2016).…”

Capability of C-Band SAR for Operational Wetland Monitoring at High Latitudes

“…Open peatlands can be identified with C-band SAR due to their higher moisture content and thus higher backscatter [15,27]. The backscatter of long-term saturated areas is therefore high in a single image, but not always separable from high backscatter caused by other land cover at that time step.…”

“…Other high but short-term backscatter sources can be wet surfaces due to recent rain, or the shorelines of drying ponds. Assuming that peatland areas change more slightly over the year than other areas, they show seasonal backscatter statistics distinct from other land cover classes [27]. Other land cover features with a long-term hS W and thus similar seasonal backscatter statistics are floodplains (which stay moist when the groundwater table is high) or water accumulations due to recent forest fires [28,29].…”

“…In addition to the statistical measures, the slope calculated from the circumpolar DUE Permafrost Digital Elevation Model [30] was used. The minimum and maximum of time series data (Method 1) were chosen under the assumption that areas of peatlands have higher dB values than most other land cover classes at these specific statistic measures [27]. They were calculated pixel-wise from all available datasets within the time series period of May to September (t 1 = first date, t n = last date) of the years 2007 and 2008.…”