Decadal Change in Northern Wetlands Based on Analysis of ALOS/PALSAR and JERS SAR Data

Northern wetlands are believed to have hitherto served as carbon sinks, sequestering about one third of the total global pool of soil carbon. The warmer, drier conditions expected throughout the Arctic as a consequence of global warming may induce aerobic decomposition of northern wetland soils, which may cause them to become major sources rather than sinks of carbon dioxide. It is therefore critical to develop an ability to monitor long-term changes occurring in the condition of northern wetlands. Since L-Band synthetic aperture radar (SAR) is sensitive to vegetation structure, biomass, and moisture content, it is an appropriate choice for detecting changes in the characteristics of vegetated wetlands. We have used L-band SAR imagery from two different spaceborne sensors separated in time by approximately one decade, JERS and ALOS/PALSAR, to produce a thematic map of change in the type and extent of representative regions of wetlands in Alaska, such as tundra, scrub/shrub, and forested wetlands. JERS imagery characterizes the wetlands status for the 1997 time frame while dual-polarized ALOS/PALSAR imagery captures the wetlands status for the 2007 time frame. To produce each classified wetlands map, the SAR imagery is supplemented with the corresponding imagery collection dates, a digital elevation model (DEM), a slope model, an open water mask, proximity to water map, and geographic latitude. The classification algorithm applied to each set of imagery is based upon using a multitude of decision trees. The accuracy of the resulting thematic change map will be verified using ground reference data. The results could demonstrate the utility of multi-platform satellite SAR observations for characterizing the transitions across multiple years in extent and type of vegetated wetlands as a result of global climate change.