Mapping Palsa and Peat Plateau Changes in the Hudson Bay Lowlands, Canada, Using Historical Aerial Photography and High-Resolution Satellite Imagery

Abstract

Intensified warming in northern high latitudes drives widespread permafrost loss. Applying remote sensing methods to monitor the southern portion of the discontinuous permafrost zone in northern Ontario has provided information about the dynamics of permafrost change since air photography became available. The degradation rate and spatial pattern of permafrost thaw were tracked using a 435-km2 study area located about 30 km east of Victor Diamond Mine and 55 km west of Attawapiskat First Nation, Ontario. Permafrost in this area occurs mainly in vegetated palsas and peat plateaus covered by dense black spruce. Vegetation signatures, texture, and circular-to-elongated shapes are key image interpretation elements used to detect palsas and peat plateaus. Changes over a period of 57 years were mapped using object-based image analysis on orthorectified air photos from 1954–1955 and WorldView-2 satellite imagery acquired in 2011. Field validations were conducted through aerial and ground surveys in 2014 and 2016. The resulting change map demonstrates that permafrost degradation is leading over aggradation in the area. The permafrost area decreased by 1.2%, from 4.5% in 1954 to 3.3% in 2011. The patterns of change in palsa distribution have been analyzed, and accelerated palsa degradation is linked to proximity to streams.