Remote sensing of recent changes in northern peatlands

Peatlands are organic-rich wetlands, where waterlogged conditions allow carbon-rich detritus to accumulate. Despite covering less than 3 % of the Earth's land surface (Xu & Morris et al., 2018), peatlands are thought to store between a sixth and a third of all global soil carbon (Gorham, 1991; Page et al., 2011). By far the largest concentrations of these important landscapes are in the mid- and high-latitudes of the northern hemisphere, particularly northern Canada, Scandinavia and Western Siberia (Tarnocai et al., 2009). These areas have experienced rapid climate change in recent decades, and are projected to continue to warm more rapidly than almost anywhere else on the planet over the coming century (Collins et al., 2013; Cohen et al., 2014). Concern exists that the northern peatland carbon store may be vulnerable to rapid changes in climate, and that thousands of years' worth of accumulated carbon may be returned to the atmosphere as these systems begin to warm and dry (Ise et al., 2008; Ciais et al., 2013).

Despite this importance of northern peatlands to global biosphere-climate feedbacks, large knowledge gaps exist about how these ecosystems are currently changing in response to recent climate change. This project will assess changes in the hydrology, vegetation and geomorphology of northern peatlands during recent decades, on spatial scales ranging from the continental to individual field sites. There is potential for measuring changes in peatland surface wetness, for instance the widespread development of thermokarst lakes, using a range of classification approaches (e.g. normalised difference wetness index (NDWI), segmentation-based classification); while changes in vegetation, increasingly apparent in a "greening Arctic", may be assessed using the normalised difference vegetation index (NDVI). There is the opportunity to quantify surface lowering using either repeat optical DEMs, altimetry or interferometry, and at smaller spatial scales, geomorphological changes such as expansion and contraction of peatland pools could be assessed by analysing repeat aerial photography, including drone surveys, and possibly also historical air imagery that is available in Alaska, northern Scotland and other peat-rich regions. This more detailed analysis is likely to employ cutting-edge techniques such as Structure-from-Motion and laser scanning that have been extensively employed elsewhere by the supervisory team (e.g., Smith et al., 2016) as well as more traditional field-based techniques. Gridded instrumental climate data will be used to explain any temporal trends yielded by these analyses along with other geomorphological and topographical controls.

There will be exciting opportunities for the student to visit remote field sites, including in the Arctic, to ground-truth interpretations of satellite data and to collect aerial drone photographic surveys. The student will also be encouraged to build collaborations with the broad group of international experts working in this topical area.

This project will use a powerful combination of remote sensing techniques at a range of scales, and instrumental climate data, to study recent changes in northern peatlands at a range of scales. More specifically, the project will address the following objectives:
1. To detect and quantify recent changes in the vegetation and surface wetness of northern peatlands across large areas of the northern hemisphere, using satellite imagery.
2. To detect and quantify changes in vegetation, surface wetness and geomorphology in northern peatlands, at smaller spatial scales (e.g., regional scales to specific peatland sites) during recent decades, using a time series of drone photography mosaics and Structure-from-motion.
3. To establish the role of recent climate change in driving these recent changes in northern peatlands.