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Advisor(s)
Abstract(s)
Thermokarst lakes and ponds are a common landscape feature resulting from permafrost thaw, but their intense greenhouse
gas emissions are still poorly constrained as a feedback mechanism for global warming because of their diversity, abundance,
and remoteness. Thermokarst waterbodies may be small and optically diverse, posing specifc challenges for optical remote
sensing regarding detection, classifcation, and monitoring. This is especially relevant when accounting for external factors that afect water refectance, such as scattering and vegetation shadow casts. In this study, we evaluated the efects of
shadowing across optically diverse waterbodies located in the forest–tundra zone of northern Canada. We used ultra-high
spatial resolution multispectral data and digital surface models obtained from unmanned aerial systems for modeling and
analyzing shadow efects on water refectance at Earth Observation satellite overpass time. Our results show that shadowing
causes variations in refectance, reducing the usable area of remotely sensed pixels for waterbody analysis in small lakes
and ponds. The efects were greater on brighter and turbid inorganic thermokarst lakes embedded in post-glacial silt–clay
marine deposits and littoral sands, where the mean refectance decrease was from -51 to -70%, depending on the wavelength.
These efects were also dependent on lake shape and vegetation height and were amplifed in the cold season due to low
solar elevations. Remote sensing will increasingly play a key role in assessing thermokarst lake responses and feedbacks
to global change, and this study shows the magnitude and sources of optical variations caused by shading that need to be
considered in future analyses.
Description
Keywords
Shadows Optical remote sensing Thermokarst Unmanned aerial systems Vegetation Lakes
Pedagogical Context
Citation
Freitas, P., Vieira, G., Mora, C., & Vincent, W. F. (2022). Vegetation shadow casts impact remotely sensed reflectance from permafrost thaw ponds in the subarctic forest-tundra zone. Environmental Earth Sciences, 8, 522. https://doi.org/10.1007/s12665-022-10640-1
Publisher
Springer