| Title | Landsat-based mapping of thermokarst lake dynamics on the Tuktoyaktuk Coastal Plain, Northwest Territories, Canada since 1985 |
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| Author | Olthof, I; Fraser, R H ; Schmitt, C |
| Source | Remote Sensing of Environment vol. 168, 2015 p. 194-204, https://doi.org/10.1016/j.rse.2015.07.001 |
| Image |  |
| Year | 2015 |
| Alt Series | Natural Resources Canada, Contribution Series 20181330 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®); html |
| Province | Northwest Territories |
| Subjects | geophysics; remote sensing |
| Program | Remote Sensing Science |
| Released | 2015 07 20 |
| Abstract | Several remote sensing studies have documented widespread thermokarst lake expansion in continuous permafrost regions of North America over the past few decades. Other studies have found no long-term
trends in water body extents, but large intra- and inter-annual changes driven by precipitation. These differences could be due to geographic variability in physical conditions (geology, climate, permafrost and hydrology) or in the data and methods
used to extract water bodies. This study tested water extraction methods over the Tuktoyaktuk Coastal Plain, Northwest Territories (NWT), Canada, based on the Landsat 5 shortwave infrared (SWIR) channel and validated them using water extents obtained
from 0.5m resolution orthophoto imagery. Methods included applying thresholds to generate binary land/water classifications, as well as deriving 30m water fractions from both linear unmixing and a new histogram breakpoint method. Results indicated
that the histogram breakpoint method outperformed other methods, underestimating overall water fraction by 0.26% and overestimating the number of pure 30m water pixels by 0.66% compared to water fractions calculated from orthophotos. The breakpoint
method was then applied to a stack of 17 near peak-of-season Landsat 5 and Landsat 7 images acquired between July 4 and August 18 from 1985 to 2011 to create a water fraction time-series for examining both trends and inter-annual variation in water
extent. Results showed an overall expansion of lake area along margins by 55km2 with isolated lakes experiencing rapid drainage totalling 15km2, leading to a net water area increase of 40km2 over the 26-year period. |
| Summary | (Plain Language Summary, not published)
Lakes in permafrost regions of Canada's western Arctic are changing due to climate warming. These changes are important for municipal water supply,
wildlife and climate change due to lake carbon and methane emissions. We developed a new water extraction method from Landsat and compared it to more traditional methods already being employed. As this new method was better able to depict water in
the study region of the Tuktoyaktuk Peninsula, it was then applied to a time-series of Landsat images from 1985-2011. We noted overall expansion around lake margins with isolated lakes experiencing sudden drainage over a period of a few years. Rates
of change are compared to other studies in the literature and show that similar changes are occurring across much of the world's arctic. |
| GEOSCAN ID | 311684 |
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