Abstract
We developed an automated approach for mapping persistent ice and snow cover (glaciers and perennial snowfields) from Landsat TM and ETM+ data across a variety of topography, glacier types, and climatic conditions at high latitudes (above ~65°N). Our approach exploits all available Landsat scenes acquired during the late summer (1 August–15 September) over a multi-year period and employs an automated cloud masking algorithm optimized for snow and ice covered mountainous environments. Pixels from individual Landsat scenes were classified as snow/ice covered or snow/ice free based on the Normalized Difference Snow Index (NDSI), and pixels consistently identified as snow/ice covered over a five-year period were classified as persistent ice and snow cover. The same NDSI and ratio of snow/ice-covered days to total days thresholds applied consistently across eight study regions resulted in persistent ice and snow cover maps that agreed closely in most areas with glacier area mapped for the Randolph Glacier Inventory (RGI), with a mean accuracy (agreement with the RGI) of 0.96, a mean precision (user’s accuracy of the snow/ice cover class) of 0.92, a mean recall (producer’s accuracy of the snow/ice cover class) of 0.86, and a mean F-score (a measure that considers both precision and recall) of 0.88. We also compared results from our approach to glacier area mapped from high spatial resolution imagery at four study regions and found similar results. Accuracy was lowest in regions with substantial areas of debris-covered glacier ice, suggesting that manual editing would still be required in these regions to achieve reasonable results. The similarity of our results to those from the RGI as well as glacier area mapped from high spatial resolution imagery suggests it should be possible to apply this approach across large regions to produce updated 30-m resolution maps of persistent ice and snow cover. In the short term, automated PISC maps can be used to rapidly identify areas where substantial changes in glacier area have occurred since the most recent conventional glacier inventories, highlighting areas where updated inventories are most urgently needed. From a longer term perspective, the automated production of PISC maps represents an important step toward fully automated glacier extent monitoring using Landsat or similar sensors.
Highlights
Glaciers have been identified as one of the most sensitive indicators of changes in climate [1,2] and have been identified as an essential climate variable that should be monitored globally [3]
Our results suggest that a standardized approach where pixels with Fraction of Days with Ice/Snow Cover (fDISC) values >0.8 are classified as persistent ice and snow cover (PISC) should work well across much of the northern high latitude regions
We demonstrate the feasibility of accurate monitoring of debris-free PISC across the northern high latitudes using automated processing of Landsat TM and ETM+ data that does not require manual intervention from an image analyst at any point in the processing chain
Summary
Glaciers have been identified as one of the most sensitive indicators of changes in climate [1,2] and have been identified as an essential climate variable that should be monitored globally [3]. While the presence of exposed ice at the end of the melt season allows most glaciers to be positively identified under the right conditions, smaller glaciers cannot always be reliably distinguished from perennial snow cover patches. The challenge of discriminating between perennial snow cover patches and glaciers is confounded by the lack of satellite imagery acquired under ideal conditions when the maximum amount of ice is exposed. Even high quality glacier inventories created by image analysts may include some large perennial snow cover patches or omit some small glaciers. We present a relatively simple automated approach designed to map glaciers that is likely to include a larger amount of perennial and consistently late lying seasonal snow cover patches than would be included in more traditional approaches. Our intent is to map glaciers, we refer to the automated maps produced by the approach we describe as persistent ice and snow cover (PISC) maps, acknowledging that some perennial snow cover and late lying seasonal snow cover may be included
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