This dataset was created by USGS and is being hosted by US EPA to support research and online mapping activities related to EnviroAtlas. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the contiguous United States. The dataset is available as downloadable data (https://edg.epa.gov/data/Public/ORD/EnviroAtlas) or as an EnviroAtlas map service. Additional descriptive information about each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).

The original raster dataset has additional categories to differentiate between permafrost probability areas and other land cover categories. In the USGS raster, values range from 0 to 105, with values above 100 representing the following: 101 = open water; 102 = perennial ice/snow; 103 = developed; 104 = barren, and; 105 = cultivated areas. These values has been modified by the EnviroAtlas team to change values above 100 to "-1" to produce a dataset with modeled likelihood values ranging from 0 to 100 only.

Abstract: Pastick et al., 2015 : "This medium resolution (i.e. 30-m pixels) spatial dataset provides an estimate of the occurrence of near-surface (within 1 m of the ground surface) permafrost in Alaska. The dataset was developed using a decision-tree model that statistically and spatially extended late-season field observations (n ~ 17,000) using remotely sensed imagery, climatic data, and thematic maps of a wide range of surface and subsurface biophysical characteristics. To circumvent the use of seasonal frost observations, only thaw-depth measurements taken during late-season months (late July to mid-September) or measurements designated to have no near-surface (within 1m) permafrost were used for model calibration and validation. Individual pixel values represent the probability of encountering near-surface permafrost (i.e. 0 to 100 %), as derived from a tree ensemble model, and pixel values greater than 100 correspond to masked land cover types (i.e. 101 = open water; 102 = perennial ice/snow; 103 = developed; 104 = barren, and; 105 = cultivated areas) as defined by the 2001 National Land Cover Database. Decision tree models and resultant maps were tested using independent field observations and f-fold cross validations, which indicated that the map product has an overall accuracy of approximately 85 % when using a probability threshold of 50 % (i.e. less than 50 % = near-surface permafrost absent; greater than or equal to 50 % = near-surface permafrost present)"

Pastick, N. J., Jorgenson, M. T., Wylie, B. K., Nield, S. J., Johnson, K. D., & Finley, A. O. (2015). Distribution of near-surface permafrost in Alaska: Estimates of present and future conditions. Remote Sensing of Environment, 168, 301-315. https://doi.org/10.1016/j.rse.2015.07.019