Fig 1.
The study area ranges in latitude from 35.6444° to 39.0298° and in longitude from -79.6179° to -85.8093°. Geospatial data describing the study area and the ultimate model outputs are available to download at https://www.skytruth.org/mtr-data-files/.
Fig 2.
Example NDVI image and associated true color image.
These images from May 2014 show the area near Spurlockville, WV, and in particular the Hobet-21 mountaintop coal mine (38.08°, -81.95°). Darker colors in the NDVI image (A) indicate lower NDVI values. True color imagery (B) demonstrates that, in the visual spectrum, forested areas appear green whereas mined areas appear gray. Both images are derived from Landsat 8 top-of-atmosphere reflectance imagery and were processed in Earth Engine for visualization.
Fig 3.
Active mining, cumulative mining, and coal production over time.
“Active Mining” (A) means any land area detected by our model as likely mine for the given year; “Cumulative Mining” (B) is the non-duplicative summation of active mine area over time; this sum includes mine areas identified from pre-1976 through 1984 from the MTM2009 data (see above). “Newly-Mined Areas” (C) is the land area that was first converted into a mine in the given year. “Surface Coal Production” (D) data is from the Mine Safety and Health Administration [30] rather than our model; we present it here for comparison.
Fig 4.
Annual change in cumulative mining versus change in active mining.
“Active Mined Area” is any area per year where the maximum NDVI observed in that year was less than the NDVI threshold set per county per year. “Cumulative Area” is the summation of unique active mine area over time; if some location was identified as active mine in one year, its area would not be added again to the cumulative mining total in future years. Each 1 m2 of land in active mining is associated with 0.22 m2 of newly mined area.
Fig 5.
Yearly mine production versus active mine area, with and without a 5-year time lag.
Rates of coal production from surface coal mines in the region are compared to the scale of active mining estimated in the same year (red circles) and five years previously (black circles). There is no relationship when data are analyzed from the same year, but the amount of coal produced five years earlier explains 68% of the variance in active mining area (regression fit shown in blue with 95% confidence interval in gray).
Fig 6.
Ratio of active mine land per metric ton of coal produced over time.
Table 1.
Available processing scripts and data products for download.