Topographic Wetness Index raster - Land Cover Mapping, North Slope of the Arctic National Wildlife Refuge, Alaska, 2019
Description
"We obtained the 5 m Interferometric Synthetic Aperture Radar Digital Terrain Model (IFSAR DTM) tiles for the study area from https://elevation.alaska.gov/ and mosaicked the products into a single image. We aggregated the DTM to 30 m resolution to represent a more generalized landscape level, and also to allow fairly rapid calculation of more processing-intensive terrain metrics. We then calculated the Sage Topographic Wetness Index at 30 m resolution. This integrates the local slope and the upstream contributing terrain in a continuous metric representing the potential wetness.
The 'SAGA Wetness Index' is, as the name says, similar to the 'Topographic Wetness Index' (TWI), but it is based on a modified catchment area calculation ('Modified Catchment Area'), which does not think of the flow as very thin film. As result it predicts for cells situated in valley floors with a small vertical distance to a channel a more realistic, higher potential soil moisture compared to the standard TWI calculation."