Relative Terrain Height DEM transform for the mid-Juruá region, Brazilian Amazon

The Relative Terrain Height (RTH) is a novel DEM transform that facilitates 1) minimizing regional terrain height differences when comparing elevations of distal floodplain features; 2) optimizing terrain data for input to image segmentation algorithms; and 3) delineating boundaries of terrain features such as floodplains, fluvial terraces, interfluvial flats, and hillslopes. An example of RTH is given for a 2° x 2° area including the mid-Juruá region of the Brazilian Amazon, derived from the Copernicus GLO-30 Digital Elevation Model (DEM), at a resolution of 30m. The transform is based on differencing versions of the input DEM at 30 m (the original resolution) and 3000 m (resampled again to 30 m). The resulting RTH layer reflects the height of a feature relative to its surroundings, while retaining the detail of the original DEM, and the transform can easily be produced using any image processing software. The RTH is provided in GeoTIFF format. The input data set used to produce the RTH data product was the Copernicus WorldDEM-30.

Methods
The Copernicus GLO-30 DEM (https://doi.org/10.5270/ESA-c5d3d65; obtained 2020-11-20) was downloaded for the region 3.5° - 6.5° S to 65.5° - 68.5° W, and transformed to the Universal Transverse Mercator projection (UTM Zone 19S) at 30 m resolution; a buffer of 0.5° was added from adjoining tiles to avoid creation of artifacts at the boundaries of the study region, which extends from  4° - 6° S to 66° - 68° W. The 30 m DEM was resampled to 3000 m pixels (i.e., by a factor of 100) using weighted average resampling, then resampled back to 30 m using cubic convolution resampling. The original 30 m layer and the twice-resampled layer were next co-registered, and the twice-resampled layer was subtracted from the original DEM. The resulting Relative Terrain Height (RTH) layer was then cropped to the original DEM tile extent.