Chamoli Disaster Post-event 2-m DEM Composite (February 10-11, 2021) and Difference Map

This “fine-quality” 2-m DEM composite was created using a combination of 5 cross-track stereo DEMs generated from 5 overlapping monoscopic Maxar/DigitalGlobe WorldView-2, WorldView-3 and GeoEye-1 images acquired on February 10, 2021 and February 11, 2021, and one DEM generated from 2 Pléiades-HR1B in-track stereo images acquired on February 10, 2021. This composite provides the first continuous DEM of primary areas affected by the February 7, 2021 event.

The 5 cross-track stereo DEMs were processed by the UW team using the NASA Ames Stereo Pipeline v2.6.2_post (Beyer et. al, 2018; build d7eb7c8) and a modified version of the methodology presented in Shean et al. (2016; 2020). Input images were orthorectified at native GSD using the 30-m Copernicus DEM (converted to ellipsoidal heights). See http://doi.org/10.5281/zenodo.4533679 for additional details on processing. Each output DEM (height above the WGS84 ellipsoid) was posted at 2.0 m with UTM 44N projection (EPSG:32644).

The Pléiades stereo DEM (Chamoli_2021-02-10_SGM/Chamoli_2021-02-10_DEM_4m.tif) was processed by the CNRS team using the NASA Ames Stereo Pipeline with SGM correlation algorithm. The output DEM (height above the WGS84 ellipsoid) was posted at 4.0 m with UTM 44N projection (EPSG:32644). For additional details on processing of the Pléiades DEM, see Deschamps-Berger et al. (2020).

Each DEM was co-registered to a filtered/masked version of the September 2015 Chamoli Disaster Pre-event 2-m DEM Composite (http://doi.org/10.5281/zenodo.4554647) using the demcoreg/dem_align.py utility (http://doi.org/10.5281/zenodo.3243481) with RGI glacier polygons and snow (Panchromatic top-of-atmosphere reflectance threshold of 0.4) masked. One cross-track DEM (WV02WV02_20210211_10300100B5B53500_10300100B5AB8400) with poor stereo geometry (convergence angle of 7.6°) required an additional planar correction, which was fit to masked/filtered DEM difference values. The Pléiades DEM required additional correction to remove along-track “jitter” artifacts. This was accomplished by computing median value for each row of the masked/filtered DEM difference map, smoothing the resulting 1D curve with a Savitzky–Golay filter (window length of 101 px, polynomial order 2), and removing from the full Pleiades DEM.

A per-pixel weighted mean DEM composite (*wmean.tif) was produced from the co-registered, filtered DEMs using the ASP dem_mosaic utility (https://stereopipeline.readthedocs.io/en/latest/tools/dem_mosaic.html). This approach uses a weighting scheme that favors spatially continuous coverage (as opposed to small clusters separated by nodata values). Due to the limited set of overlapping DEMs, several areas of the composite include values from a single input DEM