Post-event SAR stereo DEMs (Umbra) for the 2026-08-26 Rasuwa (Langtang Lirung) ice-rock avalanche, Nepal

This record provides digital elevation models (DEMs) from post-event synthetic aperture radar (SAR) images following the 2026-08-26 ice-rock avalanche on the north flank of Langtang Lirung, Rasuwa District, Nepal. The DEMs were produced from Umbra spotlight SAR image pairs collected 2026-09-01 through 2026-09-13, with two complementary collection geometries. The record includes the five individual pair DEMs, a composite for each geometry, and a composite of both. All products are cloud-optimized GeoTIFFs in EPSG:32645 (WGS 84 / UTM zone 45N) with heights above the WGS 84 ellipsoid, posted at 8 m. The DEMs are co-registered to a common pre-event reference surface; users may wish to perform their own co-registration for their application. License: NASA CSDA Public Release license. Original Umbra spotlight SAR images (c) Umbra Lab Inc. 2026. 1. Products File suffixes: _dem single pair DEM; _ordered priority-ordered composite; _wmean weighted-mean composite; _hs hillshade; _ordered_source input dataset that supplies each pixel of the ordered composite (listed in _ordered_source_index.csv); _count number of inputs per pixel. Nodata is -9999 in elevation and count layers and 0 in hillshade and source layers. 00_*_preview.png files are quick-look figures. 1.1 Input images Six Umbra X-band spotlight images, geocoded ellipsoid-corrected (GEC) products at 1 m posting (0.25 m azimuth x 1 m range resolution, 4 azimuth looks), with rational polynomial coefficient (RPC) sensor models. Two geometries (look azimuth is from the target to the sensor): West-low: sensor west of the target, grazing angles 35-38°. East-high: sensor east of the target, grazing angles 50-68°. collect ID satellite acquired (UTC) geometry orbit look azimuth (°) grazing angle (°) squint (°) 166be78e-20fb-442f-8b6e-5c39ad21c805 UMBRA-09 2026-09-01 17:56:33 west-low ascending 276.1 34.8 15.2 38614c21-d2ce-4664-92c3-84f717d1fffd UMBRA-07 2026-09-02 03:32:40 east-high descending 91.8 68.2 9.3 6088b64e-a4a8-4feb-91df-033a847f72b2 UMBRA-07 2026-09-03 15:34:29 west-low ascending 277.7 35.7 16.4 f6a8babc-d620-44ca-9b97-035890b7a115 UMBRA-07 2026-09-09 04:04:53 west-low descending 278.9 37.5 5.6 26e19da8-a4e4-4c53-bffc-a30d7903b89d UMBRA-10 2026-09-11 05:51:40 east-high descending 71.9 50.3 28.6 8905845e-38b2-4dae-95cb-b9f3acfef0c9 UMBRA-10 2026-09-13 17:21:08 east-high ascending 64.6 57.2 12.2 1.2 Pair DEMs (rasuwa_post_umbra_pairs.zip) file geometry convergence angle (°) time between images (days) rasuwa_post_umbra-westlow_20260901T1756Z-20260909T0404Z_8m_dem_v1.0.tif west-low 15.7 7.4 rasuwa_post_umbra-westlow_20260903T1534Z-20260909T0404Z_8m_dem_v1.0.tif west-low 15.7 5.5 rasuwa_post_umbra-easthigh_20260902T0332Z-20260911T0551Z_8m_dem_v1.0.tif east-high 14.2 9.1 rasuwa_post_umbra-easthigh_20260902T0332Z-20260913T1721Z_8m_dem_v1.0.tif east-high 23.7 11.6 rasuwa_post_umbra-easthigh_20260911T0551Z-20260913T1721Z_8m_dem_v1.0.tif east-high 20.5 2.5 Convergence angle: median over interest-point matches, reported by ASP stereo from the RPC models. 1.3 Composites (rasuwa_post_umbra_composites.zip) rasuwa_post_umbra-westlow_20260901-20260909_8m_{ordered,wmean}_v1.0.tif rasuwa_post_umbra-easthigh_20260902-20260913_8m_{ordered,wmean}_v1.0.tif rasuwa_post_umbra_20260901-20260913_8m_{ordered,wmean}_v1.0.tif 2. Methods DEMs were generated with the NASA Ames Stereo Pipeline (ASP 3.8.0-alpha, 2026-08-20 build; Shean et al., 2016; Beyer et al., 2018), following the spotlight SAR radargrammetry workflow of Shean et al. (2025), using the RPC models and the ASP implementation of the More Global Matching correlation algorithm (MGM; Facciolo et al., 2015; asp_mgm, 9 x 9 px kernel). Output 2 m DEMs were created using the ASP point2dem and downsampled to 8 m using an incremental Gaussian downsampling to mitigate artifacts. Each DEM was co-registered by a translation to a common pre-event reference surface on stable ground, excluding surfaces that changed during and following the 2026-08-26 event. Composites were built with the ASP dem_mosaic as priority-ordered and weighted-mean mosaics, after filling holes of up to 1 ha within each input. 3. Known issues Steep, shadowed or texture-poor terrain has gaps and localized errors. 4. License and acknowledgments NASA CSDA Public Release license. Original Umbra spotlight SAR images (c) Umbra Lab Inc. 2026. This work utilized data made available through the NASA Commercial Satellite Data Acquisition (CSDA) Program. Thanks to Jordan Bell (NASA CSDA), Jane Zugarek (Umbra) and Paul Behrens (Umbra) for assistance with tasking and delivery. Funding: NASA award 80NSSC24K1633 (HiMAT-2B) and NASA award 80NSSC26K0856 (DSI24). Products were generated on a rapid disaster-response timeline and are provided without warranty. 5. Citation Shean, D. (2026). Post-event SAR stereo DEMs (Umbra) for the 2026-08-26 Rasuwa (Langtang Lirung) ice-rock avalanche, Nepal (v1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.22842744 References Facciolo, G., de Franchis, C., and Meinhardt, E. (2015). MGM: A significantly more global matching for stereovision. Proceedings of the British Machine Vision Conference (BMVC), 90.1-90.12. https://doi.org/10.5244/C.29.90 Beyer, R. A., Alexandrov, O., and McMichael, S. (2018). The Ames Stereo Pipeline: NASA's open source software for deriving and processing terrain data. Earth and Space Science, 5, 537-548. https://doi.org/10.1029/2018EA000409 Shean, D. E., Alexandrov, O., Moratto, Z. M., Smith, B. E., Joughin, I. R., Porter, C., and Morin, P. (2016). An automated, open-source pipeline for mass production of digital elevation models (DEMs) from very-high-resolution commercial stereo satellite imagery. ISPRS Journal of Photogrammetry and Remote Sensing, 116, 101-117. https://doi.org/10.1016/j.isprsjprs.2016.03.012 Shean, D., Alexandrov, O., Henderson, S., and Bhushan, S. (2025). An open-source radargrammetry pipeline for 3D terrain reconstruction using commercial SAR images. Joint Agency Commercial Imagery Evaluation (JACIE) Workshop, Reston, Virginia, 9 April 2025. https://calval.cr.usgs.gov/apps/sites/default/files/jacie/2025-Active-Sensors-David-Shean-University-of-Washington.pptx