On 7th February 2021 just before noon, news reports came in regarding a flash flood in Rishi Ganga/Dhauli Ganga River in Chamoli district of Uttarakhand state, India. This brief report puts forth the probable causes for this flash flood that has originated in the Nanda Devi Biosphere Reserve using geospatial datasets and techniques. Datasets obtained from MODIS, Sentinel-2B, SRTM, ICESat-2 and ERA5 have been effectively utilized to infer the details about this event. Slow drizzle to severe snowfall has been witnessed during 3rd to 6th February 2021 in various parts of the Himalayan region; even the Rishi Ganga witnessed a heavy snowfall during this time. Data acquired on 10th February shows a scar developed due to a landslide on the shoulder of Ronti Mountain that was situated on the western rim of the Nanda Devi sanctuary. There was a gradual rise in temperature on 7th February 2021 at the surroundings of Ronti Mountain that consequently led to a landslide. The landslide perpetuated a movement under the influence of gravity from ~5900 m to ~3900 m with a mass envelope of ~0.290 km² and a velocity of 198 m/s that may have taken ~20 seconds to hit the Ronti bank. Due to the virtue of heat energy generated during this process resulted in contributing huge moraine filled flood water, that has accelerated towards the downstream of Rishi Ganga River and there after Dhauli Ganga River. Elevation profiles from the ICESat-2 and satellite imageries confirm the pre-existing conditions of landslide that is inclusive of weathering and erosion that led to the unstable condition at transportation back-slope of the Ronti Mountain. The triggering factors that influenced this landslide event and related causes were investigated in this study and reported herewith.

Building heights play a vital role in the field of urban morphology and allied applications. Recently there is a push to retrieve building heights from the space borne sensors. NASA’s ice, cloud, and land elevation satellite-2 (ICESat-2) carries a laser altimeter on-board that produces geolocated photon events on various types of surfaces such as glaciers, oceans, land and canopy on Earth. In this article, heights of the sampled buildings in an urban area were estimated using ICESat-2 photon data. The elevation from the geolocated photons reflected from the surface (bare Earth) of adjacent sides of a building under investigation was considered as local datum; similarly, the elevation of the building is computed from the geolocated photons reflected from the building roof. These two elevation estimates were used to compute the height of the building. These heights were evaluated using the field measurements. The estimated building heights from the profiles of ICESat-2 data agree with the field measurements with an accuracy ranging from 8 to 17 cm and suggest the utility of using ICESat-2 data for urban studies, if accuracy tolerance is in the centimeter level, is acceptable.

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AbstractNASA’s new Earth-Observing satellite namely ICESat-2 estimates the elevation of ice sheets, glaciers, sea ice, land surface, and canopy with the help of photon counting ATLAS sensor on-board. Higher-level data products like ATL08 uses an iterative filtering approach of the signal photons for capturing canopy height and terrain height. This article provides results from the evaluation of best-fit elevation on land from ICESat-2 ATL08 data product with DGPS surveyed points. 40 points were surveyed for elevation in the arid region with different topographies of varied surface cover. Mean bias error computed from the best-fit elevation from ICESat-2 ATL08 data product and corresponding DGPS surveyed points is near close to zero for the segments created from strong beams. The conformity between these two sets of elevation values is better than 12 cm (RMSE) if we use the segments from strong beam for the topographic variations ranging from flat to almost flat type.