REVIEW ARTICLES CURRENT SCIENCE, VOL. 123, NO. 7, 10 OCTOBER 2022 844 *For correspondence. (e-mail: megochasie@gmail.com) Application of GNSS-supported static terrestrial lidar in mapping landslide processes in the Himalaya Megotsohe Chasie*, P. K. Theophilus, Akshaya Kumar Mishra, Saibal Ghosh and Shib Kanta Das Geohazards Research and Management Centre, Geological Survey of India, Kolkata 700 091, India Site-specific topographic survey of 15 landslides in the four mountainous states of India, namely Uttarakhand, Jammu & Kashmir, Sikkim and Nagaland, was carried out through a terrestrial laser scanner campaign. The versatility of the lidar instrument in topographic sur- veys and its advantages over conventional survey prac- tices are highlighted. The effective use of the static terrestrial lidar in the rapid characterization and hazard assessment of landslides in this study is presented for adoption as a meaningful hazard assessment strategy in the hilly terrains. Keywords: Hazard assessment, hilly terrain, landslide, terrestrial lidar, topographic survey. THE basic requirement for any site-specific landslide ana- lysis is the availability of a topographic basemap of suita- ble accuracy at the desired scale. It enables mapping, plotting and representing all geological and non-geo- logical features on the slope under study. Often, the pri- mary predicament lies in the availability or time-bound generation of basemaps for such large-scale studies. In the Indian context, conventional survey methods using total station (TS) instruments to generate basemaps are com- mon, particularly for large-scale studies. However, such surveys are time-consuming and labour-intensive in terms of data acquisition, often compelling the operator to set-up and work from several datums 1 . Further, the presence of unfavourable site conditions like vegetation cover can lead to acquisition of less data points, thereby flattening subtle topographic features that may be crucial for accurate char- acterization of the slope 2 . The rapid development of light detection and ranging (lidar) technology, a three-dimensional remote sensing technique, during the past two decades has drastically im- proved the way we perceive and model the earth’s surface processes 3–5 . In this technique, the earth’s surface is scanned by laser scanners mounted over fixed or mobile platforms, including drones/unmanned aerial vehicles (UAVs), heli- copters, etc. to enable quick, 3D data capturing based on the project requirements. The terrestrial laser scanner (TLS) is one such ground-based survey instrument working on lidar technology, where a laser beam (pulse or continuous wave) is transmitted onto a surface and the returning signal is recorded for distance measurement. TLS can be fixed/ mounted on a tripod, in which case the platform is static/ stationary, or can be vehicle-mounted for a dynamic/mov- ing platform. This relief imaging by the scanner is used to extract very accurate digital elevation models (DEMs). A DEM is the digital representation of the topography/land surface elevation with respect to a given reference datum. During the last two decades, the use of DEM and its deri- vatives for determining terrain or morphometric attributes (slope, aspect, curvature, elevation, etc.) has provided more efficient ways for detailed landscape studies of land- slides 6–10 . Acquisition of multi-temporal datasets through repeated laser scanning has been exploited by various wor- kers for producing a DEM of difference (DoD) that allows for quantification of volumes and ground displacement changes 9,11–15 , and for monitoring of slopes 16–18 . Targeted laser scanning on exposed rock slopes to characterize rock discontinuities has also been carried out 19–23 . However, the potential of the technology and utility of the TLS output data, i.e. the 3D point cloud, the high-resolu- tion digital elevation model (HRDEM) and its derivative products in landslide studies are yet to be fully exercised/ adopted in a country like India, having 12.6% of its land mass (about 0.42 million km 2 ) susceptible to landslides (www.gsi.gov.in/webcenter/portal/OCBIS/pageGeoInfo/page- LANDSLIDEHAZRD?). Since the use of lidar-derived data- sets in detailed landslide studies is still in the evolving stage, this study showcases the benefits of the technology and versatility of the static terrestrial lidar instrument in site-specific topographic surveys for maximum exploitation of the state-of-the-art devices by the Indian geoscientific community. Study sites and nature of work Site-specific topographic surveys using the ground-based static lidar were carried out for 15 landslides distributed in four mountainous states of India, namely Uttarakhand, Jammu & Kashmir (J&K), Sikkim and Nagaland (Figure 1), where the first three states are physiographically located