RESEARCH
Research Interests
Remote Sensing, Synthetic aperture radar Interferometry (InSAR),Geographical Information Systems (GIS), Earth observation Glaciology, Land deformation
Glacier elevation and mass changes in Himalaya-Karakoram
Our work in high-mountain Asia is based on two radar digital elevation models; Shuttle Radar Topography Mission (SRTM) from 2000 and TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) from 2012.
Our observed glacier elevation and mass changes indicate a regional heterogeneity in the Himalaya-Karakoram with maximum changes in Lahaul-Spiti and Jammu and Kashmir West (Himalaya) regions and comparatively lesser changes in Jammu and Kashmir East (Karakoram) region. This is inline with many other studies, based on a variety of satellite remote sensing data, which also show that the glaciers in Karakoram, Kunlun Shan and eastern Pamir maintain mass balance since the 1960s. This is anomalous to rest of high-mountain Asia where glaciers have been losing mass.
With our spatially detailed observations, thanks to radar observations unaffected from cloud cover, adverse weather situations or day/light conditions, we indicated the role of supraglacial debris, lakes and ice cliffs, which influence the glacier response to climate change.
Updated from Vijay and Braun (2016,2018)
Ice dynamics of tide-water glaciers
We have been observing seasonal ice dynamics of tidewater glaciers in Alaska and Greenland using several satellite remote sensing (mainly radar) missions.
1. Columbia Glacier, Alaska: The German Space Agency (DLR) launched a twin X-band radar mission, called TanDEM-X, in 2010 and since then the mission has acquired aplenty of bistatic interferometric data around the globe. The bistatic data comprise simultaneously acquired two SAR images as a result of active and passive constellation of the twin satellites. One of them sends the radar signal towards Earth and both of them receive the signal backscattered from Earth. The mission acquire data every 11 days for several super test sites including Columbia Glacier, Alaska. We observed 11 days of ice velocity, surface elevation, ice front positions and radar backscatter obtained after processing TanDEM-X data and combined them with daily air temperatures and precipitation. We found detailed signals about how seasonal ice velocity of the main branch of Columbia Glacier is primarily driven by surface melt induced changes in the subglacial hydrology. Some specific events, where abrupt velocity changes are coincident with ice frontal retreat, which can be explained by changes in the driving and resistive stress. These phenomena were most seen at the west branch (now called Post Glacier).
Columbia Glacier, Alaska (US)
2. Greenland: Greenland has many glaciers that terminate to the ocean - often called as tide-water glaciers. The European Space Agency (ESA) launched Sentinel-1 radar mission in 2014 consisting of one C-band radar sensor that has been consistently capturing the land surface of Earth with great details. The frequency has doubled after ESA launched a second planned satellite in 2016. This made it possible to capture Greenland's surface with daily to sub-weekly time scales throughout the year. Since the data is publicly available without any restrictions, many global initiatives have taken place that use Sentinel-1 radar data to monitor ice flow of Greenland glaciers. These initiatives include NASA's MEaSUREs program and GEUS (Geological Survey of Greenland and Denmark) PROMICE program.
We made use of PROMICE ice velocity products to study seasonal ice velocity of Greenland glaciers and found relationships between ice flow and surface melt conditions. However, the glaciers respond differently to surface melting conditions -- some glaciers speedup with the onset of surface melt and attain maximum velocity after couple of weeks followed by slowdown. Other set of glaciers show comparable velocities in late-winters and spring or slight speedup with the melt onset. They slowdown during most of the melt season. These contrasting velocity fluctuations are mostly likely linked with the subglacial hydrology. Our current work focuses to find more details on this relationship.
We also found that the ice flow of some of the glaciers correlated well with the frontal changes.