Synergistic use of SWOT with other water-focused satellite missions (GRACE-FO) to understand the change in the total water storage for Ganga-Brahmaputra River basins

Principle Investigator: Shard Chander (Space Applications Centre, ISRO, India)

Co-Investigator(s): Ritesh Agarwal, Amit Dubey, Praveen Kumar Gupta, Rashmi Sharma

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River discharge and lake/reservoir surface water storage are two critical elements of land surface hydrology. Adequate knowledge of river flow or discharge is still missing in most of the global river basins that sustain human needs. Imaging altimetry promises a leap forward for land surface-water hydrology in much the same way that satellite radar altimetry liberated physical oceanography from a limited collection of tide gauges (Smith and Pavelsky, 2009). SWOT is a next generation mission to map water elevation for studying Earth. Some of the scientific questions from a hydrological perspective where SWOT will be useful are the spatial and temporal variation in the availability of freshwater resources. Single pass, single platform interferometric synthetic aperture radar (InSAR) with 8 mm wavelength, will improve the resolution one or two order to meet the requirement of hydrological applications.

The research activity will focus on the “Utilization of swath altimetry dataset for hydrological applications”. The current state of art satellite sensors like SWOT, GRACE/GRACE-FO etc. along with present generation on-board altimeter sensors such as Sentinel-3A/3B and Sentinel-6 will be utilized for monitoring the long term variation in the water resource over Ganga river basin. GRACE/ GRACE-FO mission that measures changes in gravity, from which we infer the mass of water and its change is also of great relevance to hydrology and total water storage in general. GRACE has proven valuable for groundwater monitoring whereas SWOT, on the other hand, will add the surface water component. Both dataset will be used synergistically for monitoring total water storage variation. There are mainly three sources of error that may have impact on the derived river discharge, i.e. error due to satellite, due to atmospheric delays (wet troposphere, ionosphere, etc.) and errors associated with ancillary dataset such as river hydraulics. Efforts will be made for the latter two error sources. Inter-annual and inter-seasonal dynamics of total water storage will be studied over the Ganga basin. Such an updated database of water storage volume would help us to manage our fresh water reserves more efficiently.