Mapping wetlands of the Sundaban Delta and it's environs using ERS-1 SAR data

Wetlands play an important role in bio-geochemical cycling, flood control and recharging of aquifers. They serve as a major source and net sink of carbon and a potential site for aquaculture and the breeding of waterfowls. The wetlands of Sundarban and its adjoining areas support a variety of flora and fauna and they are currently being used for fish culture. Precise information of their nature, extent and spatial distribution is a pre-requisite for their optimal utilization. Being a coastal region, the cloud-free optical remote sensing data for the area is not very often available. Synthetic aperture radar, which has the ability to penetrate cloud, permits regular and repetitive observation of the wetlands. A study was made to evaluate the potential of the ERS-1 SAR data for delineating wetlands in part of the Sundarban delta and its adjoining areas of West Bengal. ERS-1 SAR data was analysed/interpreted in conjunction with optical data, i.e., Indian Remote Sensing Satellite (IRS-1B) data, acquired simultaneously or very close to the SAR data collection, collateral information and satellite overpass-synchronous ground truth. After filtering digital SAR data for removing speckles, wetlands were mapped through density slicing and using a parallelopiped algorithm. An effort was also made to correlate DN values of SAR data with various natural and cultural features of the terrain. The synergistic information contained in the SAR data was evaluated by digitally merging SAR data with the concurrent or near real-time IRS-1B LISS data. The false colour composite, thus prepared, was found to have an edge over either of the data sets in terms of the delineation of wetlands. The cloud penetration capability was also demonstrated through a data set comprising SAR and IRS-1B LISS-II data that were acquired on the same day virtually at the same time. Monitoring of wetlands using temporal SAR and optical data is being attempted.