Reconstruction of the lost Saraswati river course and its associated palaeochannels using multi-resolution SAR and MSS images in the northwestern desertic plains of Rajasthan, India

The lost Saraswati River offers a significant challenge for geomorphologists and archaeologists. It is believed that the river used to flow through the present-day Thar Desert during the Vedic age. It desiccated between ∼7000 and ∼1200 BC due to tectonic and climatic changes, leaving behind palaeochannels and playas in northwestern Rajasthan. This study aims to delineate the ancient Saraswati River and its associated palaeochannels using multi-sensor satellite data, including SAR (Sentinel-1A, ALOS PALSAR), multispectral (Sentinel-2A), and DEM. Multiple fusion algorithms (IHS, GS, PCA, Wavelet, and Ehlers) were used to fuse SAR and optical data, enhancing the visibility of the river course and palaeochannels. Various image indices assessing surface moisture and vegetation patterns further helped in palaeochannel detection. Among the fused images, the IHS, GS, and PCA techniques, combining Sentinel-2 and ALOS PALSAR data, were found to be the most effective in highlighting palaeochannels. Further, image indices such as NDVI, NDWI and NDMI led to confirm palaeochannels and the old river course by showing linearly oriented vegetation and soil moisture. The study successfully traced two major palaeo-courses of the Saraswati River, originating from the Ghaggar River near Anupgarh and flowing through Beriyawali, Bahla, Tanot, and Jaisalmer before emptying into the Great Rann of Kutch. Additionally, three major palaeo-drainage systems of the Saraswati River could be delineated. Moreover, the association of the Harappan archaeological sites distribution along with the delineated Saraswati River course and its paleochannels, evidence from the historical maps, and bore-well drilling data (groundwater levels and lithologs) also confirm the results of this study.