Hydrological experiment over Ganga River to validate hydraulic parameters within the swath of SWOT mission

River discharge is one of the important hydrological essential climate variable (ECV) that is a key for understanding the water cycle of the catchment contributing to the river behavior and prevention strategies for efficient water resources. Surface Water Ocean Topography (SWOT) mission is first of its kind to estimate river discharge exclusively from remotely sensed hydraulic data. The present study demonstrated potential of SWOT mission KaRin swath observations to estimate water surface elevations (WSE), river width and slope over Ganga River, India. A field campaign was carried out in synchronous with the SWOT satellite (track 10) overpass during the Cal-Val phase of the mission. More than 4000 kinematic observation were collected using DGPS to monitor spatial variability of the water stage within the 120 km of swath altimetry. The elevation profile over water surface were estimated and observed the variation in water level from 61 to 70 m with an average slope of 8.69 cm/km. Acoustic Doppler Current Profiler (ADCP) was also operated every 10 km along the river similar to the reach wise discharge product for calibration/validation purpose.. This study generated a reliable dataset to validate the SWOT observations along with the estimated river discharge data set of the Ganga River near Varanasi with the aim of enhancing the accuracy of swath altimeter products. SWOT pixel cloud (SWOT_L2_HR_PIXC) data from KaRIn instrument was processed during Cal-Val phase form Cycle 484 (April 8, 2023) to Cycle 502 (April 26, 2023). For delineating the water extent from the Level-2 PIXC dataset, we have made use of a high-resolution national wetland inventory and assessment database of 1:12500 scale, so that small tributaries and nearby wetlands can also be consider for accuracy assessments over smaller water bodies. The PIXC product contains only a small fraction of the pixels in the interferogram (mainly water pixels and pixels in floodplains) that was further processed to estimate the river hydraulic parameters such as river slope, water level, and other related parameters for each pixel. The generated water elevation maps were validated with GPS measured elevations and similar order of variation in the water levels was observed by SWOT mission, with root mean square error of the order of 25 cm. The SWOT derived river slope (8.89 cm/ Km) was also in good agreement with the GPS observations. We have further analyzed the science phase data close to the virtual station near Varanasi from January 2024 to November 2024. The average water stage was observed to nearly 67.53 meter with peak-to-peak variation of the order of 8 meters. The river width during this period was observed to be varying between 400-3000 meter. Initial results from swath altimetry measurements have added a new dimension in the field of land hydrology and are essential for understanding hydrological processes.