Optimal estimation of total precipitable water from INSAT‐3D/3DR Imagers

Abstract

AbstractTotal precipitable water (TPW) is an important parameter for weather prediction apart from study of the hydrological cycle and climate change. Presently, TPW is generated operationally from infrared sounders on board INSAT‐3D and 3DR. However, the Sounder provides observations at a coarser resolution of 10 km over a limited region of coverage, and takes about 60 min to scan the Indian landmass. The Imager, in contrast, provides observation over a larger geographical region (full disc) at the interval of 30 min and a finer spatial resolution of 4 km. To exploit this advantage, an optimal estimation (OE) technique has been attempted to retrieve TPW from thermal infrared split‐window observations of INSAT‐3D/3DR Imagers in clear‐sky conditions. Assessment of the retrieved TPW is carried out for data of one year over land and ocean regions, separately against the three independent reference TPW products, acquired from radiosondes, Special Sensor Microwave Imager Sounder (SSMIS) on board Defense Meteorological Satellite Program (DMSP) F17 satellite, and fifth‐generation European Centre for Medium‐Range Weather Forecasts ReAnalysis (ERA5). The validation analysis of the retrieved TPW over land against the radiosonde observations and ERA5 TPW products for the entire period shows a root‐mean‐square error (RMSE) of less than 6 mm. An RMSE of better than 4 mm is observed over ocean, when compared with the operational TPW products of the SSMIS and ERA5 TPW products. Moreover, the RMSE of the retrieved TPW shows consistency for each month that clearly implies the robustness of the developed algorithm. The developed algorithm has been proposed for operational implementation at the Meteorological and Oceanographic Data Archival and Dissemination Centre (MOSDAC) hosted by Space Applications Centre, Ahmedabad and India Meteorological Department (IMD), New Delhi, India.