Water vapor study using MODIS and GPS data at 64 continuous GPS stations (2002-2017) in indian subcontinent

摘要

Precipitable Water Vapor (PWV) is estimated using MODIS (Moderate Resolution Imaging Spectro-radio-meter) Terra level 3 data with daily resolution i. e MOD08_D3 at 64 cGPS (continuous Global Positioning System) stations spatially spread over Indian subcontinent between geodetic latitude 5 degrees to 35 degrees N and geodetic longitude of 70 degrees to 96 degrees E. MODIS-PWV is compared with GPS-PWV estimated at these cGPS stations to check the validity of water vapor retrieved from MODIS data in Indian subcontinent. Correlation coefficient (R-2) between daily values of MODIS and GPS water vapor is above 0.9 with RMSE (root mean square error) of 2-5 mm for 22 cGPS in peninsular India, above 0.9 with RMSE of 3-6 mm for 5 cGPS in northeast India and above 0.8 with RMSE of 1-9 mm for 26 cGPS in Himalayas. PWV time series at all the cGPS stations indicated distinct seasonal cycle for both MODIS and GPS PWV with high RMSE (similar to 6 nun) in wet months and low RMSE (similar to 3 mm) during dry months. Taking advantage of broad spatial spread of stations and long span of data, model for spatial variability of GPS-PWV for Indian subcontinent is proposed. Inter-annual and seasonal variability of GPS-PWV is discussed in detail for peninsular India, northeast India and Himalayas.