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Integrated precipitable water vapor (PWV) retrieved from Moderate Resolution Imaging Spectro-radiometer (MODIS) in near-infrared channels is examined with the PWV estimated from the Global Positioning System (GPS) data and measured surface temperature and pressure values over Hanle, located at a high-altitude (∼4500 m) trans-Himalayan region. Since the accuracy of MODIS derived PWV over the large elevated topography of the region is not well studied, the present work focus on the validation of MODIS PWV using the GPS data during 2005–2012. The study reveals that MODIS PWV compares well with the GPS PWV data with bias −0.018 cm, root mean square error (RMSE) 0.137 cm and coefficient of determination ( R 2 ) 0.91. The two types of data products are compared on short (daily) and long temporal (monthly-seasonal) scales in order to evaluate the seasonal dependence of PWV. The peak values of PWV from MODIS and GPS data at the site varied from 1.7 to 2.05 cm and 1.2 to 1.4 cm as the daily and the monthly means, respectively, which occurred during August. However, the seasonal peak of PWV occurred during summer as 0.88 and 0.97 cm for MODIS and GPS data, respectively. The present study noticed that about 85% of the total PWV estimated from MODIS as well as GPS data lies below 1.0 cm over the site. The seasonal study of PWV reveals that MODIS data is found to be underestimating the PWV when compared to GPS data with bias −0.095 cm and RMSE 0.215 cm particularly during summer. This is due to dry and high-altitude terrain of Hanle particularly during summer months. However, there are marginal differences (bias varied from 0.007 to 0.017 cm) during the remaining seasons and seasonally R 2 varies from 0.62 to 0.87. GPS PWV exhibits distinct diurnal cycle with minimum in morning as well as in night and peak in the late afternoon (16–18 h) irrespective of the seasons. However, the diurnal cycle is very prominent during summer than the rest of the seasons. [ABSTRACT FROM AUTHOR]

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° to 35° N and geodetic longitude of 70° to 96° 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 (R2) 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 (~6 mm) in wet months and low RMSE (~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. • Validation of MODIS-PWV using long data span at 64cGPS sites for Indian region. • MODIS-PWV has high RMSE, bias for coastal, islands and varying topography regions. • MODIS data fails to capture the seasonal variability of PWV for Indian sub-continent. • Spatial variability function of GPS-PWV is given for Indian Sub-continent. • Relation between the seasonal variability of PWV and temperature variation is given. [ABSTRACT FROM AUTHOR]