ENERGY BUDGET OVER SEMI-ARID AGRO-ECOSYSTEM USING SATELLITE DATA

摘要

Energy-water-carbon cycle is the central theme of biosphere-atmosphere interaction to understand the response and feedback processes in a climate system. The crop response in a semi-arid climate is frequently encountered by water scarcity due to maldistribution of rainfall or lack of irrigation water leading to low agricultural productivity. The characterization of water stress over large agriculture using thermal regime over crop surface in periodic manner throughout crop growth cycle is thus extremely important. Though, conventional measurements with Lysimeter keep record of field and soil specific water balances in root zone but cannot be extrapolated to larger area. The combination of optical band data in terms of albedo, NDVI threshold based emissivity and thermal band data in terms of Land Surface Temperature can represent evapotranspiration (ET) through energy balance approach over a spatial domain. Energy balance estimates derived from MODIS AQUA were validated with in situ attented and unattended observations for two wheat seasons, 2005 - 06 and 2006 - 07, within a 5km x 5km wheat growing region of Kheda district in Gujarat. Daily AQUA evapotranspiration estimates in terms of daytime latent heat fluxes were found to have root mean square error (RMSE) 29 Wm~(-2) (r velence 0.72) and 26 Wm~(-2) (r velence 0.8), respectively as compared to attended measurements during both the seasons. Correlation was substantially more and RMSE were less when estimates were compared with in situ measurements using Large Aperture Scintillometer (LAS) sensible heat fluxes.