Evapotranspiration

sample thumbnail of evaportranspiration image

Evapotranspiration (ET) is the combined term to describe the water loss occuring by the processes of evaporation and transpiration. For vegetated surfaces, its refers to the water consumed by plants over a period of time. Calculation of ET is typically based on the conservation of either energy or mass, or both. Computing ET requires the estimation and combination of two complicated estimations; the stomatal conductance of the vegetation to derive transpiration and evaporation from the ground surface.

The MOD16 ET algorithm runs on a daily basis, and temporally, the daily ET is the sum of ET from daytime and night. Vertically, ET is the sum of water vapor fluxes from soil evaporation, wet canopy evaporation and plant transpiration at dry canopy surface. Remote sensing has long been recognized as the most feasible means to provide spatially distributed regional ET information over land surfaces. Remotely sensed data, especially those from polar-orbiting satellites, provide temporally and spatially continuous information over vegetated surfaces useful for regional measurement and monitoring of surface biophysical variables affecting ET, including albedo, biome type and leaf area index (LAI).

MOD16, the global 8-day (MOD16A2) and annual (MOD16A3) terrestrial ecosystem Evapotranspiration (ET) dataset at 0.5 km spatial resolution over the 109.03 million km² global vegetated land areas designed for the MODIS sensor aboard the Aqua and Terra platforms. The MOD16 algorithm is based on the logic of the Penman-Monteith equation which uses daily meteorological reanalysis data and 8-day remotely sensed vegetation property dynamics from MODIS as inputs.