Use of Remote Sensing to Generate Crop Coefficient and Estimate Actual Crop Evapotranspiration

Abstract. Irrigation water is limited in many regions of the world. Accurate estimation of crop water requirements allows proper irrigation management and water conservation. A method used for estimating crop water requirement is the use of reference evapotranspiration (ETo) and crop coefficient (K_c). The objectives of this study were to generate K_c and estimate actual evapotranspiration (ETc) in forage crops using remote sensing in Northern Mexico. Monthly clear sky imagery from Landsat 5 (path/row 30/42) from March to November 2011 were used. The Normalized Difference Vegetation Index (NDVI) was calculated from reflectance of the red and near infrared bands. The relationship between NDVI derived from satellite images and K_c from literature was established. This relationship was used to create new K_c values for corn and alfalfa using additional overpass dates. The actual ET was estimated using new regional K_c and reference ET, which was estimated utilizing meteorological information from local agro-climatic stations. Results showed high coefficient of determination (r²) (0.97) between NDVI and K_c FAO-56, this relationship helped to generate new K_c curves for forage crops. The output of K_c values were multiplied by reference ET to estimate actual ET. The estimated crop water consumption on actual ET were 476 mm ha^-1 for corn and 945 for alfalfa, saving 25 and 32% of irrigation water respectively. Remote sensing was a useful tool for generating local K_c and estimate accuracy of actual ET. Using this technology we can improve water management and conserve irrigation water.