ESTIMATING CROP WATER USE FROM REMOTELY SENSED NDVI, CROP MODELS, AND REFERENCE ET

摘要

Crop water use can be estimated from reference evapotranspiration, ETo, calculated fromrnweather station data, and estimated crop coefficients, Kc. However, because Kc varies with croprngrowth rate, planting density, and management practices, generic Kc curves often don't matchrnactual crop water use. Recent studies have shown that basal crop coefficients, Kcb, are related torncrop light interception or canopy cover; and that canopy cover can be estimated for a widernvariety of crops from remotely sensed observations of the normalized difference vegetationrnindex, NDVI. Combined, these relationships could provide good estimates of Kcb from satelliternor aerial data for a wide variety of crops over large areas. When combined with ground basedrnETo measurements and general knowledge of irrigation methods, crop water use can bernestimated for individual fields and for large regions. Because NDVI data are generally availablernonly intermittently during the season, simple plant growth models can be used to interpolaterncanopy cover between vegetation index measurements, and to extrapolate crop canopy cover intornthe future. This system may improve estimates of crop water use compared to traditional FAO-rn56 methods and provides an alternative to remotely-sensed estimates of ET that use thermal datarnwith surface energy balance calculations.