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Estimating crop water use from remotely sensed NDVI, crop models, and reference ET

Date

2007-10

Authors

Trout, Thomas J., author
Johnson, Lee F., author
U.S. Committee on Irrigation and Drainage, publisher

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Abstract

Crop water use can be estimated from reference evapotranspiration, ETo, calculated from weather station data, and estimated crop coefficients, Kc. However, because Kc varies with crop growth rate, planting density, and management practices, generic Kc curves often don't match actual crop water use. Recent studies have shown that basal crop coefficients, Kcb, are related to crop light interception or canopy cover; and that canopy cover can be estimated for a wide variety of crops from remotely sensed observations of the normalized difference vegetation index, NDVI. Combined, these relationships could provide good estimates of Kcb from satellite or aerial data for a wide variety of crops over large areas. When combined with ground based ETo measurements and general knowledge of irrigation methods, crop water use can be estimated for individual fields and for large regions. Because NDVI data are generally available only intermittently during the season, simple plant growth models can be used to interpolate canopy cover between vegetation index measurements, and to extrapolate crop canopy cover into the future. This system may improve estimates of crop water use compared to traditional FAO-56 methods and provides an alternative to remotely-sensed estimates of ET that use thermal data with surface energy balance calculations.

Description

Presented at the Role of irrigation and drainage in a sustainable future: USCID fourth international conference on irrigation and drainage on October 3-6, 2007 in Sacramento, California.

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