Estimating cotton coefficients using multi-temporal remotely sensed images in Alar irrigated region,NW China

Irrigation is critical for oasis agriculture in Alar irrigated region, Northwestern China. The reference evapotranspiration (ET₀) estimation using a modified Penman-Monteith method recommended by FAO is a baseline for rational irrigation scheduling. Thus, crop coefficients (K_c) were estimated using a ratio between reference and observed evapotranspiration. Then, we analyzed the relationship between temporal crop coefficients (K_c) and synchronized normalized difference vegetation index (NDVI) derived from multi-temporal remotely sensed images. The results showed that reference evapotranspiration increased from spring to summer hereafter decreased gradually to winter with the peak of ET₀ ranging from 8 to 9 mm/day. A closely linear relation between NDVI and K_c of cotton was finally acquired with a coefficient of determination of 0.94. An acceptable accuracy of this model by comparing observed and simulated evapotranspiration illustrated the credibility of this model. This paper provides a scientific approach to estimate regional crop coefficient and evapotranspiration.