Abstract:Rapid acquisition of crop coefficient Kc is the key to estimation of field evapotranspiration (ET), in order to study the feasibility and applicability of unmanned aerial vehicle (UAV) multispectral remote sensing in estimation of maize crop coefficient, based on the data of field maize in experimental station, soil and meteorology in Zhaojun Town, Dalate Qi, Inner Mongolia in 2017, by using meteorological factors and crop canopy cover to correct dual crop coefficient method at different growth stages and different water stresses. The multispectral (blue, green, red, red edge, near IR, 475~840nm) images from UAV were used to calculate vegetation indices (normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), enhanced vegetation index (EVI), simple ratio (SR) and green normalized difference vegetation index (GNDVI), visible atmospherically resistant index (VARI)) of maize in different growth stages (rapid growth stage, mid-growth stage and late growth stage). Thus the model relation of VIs and crop coefficient Kc could be established, and the effect of water stress on it was studied. Results demonstrated that maize growth period and water stress were two important factors influencing the VIs-Kc model. The correlation between VIs and Kc in different growth stages was different: under full irrigation condition, the correlation of VIs-Kc model in the rapid growth stage (R2 was 0.7312~0.9401, p<0.05, n=25) was different with the correlation of VIs-Kc model from mid to late growth stage (R2 was 0.2765~0.3732，p<0.05，n=40);under water stress condition, the correlation of VIs-Kc model in the rapid growth stage (R2 was 0.0002~0.0830, p<0.05, n=25) was different with the correlation of VIs-Kc model from mid to late growth stage (R2 was 0.3362~0.8487，p<0.05，n=40). Water stress had a significant effect on the correlation of VIs-Kc model: in the rapid growth stage, the correlation of VIs-Kc model for full irrigation maize (the maximum value of R2 was 0.9401) was better than the correlation for water stress maize (the maximum value of R2 was 0.0830);from mid to late growth stage, the correlation of VIs-Kc model for full irrigation maize (the maximum value of R2 was 0.3732) was worse than the correlation for water stress maize (the maximum value of R2 was 0.8487). The correlation of part of VIs and crop coefficient Kc was good;the descending order of correlation of VIs-Kc model for full irrigated maize in the rapid growth stage was SR, EVI, VARI, GNDVI and SAVI;the descending order of correlation of the VIs-Kc model for water stress maize from mid to late growth stage was SR, GNDVI, VARI, NDVI, SAVI and EVI;the correlation of SR and crop coefficient Kc was the best. Estimation of Kc based on UAV multispectral technology was feasible.
