Abstract

CASTANEDA-IBANEZ, Carlos R. et al. Estimation of crop coefficients through remote sensing in the Río Yaqui irrigation district, Sonora, México. Agrociencia [online]. 2015, vol.49, n.2, pp.221-232. ISSN 2521-9766.

Traditional estimations of evapotranspiration (ET) are based on the crop coefficient (K_c). This can be disadvantageous when precise estimations of crop water uptake are required in the Irrigation Districts. Using satellite images, it is possible to estimate vegetation indexes (VI), such as the Normalized Difference Vegetation Index (NDVI) and the Soil Adjusted Vegetation Index (SAVI). These indexes enable monitoring crop development and estimating precisely spatial and temporal K_c variability. The objective of this study was to validate the use of VI to estimate K_c and ET of wheat (Triticum aestivum) in the Río Yaqui Irrigation District, Sonora, Mexico. Validation was carried out with eight images from the sensors TM and ETM+ of the LANDSAT 5 and 7 satellites and measurements of turbulent flux with the Eddy Covariance (EC) technique for the year 2008. ET estimated from VI and measurement with EC showed a high degree of correspondence. For the eight images, the square root of the Root Mean Square Error (RMSE) was 0.69 mm d^-1, the Mean Absolute Error (MAE) 0.62 mm d^-1, the index of agreement (d) 0.91 for NDVI and RMSE of 0.64 mm d^-1, MAE of 0.57 and an index of agreement of 0.92 for SAVI in daily estimations. It is thus concluded that VI allow to estimate spatial and temporal variability of the K_c and ET with precision in extensive agricultural regions.

Keywords : Triticum aestivum; evapotranspiration; crop coefficients; satellite images; vegetation indexes; remote sensors.