Derivation and validation of harvest index for winter wheat using MODIS NDVI data and ground measurements

In order to obtain the spatial information of winter wheat harvest index (HI) at regional scale, according to the definition of crop harvest index, depending on MODIS-NDVI time-series images to calculate accumulated NDVI at stage of after anthesis and before anthesis, the authors structured the parameter HI_NDVI-SUM which meant the ratio of accumulated 10-day NDVI at stages of after anthesis to accumulated 10-day NDVI at stages of before anthesis. Then, the relationship between the parameter HI_NDVI-SUM and the field measured HI of winter wheat was established. Finally, the authors used this relationship to get the spatial crop harvest index information. After validation of retrieved HI, it was shown that the accuracy of the retrieved HI of winter wheat was high and satisfied at large scale. The mean relative error of retrieved HI of winter wheat was only 2.40% and RMSE was only 0.02. It was proved that the method of structuring parameters of HI_NDVI-SUM and extracting harvest index for winter wheat based on NDVI time-series images was reasonable and feasible.