2.2.4. Validation of the Model

In addition to visual examination, the estimated cropping intensity was validated by using the Sentinel-2 derived cropping intensity data, MCD12Q2 product, GCI dataset and GCI30 dataset as references.

The accuracy of the model output was evaluated using the coefficient of determination R2, root mean square error (RMSE) of the linear fitting with respect to the reference data.

The validation was conducted at grid level and county level, respectively. On grid level, both the modeled result and the reference data were aggregated to 2 km fractural images by summarizing the values within each grid. On county level, zonal statistics were used to summarize the data to county level for those complete counties in the research area.

The software packages used in this research for constructing the feature space and the model validation were ENVI (ENVI version 4.8, Exelis Visual Information Solutions, Boulder, CO, USA) and MATLAB (MATLAB 2018a, The MathWorks, Inc., Natick, MA, USA).

#### **3. Results**
