Detection and Mapping of Cover Crops Using Sentinel-1 SAR Remote Sensing Data
Sami Najem, Nicolas Baghdadi, Hassan Bazzi, Nathalie Lalande, L. Bouchet
Abstract
Cover crops are intermediary crops planted in between two main cash crops. They play a role in limiting nitrate leaching into ground water. Currently, there is no database pertaining to cover crops despite their importance. The development period of cover crop is characterized by a dense cloud cover in Europe, which obstructs land surface monitoring using optical remote sensing. This study proposes a cover crops mapping method based on SAR (Synthetic Aperture Radar) remote sensing data from the Sentinel-1 (S1) constellation which is unaffected by weather conditions. Our method is based on the dynamics of the S1 backscattering coefficient at the plot level. Using a decision tree, we mapped cover crops. In the decision tree algorithm, filters were added to eliminate other crops that temporally intersect with the cover crop, namely wheat and rapeseed. The proposed decision tree proved effective in detecting existing cover crop plots as shown by the classification Recall values ranging between 83.5% and 95.0% and the high precision values ranging between 81.5% and 89.2%. Comparison with Random Forest classifier showed that our proposed method yielded better and more consistent results. The main limitations in the classification approach were weak cover crops, and residual vegetation. The results show that the developed approach, based on S1 time series, is capable of remotely monitoring cover crops, giving managers and decision makers the ability to follow farmers' work and ascertain if they are applying the recommended agricultural practices that promote sustainable land use and limit the contamination of groundwater.