Objectives  The key phenological information of oilseed rapeseed (Brassica napus L.) plays an important role in field management, viewing time prediction and yield estimation of the oilseed rape. It is also an important part of precision agriculture. Polarimetric synthetic aperture radar technology shows great potential in phenological phase identification with its all-weather monitoring capability and its sensitivity to the crop structural information.

  Methods  First, we identified the 5 phenological phases of the oilseed rape on the test area with 5 time series full-polarization Radarsat-2 data, which covers the whole growth period of the oilseed rape. 6 typical Stokes parameters are extracted and applied in the identification of oilseed rape phenological phases, the extracted Stokes parameters includ averaged intensity( g_0 ), normalized average intensity( g_0m ), averaged degree of polarization( \rho _m ), perimeter degree of zero orientation route( P_\mathrmd\mathrmo\mathrmr ), inclination degree of zero aperture route( I_\mathrmd\mathrma\mathrmp ), and arc asymmetry degree of zero aperture route( A_\mathrma\mathrmd\mathrma\mathrmp ). Then, The phenological phases of oilseed rape is identified by the decision tree (DT) algorithm based on the comparative analysis of the dynamic response of the 6 special Stokes parameters to rape growth stages.

  Results and Conclusions  Among the extracted Stokes parameters applied in this study, except \rho _m and A_\mathrma\mathrmd\mathrma\mathrmp , other parameters show great sensitivity to the change of the oilseed rape phenological phases. The DT algorithm also perform well in the classification of the oilseed rape phenological phases. The classification results agree well with the field measured samples, and the overall classification accuracy is 87.4%, while the highest classification accuracy of each phenological phase is 94.3%.