Feasibility Analysis of Stokes Related Parameters for Oilseed Rape Growth Monitoring

Synthetic aperture radar (SAR) has been proved as an effective tool for agricultural monitoring and its effectiveness depends on the accurate and appropriate interpretation of SAR Information. Stokes parameters, which is proposed on the dichotomy principle of electromagnetic wave, describe the changes of the incident electromagnetic wave affected by objects which are radiated by electromagnetic wave, and then obtain the information from the objects. However, to our best knowledge, few reports focus on crop phenology monitoring using Stokes parameters. This study aims to explore the feasibility of Stokes related parameters for crop growth monitoring. In this paper, Stokes parameters and their subparameters are calculated based on assumption of wave transmitted in horizontal and received in both horizontal and vertical polarization. Then these Stokes parameters are derived from 5 multi-temporal Radarsat-2 images and averaged relying on each oilseed rape field area. The correlation between all of the Stokes parameters and oilseed rape growth parameters including above ground biomass (AGB), height and leaf area index (LAI) are computed by Pearson product moment correlation coefficient. The significance of these Stokes parameters for oilseed rape AGB, height and LAI inversion are derived from random forest (RF) model. The results indicate the potential of Stokes parameter for crop growth monitoring and growth parameters inversion. It demonstrates that scattering power related Stokes parameters reveal better performance for crop AGB inversion, but scattering mechanism related Stokes parameters such as degree of polarization (m), the degree of linear polarization (m_l) and the ratio of linear polarization (μ_l) are more sensitive to crop height and LAI. Moreover, the results suggest that it is necessary to analyze the influence of crop structure on scattering power when crop growth parameters inversion is performed with Stokes parameters.