Stokes参数在油菜长势监测中的可行性分析

Feasibility Analysis of Stokes Related Parameters for Oilseed Rape Growth Monitoring

合成孔径雷达(synthetic aperture radar,SAR)对地观测可以获得地物的散射信息,正确有效的SAR信息解译是采用SAR技术进行遥感监测的基础。首先以假设的水平发射、垂直和水平接收的电磁波为基础,构建并计算了研究区覆盖油菜整个生长周期的Stokes参数及其子参数;然后分别分析了这些参数与油菜地上生物量(above ground biomass,AGB)、高度和叶面积指数(leaf area index,LAI)等长势参数的相关性及重要性,创新性地将Stokes参数引入农作物长势监测中,探索了Stokes相关参数在油菜长势参数反演中的可行性。研究结果表明:表征能量的Stokes参数,如总能量g0等与油菜AGB相关性较高,在AGB反演的输入参数重要性分析中,其重要性也大于其他参数;表征地物散射特征的Stokes参数,如极化度m、线极化度ml和线极化比μl等与高度和LAI的相关性较高,这些参数在反演中的重要性也较高。因此在农作物高度和LAI的反演中,可优先考虑表征散射极化特征的Stokes参数。同时,研究结果也表明了农作物结构特征对其散射能量的影响。

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(ml)and the ratio of linear polarization(μl)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.