林火干扰区全极化SAR影像的散射特性分析

Analysis of fire disturbed forests scattering characteristics using polarimetric SAR image

目前,利用合成孔径雷达(synthetic aperture Radar,SAR)影像进行林火监测主要限于从林火前后时相的单极化通道振幅数据或者火后全极化影像振幅数据开展,而从林火对森林散射机制改变角度开展多时相全极化SAR林火监测的研究还较少。以2009年阿拉斯加地区发生的林火为例,以林火发生前后获取的Radarsat-2全极化影像为实验数据,从林火所改变的森林后向散射强度和散射机制角度,对林火发生前后各个极化通道后向散射强度、主导散射机制和去极化作用参数进行了定量分析,并对变化原因给出了解释。研究表明,对于北方森林,林火发生后林火干扰区的后向散射强度在同极化通道相比林火前增加了20%,交叉极化通道也有小幅增加,主导散射由林火前占59%的体散射变为林火后占53%的表面散射,去极化作用相比林火前减小45%。这些结论对于利用多时相全极化SAR数据开展林火燃烧面积或者燃烧强度监测具有参考价值。

So far forest fire monitoring is only confined to single channel polarimetric amplitude data before and after fire or the utilization of the amplitude of the fully polarimetric SAR after fire,and less research have been conducted from the viewpoint of applying change of the scattering mechanism by forest fire to monitoring forest fire by using fully polarimetric SAR. In this paper,the authors analyzed a forest fire that occurred in 2009 in Alaska,used Radarsat- 2 fully polarimetric SAR data obtained before and after the fire and,from the aspect of forest fires changing backscatter intensity and changing forest scattering mechanisms,quantitatively analyzed the intensity of each polarization channel,the dominant scattering mechanism and depolarization parameters and gave reasons for each change. The results obtained by the authors show that,for boreal forests after fire,the backscatter intensity increased by 20% in co- pol channels,and cross- pol channel increased slightly,that forest dominant scattering mechanism changed from volume scattering accounting for 59% before the fire to surface scattering accounting for53% after the fire,and that depolarization of forests was reduced by 45% in comparison with things before fire.These conclusions have reference values for applying multitemporal polarimetric SAR data to mapping forest fire scar or monitoring burn severity.