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DOI:

10.11834/jrs.20210144

收稿日期:

2020-05-19

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PolInSAR森林高度反演中方法及波段选择引起的不确定性分析
张庭苇1,2,姬永杰3,张王菲1
1.西南林业大学 林学院, 昆明 650224;2.长沙市规划信息服务中心, 长沙 410004;3.西南林业大学 地理与生态旅游学院, 昆明 650224
摘要:

森林高度是反映森林资源数量和质量的重要参数,极化干涉合成孔径雷达PolInSAR (Polarimetric Synthetic Aperture Radar Interferometry)技术在森林高度反演中极具潜力。由于森林散射特征受波长影响明显,由此引起的散射机理差异使得基于PolInSAR技术反演的森林高度结果具有很大的不确定性。为了定量化该不确定性的影响,本文以模拟森林场景为例,对PolInSAR技术森林高度反演中常用的4种方法——极化相位中心高度估测法、复相干相位中心差分法、复相干幅度反演法以及相干幅度、相位联合反演法,以及它们在常用的4个微波波段P、L、C和X中的森林高度估测结果进行了分析;明确了匀质森林场景中,算法、波段选择引起的森林高度估测结果的不确定性。研究结果表明:在森林场景基本一致的情况下,估测算法的选择直接影响森林高度估测结果,其中复相干幅度反演法在4个波段的估测结果中精度均最高,但各估测点的估测结果离散度及不确定度较大。波长对4类估测方法估测结果的影响差异明显:复相干幅度反演法的反演结果几乎不受波长的影响,而相干幅度、相位联合反演法受波长影响明显,在P和L波段反演结果中精度较高,在C和X波段反演结果中精度降低明显。此外,以传统的交叉极化(HV)相位代表冠层散射相位中心,水平同极化与垂直同极化的相位差(HH-VV)代表地表散射相位中心,采用复相干相位中心差分法进行森林高度估测会出现严重低估现象。估测结果不确定度具有波长和算法选择依赖性,在C和X波段采用复相干相位中心差分法估测结果不确定度最低,在P和L波段采用极化相位中心高度估测法估测结果不确定度最低,而复相干幅度反演法估测结果则在多个波段中的不确定度均最高。

The analysis on uncertainty resulting from method and wavelength selecting in forest height inversion using simulated polarimetric interferometric SAR data
Abstract:

Forest height is an important indicator for representing the quality and quantity of forest resources. Polarimetric synthetic aperture radar interferometry (PolInSAR) technology has been demonstrated and validated as a potential way for forest height inversion and mapping in recent years. Airborne and spaceborne PolInSAR data have been applied in a variety of temperate, boreal, and tropical forests. However, for the distinctions of forest scattering mechanisms at different microwave length and the different theory-base of each estimation algorithm, uncertainties usually occurred during the procedure of forest height estimation and mapping using PolInSAR data. In order to clarify the uncertainties resulting from the selection of different microwave wavelength algorithms in the procedure of forest height inversion, this study discussed the effects caused by the four selected inversion algorithms and four typical microwave wavelength using a simulated forest scene. The four inversion algorithms include polarimetric phase center height estimation method (PPC), complex coherence phase center differencing algorithm (CCPCD), coherence amplitude inversion method (CAI), and hybrid inversion method using both phase and coherence information. The involved microwave bands are at P, L, C, and X bands. Results of this study demonstrated that the effects of the wavelength and estimation algorithm are evident on the performance of forest height estimation using PolInSAR data. First, the selected estimation algorithm directly affects the results accuracy of forest height estimation when the microwave wavelength is the same. The estimated results from CAI agree well with the average forest height in the simulated forest scene and show best performance at the four selected microwave bands, but the degrees of dispersion and the ratios of uncertainty of the estimated results are also highest among the four inversion algorithms. Second, it shows obvious effects of microwave wavelength on the performance of the four selected inversion algorithms. It shows no obvious effect on CAI method. However, it shows great effects on the performance of the hybrid inversion method. The estimation results acquired from hybrid inversion method show a better performance at long wavelength (P- and L- bands), but a worse performance at short wave length (C- and X- bands). Moreover, the results reveal great underestimation of CCPCD method, which usually using HV channel phase as the canopy scattering phase center and the phase difference between HH and VV channels as the surface scattering phase center to retrieve the forest height. T The uncertainties of estimation results depend on wavelength and algorithm selections. Short wavelength with CCPCD method and long wavelength with PPC method show better performance and the lowest uncertainties on forest height estimation, whereas CAI method shows the highest uncertainties in forest height estimation at P, L, C, and X bands.

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