摘要: 目的水云模型（WCM）是一种采用SAR数据反演森林地上生物量（AGB）应用较为广泛的半经验模型，探索将不同波长、极化方式、极化信息等引入WCM，以期为提高森林AGB反演精度提供科学依据、�/sec> 方法本文以X、C、L、P波段多频极化SAR数据为数据源，首先将各波长各极化后向散射系数用于WCM进行森林AGB反演，对比其反演精度；接着采用极化分解分量构建地体散射比参数，并将其引入WCM发展为极化水云模型（PolWCM），同时对比分析其在X、C、L、P波段森林AGB的反演结果、�/sec> 结果�?）在X、C、L、P 4个波段中，除X波段外，将HV极化后向散射系数代入WCM进行森林AGB反演，精度均高于基于其他极化通道后向散射系数的反演结果；且长波长（L和P）的反演精度高于短波长（X和C）的反演精度。在L波段，将HV极化后向散射系数代入WCM进行森林AGB反演＋�i>R ²和RMSE分别�?.46�?8.00 t/hm ²；P波段HV极化反演结果皃�i>R ²和RMSE分别�?.43�?1.18 t/hm ²。（2）将极化信息以地体散射比的形式引入WCM，PolWCM模型在X、C、L、P各个波段均可提高反演精度，反演结果的RMSE值分别为24.90�?4.71�?7.70�?8.08 t/hm ²、�/sec> 结论采用WCM进行森林AGB反演具有极化、波长依赖性，其中将L波段HV极化后向散射系数代入WCM进行森林AGB反演时精度最优；将极化信息以地体散射比的方式引入WCM，发展PolWCM，可以明显提高森林AGB的反演精度、�/sec>

关键诌�
• X、C、L、P 波段SAR数据/
• 森林地上生物野�/a> /
• 极化/
• 地体散射毓�/a>

Abstract: ObjectiveWater cloud model (WCM) is a semi empirical model using SAR data to retrieve forest aboveground biomass (AGB). The objective of this study is to explore the capability of introducing different wavelengths at different polarization channels into WCM for forest AGB inversion. And through the exploration, it is expected to provide scientific reference for improving the accuracy of forest AGB retrieval. MethodIn this paper, firstly, we applied WCM in forest AGB estimation at X-, C-, L- and P-band with HH, HV, and VV polarizations, respectively, and their results were compared and analyzed. Then a parameter named the ratio of surface scattering power and volume scattering power was constructed based on polarization decomposition components and embedded in WCM, here we named it PolWCM. The potential of PolWCM on forest AGB estimation was explored by X-, C-, L- and P-band polarimetric decomposition components. Result(1) HV backscattering coefficients showed best performance in forest AGB estimation using WCM at C-, L- and P-band, among them, L- and P-band performed better than X- and C-band ( R ²= 0.46, RMSE = 18.0 t/ha for L-band and R ²= 0.43, RMSE = 21.18 t/ha for P-band). (2) PolWCM performed better than WCM for forest AGB estimation at X-, C-, L- and P-band, respectively. Their RMSE values for X-, C-, L- and P-band were 24.90, 24.71, 17.70 and 18.08 t/ha, respectively. ConclusionThe forest AGB estimation of WCM shows obvious dependence on wavelength and polarization, HV backscatter coefficients at L-band perform best in forest AGB estimation. Polarimetric information embedded in WCM through the ratio of surface scattering power and volume scattering power can improve the forest AGB estimation accuracy.

Key words:
• SAR data of X-, C-, L- and P-band/
• forest aboveground biomass/
• polarization/
• ratio of surface scattering power and volume scattering power

�?nbsp; 1研究区地理位�?/p>

Figure 1.Geographic location of the study area

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�?nbsp; 2X、C、L、P 4个波段覆盖范围概况图及地理编码后Pauli RGB

HH和HV分别为HH和HV两个极化后向散射系数。HH and HV are polarization backscattering coefficients of HH and HV, respectively.

Figure 2.Overview of the coverage of SAR data and their geocoded images displayed as Pauli RGB at X-, C-, L- and P-band

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�?nbsp; 3多频SAR数据预处理技术路纾�/p>

“――”代表数据提供方已作辐射定标，本文不需再作定标。“――� means that the data provider has made radiometric calibration and no further calibration is required in this paper.

Figure 3.Flowchart of multifrequency SAR data preprocessing technology

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�?nbsp; 4LiDAR提取研究区相关数�?/p>

Figure 4.LiDAR extracts relevant data of the study area

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�?nbsp; 5X、C、L、P波段WCM反演森林AGB

散点图中的红色实体线为森林AGB估测值拟合线，黑色点为训练样本，蓝色点为验证样本。图中RMSE单位为t/hm²。下同。The red solid line in the scatter diagram is the fitting line of forest AGB estimation values, the black points are the training samples, and the blue points are the verification samples. The unit of RMSE is t/ha. The same below.

Figure 5.X-, C-, L-, P-band WCM inversion results of forest AGB

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�?nbsp; 6X、C、L、P波段PolWCM反演森林AGB结果

F_Odd咋�i>F_Vol分别为Freeman极化分解三分量中的地表散射与体散射分量、�i>F_OddandF_Volare the surface scattering and volume scattering components of Freeman polarization decomposition.

Figure 6.Forest AGB retrieved by PolWCM at X-, C-, L- and P-band

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�?nbsp; 1根河试验区X、C、L、P波段数据详细参数

Table 1.X -, C -, L -, P-band data parameters in Genhe Experimental Area

荷载及星�?br/>Load and constellation	所属国宵�br/>Nation	获取时间 Acquisition time	中心入射觑�br/>Central incidence angle/（°）	距离向分辨率 Range resolution/m	方位向分辨率 Azimuth resolution/m
TerraSAR-X X-band	德国 Germany	2015�?8�?9	41.41	0.91	2.68
RADARSAT-2 C-band	加拿�?br/>Canada	2013�?8�?0	46.09	4.96	4.73
ALOS-2 PALSAR-2 L-Band	日本 Japan	2014�?8�?9	36.52	2.86	2.64
Airborne CAMSAR P-Band	中国 China	2013�?9�?3	50.06	0.63	0.67

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�?nbsp; 2X、C、L、P波段WCM反演结果

Table 2.Inversion results of WCM for X-, C-, L- and P-band

波段 Band	极化通道 Polarization channel	R2	RMSE/(t·hm�?) RMSE/(t·ha�?)
X	HH	0.03	26.12
	HV	0.01	26.49
	VV	0.05	25.70
C	HH	0.19	24.32
	HV	0.33	23.32
	VV	0.30	22.76
L	HH	0.24	21.27
	HV	0.46	18.00
	VV	0.30	20.34
P	HH	0.12	27.40
	HV	0.43	21.18
	VV	0.09	27.04

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�?nbsp; 3X、C、L、P 波段PolWCM反演森林AGB结果

Table 3.Inversion forest AGB results of PolWCM for X-, C-, L- and P-band

参数 Parameter	波段 Band	R2	RMSE/(t·hm�?) RMSE/(t·ha-1)
FOdd/FVol	X	0.00	24.90
	C	0.01	24.71
	L	0.40	17.70
	P	0.51	18.08
注：FOdd咋�i>FVol分别为Freeman极化分解三分量中的地表散射与体散射分量。Note:FOddandFVolare the surface scattering and volume scattering components of Freeman polarization decomposition.

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