A three-dimensional radar backscatter model of forest canopies
A three-dimensional radar backscatter model of forest canopies
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DOI：
10.1109/36.377937
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发表时间：
1995-03
影响因子：
8.2
通讯作者：
G. Sun;K. Ranson
中科院分区：
文献类型：
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作者：
G. Sun;K. Ranson
描述了一种充分考虑林木在林分中空间位置的三维森林后向散射模型。将林分按任意空间分辨率划分为单元。这些细胞可能包括“树冠”、“树干”和“树隙”成分，由树木的形状、大小和位置决定。森林地面由一层“地面”细胞表示。用射线追踪法计算了1)树冠直接后向散射、2)地面直接后向散射、3)树干直接后向散射、4)树冠-地面散射和5)树干-地面散射的后向散射分量。此外，还利用光线追踪法计算了微波信号在非“带隙”单元内的衰减和时延。这些分量在相同距离间隔内的后向散射Mueller矩阵被非相干地相加，以得到图像像素的总后向散射。通过假设图像斑点噪声为零均值乘性高斯噪声，将高分辨率图像聚合成具有给定空间分辨率和独立样本数的合成孔径雷达图像。用美国缅因州150m×200m的典型林分对模型进行了参数化处理。将模拟的雷达后向散射系数与实际的喷气推进合成孔径雷达数据进行了比较。该模型合理地预测了整个测站的平均后向散射系数，所有通道的模型与数据的一致性均在1.35分贝以内。在所有频率(P、L和C波段)和极化(HH、HV和VV)下，模拟图像和合成孔径雷达数据(10x15像素)之间的相关性在0.001水平上都是正的且显著的。
three-dimensional forest backscatter model, which takes full account of spatial position of trees in a forest stand is described. A forest stand was divided into cells according to arbitrary spatial resolution. The cells may include "crown," "trunk," and "gap" components, determined by the shape, size and position of the trees. The forest floor is represented by a layer of "ground" cells. A ray tracing method was used to calculate backscattering components of 1) direct crown backscatter, 2) direct backscattering from ground, 3) direct backscattering from trunk, 4) crown-ground scattering, and 5) trunk-ground scattering. Both the attenuation and time-delay of microwave signals within cells other than "gap" were also calculated from ray tracing. The backscattering Mueller matrices of these components within the same range intervals were incoherently added to yield the total backscattering of an image pixel. By assuming a zero-mean, multiplicative Gaussian noise for image speckle, the high-resolution images were aggregated to simulate a SAR image with a given spatial resolution and number of independent samples (looks). A well-characterized 150 m x 200 m forest stand in Maine, USA, was used to parameterize the model. The simulated radar backscatter coefficients were compared with actual JPL SAR data. The model gives reasonable prediction of backscattering coefficients averaged over the entire stand with agreement between model and data within 1.35 dB for all channels. The correlations between simulated images and SAR data (10 by 15 pixels) were positive and significant at the 0.001 level for all frequencies (P, L, and C bands) and polarizations (HH, HV, and VV).