This paper analyzes the backscatter of the microwave signal in a boreal forest environment based on a Ku -band airborne Frequency-Modulated Continuous Waveform (FMCW) profiling radar—Tomoradar. We selected a half-managed boreal forest in the southern part of Finland for a field test. By decomposing the waveform collected by the Tomoradar, the vertical canopy structure was achieved. Based on the amplitude of the waveform, the Backscattered Energy Ratio of Canopy-to-Total (BERCT) was calculated. Meanwhile, the canopy fraction was derived from the corresponding point cloud recorded by a Velodyne VLP-16 LiDAR mounted on the same platform. Lidar-derived canopy fraction was obtained by counting the number of the first/ the strongest returns versus the total amount of returns. Qualitative and quantitative analysis of radar-derived BERCT on lidar-derived canopy fraction and canopy height are investigated. A fitted model is derived to describe the Ku-band microwave backscatter in the boreal forest to numerically analyze the proportion contributed by four factors: lidar-derived canopy fraction, radar-derived canopy height, the radar-derived distance between trees and radar sensor and other factors, from co-polarization Tomoradar measurements. The Root Mean Squared Error (RMSE) of the proposed model was 0.0958, and the coefficient of determination R2 was 0.912. The fitted model reveals that the correlation coefficient between radar-derived BERCT and lidar-derived canopy fraction is 0.84, which illustrates that lidar surface reflection explains the majority of the profiling /waveform radar response. Thus, vertical canopy structure derived from lidar can be used for the benefit of radar analysis.

本文基于Ku波段机载调频连续波形（FMCW）廓线雷达—Tomoradar，分析了北方森林环境中微波信号的反向散射。我们选择了芬兰南部半管理的北方森林进行田间试验。通过分解Tomoradar收集的波形，可以实现垂直顶篷结构。基于波形的幅度，计算了树冠与总背向散射的能量比（BERCT）。同时，冠层分数来自安装在同一平台上的Velodyne VLP-16 LiDAR记录的对应点云。通过计算第一个/最强回报率的数量与总回报率的比值，得出源自激光雷达的冠层分数。研究了雷达衍生的BERCT对激光雷达衍生的冠层分数和冠层高度的定性和定量分析。推导了拟合模型来描述北方森林中Ku波段微波的反向散射，以数字方式分析由以下四个因素贡献的比例：激光雷达得出的冠层比例，雷达得出的冠层高度，雷达得出的树木与雷达传感器之间的距离以及其他因素，来自同极化Tomoradar测量。该模型的均方根误差（RMSE）为0.0958，确定系数R2为0.912。拟合模型表明，雷达衍生的BERCT与激光雷达衍生的冠层分数之间的相关系数为0.84，这说明激光雷达表面反射解释了大多数轮廓/波形雷达响应。从而，