Tian Wenxin, Tang Lingli, Chen Yuwei, Li Ziyang, Zhu Jiajia, Jiang Changhui, Hu Peilun, He Wenjing, Wu Haohao, Pan Miaomiao, Lu Jing, Hyyppä Juha
Key Laboratory of Quantitative Remote Sensing Information Technology, Aerospace Information Research Institute, Chinese Academy of Sciences (CAS), Beijing 100094, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Sensors (Basel). 2021 Apr 23;21(9):2960. doi: 10.3390/s21092960.
Hyperspectral LiDAR (HSL) is a new remote sensing detection method with high spatial and spectral information detection ability. In the process of laser scanning, the laser echo intensity is affected by many factors. Therefore, it is necessary to calibrate the backscatter intensity data of HSL. Laser incidence angle is one of the important factors that affect the backscatter intensity of the target. This paper studied the radiometric calibration method of incidence angle effect for HSL. The reflectance of natural surfaces can be simulated as a combination of specular reflection and diffuse reflection. The linear combination of the Lambertian model and Beckmann model provides a comprehensive theory that can be applied to various surface conditions, from glossy to rough surfaces. Therefore, an adaptive threshold radiometric calibration method (Lambertian-Beckmann model) is proposed to solve the problem caused by the incident angle effect. The relationship between backscatter intensity and incident angle of HSL is studied by combining theory with experiments, and the model successfully quantifies the difference between diffuse and specular reflectance coefficients. Compared with the Lambertian model, the proposed model has higher calibration accuracy, and the average improvement rate to the samples in this study was 22.67%. Compared with the results before calibration with the incidence angle of less than 70°, the average improvement rate of the Lambertian-Beckmann model was 62.26%. Moreover, we also found that the green leaves have an obvious specular reflection effect near 650-720 nm, which might be related to the inner microstructure of chlorophyll. The Lambertian-Beckmann model was more helpful to the calibration of leaves in the visible wavelength range. This is a meaningful and a breakthrough exploration for HSL.
高光谱激光雷达（HSL）是一种具有高空间和光谱信息探测能力的新型遥感探测方法。在激光扫描过程中，激光回波强度受多种因素影响。因此，有必要对HSL的后向散射强度数据进行校准。激光入射角是影响目标后向散射强度的重要因素之一。本文研究了HSL入射角效应的辐射定标方法。自然表面的反射率可模拟为镜面反射和漫反射的组合。朗伯模型和贝克曼模型的线性组合提供了一种可应用于从光滑到粗糙各种表面条件的综合理论。因此，提出了一种自适应阈值辐射定标方法（朗伯 - 贝克曼模型）来解决由入射角效应引起的问题。通过理论与实验相结合的方式研究了HSL后向散射强度与入射角之间的关系，该模型成功量化了漫反射和镜面反射系数之间的差异。与朗伯模型相比，所提模型具有更高的定标精度，本研究中对样本的平均改进率为22.67%。与入射角小于70°时的校准前结果相比，朗伯 - 贝克曼模型的平均改进率为62.26%。此外，我们还发现绿叶在650 - 720 nm附近有明显的镜面反射效应，这可能与叶绿素的内部微观结构有关。朗伯 - 贝克曼模型在可见波长范围内对叶片校准更有帮助。这对HSL来说是一次有意义的突破性探索。
