无人机平台的沙漠场地BRDF特征观测方法及建模

目标双向反射分布函数BRDF（Bidirectional Reflectance Distribution Function）不仅是陆面遥感的关键地球物理参数，也是星载光学遥感仪器基于地面目标的场地辐射校正重要参量，是影响定标精度的关键要素。传统野外地物多角度测量使用的观测设备，一般其结构较为复杂，重量体积较大，而且运输和组装过程繁琐，观测目标时容易受地形和交通限制，难以进行高效快速精确的野外测量。近年来，无人机由于其设备操作简便、运输和观测方式灵活等方面的优点，可作为新的观测平台应用于当前遥感试验中。本文设计了一种基于无人机平台的地表BRDF测量装置、观测方案和数据处理流程。利用多旋翼低空无人机和云台的组合，搭载野外地物光谱仪和跟拍相机，通过对地面目标多角度观测和高精度定位及角度控制，实现针对固定目标的多方位角和天顶角观测。本文采用上述设计方案和观测流程，在敦煌辐射校正场开展多次稳定均匀沙漠目标的多角度光谱观测试验，并利用实验观测数据，基于Ross-Li核驱动模型推算了场地BRDF模型参数，并与MODIS的陆表BRDF产品（MCD43C1）及反射率产品（MOD/MYD09）进行对比验证。通过开展野外实验，核验了这种新的BRDF观测手段的可靠性，获取的敦煌地表BRDF参数与MODIS遥感产品有良好的一致性，各波段的相对偏差在5%以内。本研究表明，基于多旋翼无人机的BRDF观测系统，提供了一种全新的地物目标方向反射特性观测方法，可用于自动化高频次场地特性观测以及卫星同步定标等野外实验活动。在保证观测精度的同时，极大地减轻人力物力的投入，值得广泛推广应用。

BRDF feature observation method and modeling of desert site based on UAV platform

The Bidirectional Reflectance Distribution Function (BRDF) is not only a key geophysical parameter for land surface remote sensing, but also an important parameter for radiation correction of the spaceborne optical remote sensing instruments. Observation equipment used for traditional field object multiangle measurement is generally relatively complex and heavy, and the transportation and assembly processes are cumbersome. Observing targets is easy restricted by terrain and traffic, and efficient and rapid field measurements are difficult to perform. In recent years, UAVs can be used as new observation platforms in current remote sensing experiments due to their advantages, such as simple operation of equipment, flexible transportation, and observation methods.A ground surface BRDF measurement device, observation scheme, and data processing flow based on a UAV platform are innovatively designed. Using a combination of a multirotor low-altitude drone and a gimbal, equipped with a portable ground object spectrometer and a follow-up camera, can provide high-precision positioning and angle control for multiangle observation of ground targets, thereby achieving multiazimuth and sky for fixed targets. This design scheme and observation process are adopted to carry out multiple multiangle spectral observation experiments of stable and uniform desert targets in the Dunhuang radiation correction field, and the experimental observation data are used to estimate the site BRDF model parameters based on the Ross-Li nuclear driving model, and MODIS. Land surface BRDF product (MCD43C1) and reflectivity product (MOD/MYD09) are compared and verified.Field experiments have verified the reliability of this new equipment. At the same time, the analysis results of observation data show that the BRDF parameters of Dunhuang surface measured by the proposed device have good consistency with MODIS remote sensing products, and the relative deviation of each band is within 5%.This study shows that the BRDF observation system based on multirotor drones provides a new and flexible observation method for the reflection characteristics of ground objects in the direction of the target. It can greatly reduce the investment of manpower and material resources while ensuring the accuracy of observation, which is worthy of widespread promotion and application.