为了实现室外BRDF的准确测量,设计了多角度测量系统。测量系统包括一台自动测量架和两台ASD(Analytical Spectral Devices)公司生产的野外型光谱仪,光谱仪的光谱分辨率为3nm,一台光谱仪固定在测量架平台上测量目标各方向反射,另一台光谱仪放置在地面上同时测量漫反射板反射。应用该系统进行了室外草地的测量实验,测量整个周期(66个方向点)用时10min,测量主平面(间隔5°,共31个方向点)用时2.5min。测量结果显示目标的反射为非朗伯性,并在主平面的反射方向性最强烈。

In order to acquire field Bidirectional Reflectance Distribution Function (BRDF) of targets,a multiangular measurement system was designed.The system includes an automated goniometer and two ASD FieldSpec spectroradiometers with spectral resolution of 3nm.One ASD spectroradiometer was placed on the platform of goniometer measured reflectance of target,meanwhile,the other placed on the ground acquired reflectance of reference panel.We measured the BRDF of meadow by use of this system.A hemispherical measurement (66 positions) was done in about 10 minutes and the principal plane measurement (interval 5°,31 positions) was carried out in about 2.5 minutes.The measurement results show the non-Lambertian characters of the target,which exposes obvious directional reflectance in principal plane with strong back-scattering and a less developed forward scattering.