硫酸钡漫反射板在250～400nm光谱辐射亮度标定中的应用研究

Application of BaSO_4 Diffuser Plate in 250-400 nm Spectral Radiance Calibration

表面喷涂硫酸钡的漫反射板正入射时是最接近朗伯特性的用于标定光谱辐射亮度的实用漫反射板。通过实验测量硫酸钡漫反射板 2 5 0～ 4 0 0nm的半球反射率和双向反射分布函数表明 ,实测的双向反射分布函数与假定漫反射板为朗伯表面根据测量的半球反射率计算的双向反射分布函数的相对差值为 6 7% ,实测的双向反射分布函数随散射角的变化可达 2 8%。为提高光谱辐射亮度标定的准确性 ,考虑双向反射分布函数的微小变化和漫反射板上的光谱辐射照度的不均匀性 ,通过对光谱仪视场内每一小面元积分 ,最后可精确求得所测光谱辐射亮度 。

Sprayed BaSO 4 diffuser plate is the most Lambertian surface actually used in spectral radiance calibration known by now. Its hemispheric reflectance and Bi-directional Reflectance Distribution Functions(BRDF) were measured in the experiment. Its diffuse characteristics were compared with Lambertian surface. In order to calibrate spectral radiance more accurately, the small variation of diffuser's BRDF with scattered angles and the nonuniformity of spectral irradiance on diffuser surface illuminated by the standard lamp should be considered. By integrating the radiation flux reflected by the element area and that entering the entrance slit within the viewing area of spectrometer, the measured spectral radiance can be calculated. Further more, the spectral radiance of Lambertian surface whose BRDF was derived from hemispheric reflectance was compared with that from the average of the measured BRDF.