A Comparative Study of the Bidirectional Reflectance Distribution Function of Several Surfaces as a Mid-Wave Infrared Diffuse Reflectance Standard

The Bi-Directional Reflectance Distribution Function (BRDF) has a well defined diffuse measurement standard in the ultraviolet, visible, and near infrared (NIR), Spectralon. It is predictable, stable, repeatable, and has low surface variation because it is a bulk scatterer. In the mid-wave IR (MWIR) and long-wave IR (LWIR), there is not such a well-defined standard. There are well-defined directional hemispherical reflectance (DHR) standards, but the process of integrating BRDF measurements into DHR for the purpose of calibration is problematic, at best. Direct BRDF measurement standards are needed. This study use current calibration techniques to ensure valid measurements and then systematically investigates the BRDF and its variation for eight potential MWIR diffuse BRDF standards. Diffuseness, repeatability, and reflectance are all considered as required parameters necessary for a diffuse MWIR BRDF standard. This document shows comparatively that Spectralon is an excellent candidate for a diffuse MWIR BRDF standard.