Comparison of several surfaces for use as a MWIR BRDF standard

Abstract

The Bidirectional Reflectance Distribution Function (BRDF) has a well defined and studied 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 systematically investigates the BRDF and its variation for six potential MWIR diffuse BRDF standards. The currently accepted reflectance standard in the MWIR, Infragold®, is compared against two alternative gold-electroplated arc-sprayed aluminum samples, a silver-painted arc-sprayed aluminum sample, a black-paint sample, Spectralon®, and a novel a laser beam diffuser that has been gold coated. Diffuseness is compared by fitting the data to BRDF models, and repeatability is measured by using the standard deviation and percent difference from the mean calculated from multiple BRDF measurements across the surface of the samples.