Photography-based real-time long-wave infrared scattering estimation technique

The scattered light distribution of surfaces in the long-wave infrared (λ∼8-12 μm) is measured using a small set of thermal camera images. This method can extract scatter patterns considerably faster than standard laboratory bidirectional reflectance distribution function measurements and is appropriate for passive homogeneous surfaces. Specifically, six images are used in this study, each taken with respect to a thermal light source at an angle ranging from 10_ to 60_ to the normal of the surface. This data is deconvolved with the shape of the light source to estimate the scattering pattern. Both highly specular (black Masonite) and diffuse (painted drywall) surfaces are tested. Errors between the estimated scattering distribution and a directly measured one using a goniometer stage and quantum-cascade laser (QCL) are less than or equal to3%except for extremely specular surfaces where viableQCL measurements cannot be made due to the increased relative contribution of speckle noise.