Analysis of Bi-directional Reflectance Distribution Functions of Structured Rough Surfaces

Details of experimental and modeled Bi-directional Reflectance Distribution Functions (BRDFs) for rough aluminum surfaces are contained in this document. High energy lasers are of interest to the military for intersepting incoming threats. An issue with using high energy lasers in this way is that reflectance from the threat surface can irradiate objects not in the direct path of the laser and cause damage. BRDFs can be used to propagate reflected energy in any given geometrical scenario to determine irradiance on areas of interest.;A gonioreflectometer was used to collect reflectance data from 6061 aluminum alloy sanded and structured machined samples. The illuminating wavelength used in the experiment was 1.55 microns, and surface roughnesses varied from 15 to 45 microns over one square millimeter surface areas. Surface profiles used in the model were measured using a white light interferometer. The Beckmann Kirchhoff Scattering Theory was used to determine the field due to reflectance at an observation point in the model. Electromagnetic theory was used to determined radiometric units and BRDFs from the field determined by the scattering model. The Beckmann-Kirchhoff Scattering Theory did not arrive at BRDFs comparable to the experimental model. A geometrical ray tracing model was developed and the results convolved with the Beckmann-Kirchhoff Scattering Theory BRDFs to give comparable BRDFs.