Product Code: ILSC2007_1406

Empirical BRDF Modeling of a Window to Improve Accuracy of Laser Reflection Hazard Analyses
Authors:
George Megaloudis, Northrop Grumman Corporation; Andover MA USA
Kenneth Keppler, Northrop Grumman Corporation; San Antonio TX USA
Edward Early, Northrop Grumman Corporation; San Antonio TX USA
Paul Kennedy, AFRL/HEDO; Brooks City-Base TX USA
Presented at ILSC 2007

Laser reflections from window surfaces have traditionally been treated as specular (i.e., the energy or power of the beam is reduced but the divergence of the beam remains unchanged). An empirical Bi-directional Reflectance Distribution Function (BRDF) model was developed for a spare aircraft window, based on measurements and Maxwell-Beard theory. This empirical model was then used in a reflection hazard analysis tool to calculate hazard distances for laser reflections from the window surface. The measurements and model demonstrate that the window increases the divergence of the reflected beam by a factor of approximately 100 over the divergence of the incident beam. This increase in the divergence decreases the traditionally calculated hazard distance by the same factor. Therefore, more accurate, and shorter, hazard distances due to laser reflections from windows will be obtained if the BRDF of the windows are measured and modeled rather than assumed to be ideal.