A photogrammetric method for measuring transient frost surface roughness.

Cold-soaked fuel frost (CSFF) is a form of aircraft wing contamination that results in aerodynamic degradation. Unless a certification exemption for a specific aircraft model is provided by the FAA, an operator of an aircraft is not allowed to takeoff with CSFF on aircraft wing surfaces. To assist manufacturers in the design of air vehicles and to assist the FAA in evaluating exemption requests, frost roughness evolution must be characterized and modeled. However measuring transient frost roughness is difficult because of the optical and material properties of frost. This experimental investigation presents a nonintrusive, in-situ method of measuring frost roughness using structure-from-motion photogrammetry. This method was validated with fabricated rough surfaces and was used on a closed-loop psychrometric wind tunnel that is capable of producing frost formations in various environmental conditions. The resulting roughness parameters and detailed height distributions were analyzed to determine the effects of each environmental variable.