Surface contamination or soiling of the exterior of road vehicles can be unsightly, reduce visibility and customer satisfaction and with the increasing application of surface mounted sensors can degrade the performance of advanced driver assistance systems. Experimental methods of evaluating the surface contamination are increasingly used in the product development process but the results are generally subjective. The use of computational methods of predicting soiling make objective measures possible, but comparable data from experiment is an important validation requirement. This paper describes the development of an objective measure of base surface contamination arising during experiments. A variety of rear slant geometries of a 25% scale generic SUV model are compared through a series of controlled experiments in the Loughborough University Large Wind Tunnel. Base soiling is generated using UV doped water introduced from a known location to simulate spray from a tyre. An image of the base, illuminated by an Ultra-Violet lamp, is captured after each test along with a calibration vessel with known fluid depth. The image is processed to remove the influence of variation in incident illumination. The total mass of contamination deposited is then calculated using the calibration vessel to provide the required local fluid depths. The paper includes validation of the technique.