A methodology for measuring the effectiveness of spray suppression devices on heavy trucks is discussed. An instrumentation system concept is described which would permit field measurements of the apparent contrast of an object, viewed through a spray cloud, separate from the confounding influence of veiling luminance due to uncontrolled ambient lighting conditions. Both transmissivity and scattered light measurements are considered; advantages and disadvantages of each and problems in their application are discussed. An expanded beam laser transmissometer is described which has potential advantages over the simple narrow-beam laser transmissometer commonly used to measure truck spray density. Provided here are results of laboratory experiments conducted to define hardware requirements for the expanded beam laser transmissometer scheme and for instrumentation to make scattered light measurements, using a modulated laser beam to illuminate the spray cloud.
Abstract