Measurement and characterization of the pressure-sinkage data for snow obtained using a Rammsonde

To examine the feasibility of using the pressure-sinkage data obtained with a Rammsonde as input to a proposed module for the NATO Reference Mobility Model for predicting tracked vehicle performance over snow, a series of measurements of penetration resistance of undisturbed and preconditioned snow was made using a Rammsonde, and compared with those obtained with a bevameter and Rammsonde cones driven by a bevameter. This paper describes the results of the field measurements made using the three types of device, as well as the approaches to the characterization of the pressure-sinkage data obtained. It is found that the data obtained using the Rammsonde, the bevameter and the Rammsonde cone driven by a bevameter are, in general, comparable, considering the possible variations of terrain conditions in the field. It is shown that the pressure-sinkage equations proposed by Bekker could form a common basis for characterizing the data obtained using the three different techniques. It is found that in soft, undisturbed snow (with density less than 0.2 g/cm3), the small (or standard) Rammsonde cone of 4 cm in diameter cannot be used to obtain meaningful pressure-sinkage data within a certain snow depth. Under these circumstances, the use of the large Rammsonde cone of 10 cm in diameter is recommended. Over preconditioned snow, both the small and large Rammsonde cones could provide comparable data. The size effect of the sensing element (such as the diameter of the Rammsonde cone or the bevameter sinkage plate) on the pressure-sinkage relationships was examined. It is found that in many cases, the values of the pressure-sinkage parameters derived from data obtained using a single sensing element of 10 cm in diameter are comparable to those obtained using two sizes of sensing elements of 4 and 10 cm in diameter.