The present invention provides a system for use in a vehicle for determining an indication of the type of terrain in the vicinity of the vehicle. The system comprises a processor arranged to receive acoustic sensor output data from at least one vehicle-mounted acoustic sensor, the or each acoustic sensor being arranged to receive a reflected signal from the terrain in the vicinity of the vehicle, the processor also being arranged to calculate at least one acoustic parameter in dependence on the acoustic sensor output data. The system also comprises a data memory arranged to store pre-determined data relating the at least one acoustic parameter to a particular terrain type. The processor is arranged to compare the at least one acoustic parameter with the pre-determined data to determine an indication of the particular terrain type based on the acoustic sensor output data only.