A system for use in a vehicle for determining an indication of the type of terrain in the vicinity of the vehicle, the system comprising: a processor arranged to receive acoustic sensor output data from at least one vehicle-mounted acoustic sensor, the or each acoustic sensor including an acoustic transmitter and acoustic receiver and being arranged to receive a reflected signal from an insonified section of the terrain in the vicinity of the vehicle, and a data memory arranged to store pre-determined data relating at least one acoustic parameter to a particular terrain type; characterized in that the processor is arranged to: divide the received acoustic sensor output data from the or each sensor into at least two data sets, each data set corresponding to acoustic signals reflected from a different swathe of the insonified section of the terrain, wherein the insonified section is divided into at least two swathes in a longitudinal direction ahead of the vehicle and, for each swathe, the output data comprises a plurality of discrete data points, calculate at least one acoustic parameter in dependence on the received acoustic sensor output data for each swathe, and compare the acoustic parameters with the pre-determined data to determine an indication of the particular terrain type based on the acoustic sensor output data only. a processor arranged to receive acoustic sensor output data from at least one vehicle-mounted acoustic sensor, the or each acoustic sensor including an acoustic transmitter and acoustic receiver and being arranged to receive a reflected signal from an insonified section of the terrain in the vicinity of the vehicle, and a data memory arranged to store pre-determined data relating at least one acoustic parameter to a particular terrain type; characterized in that the processor is arranged to: divide the received acoustic sensor output data from the or each sensor into at least two data sets, each data set corresponding to acoustic signals reflected from a different swathe of the insonified section of the terrain, wherein the insonified section is divided into at least two swathes in a longitudinal direction ahead of the vehicle and, for each swathe, the output data comprises a plurality of discrete data points, calculate at least one acoustic parameter in dependence on the received acoustic sensor output data for each swathe, and compare the acoustic parameters with the pre-determined data to determine an indication of the particular terrain type based on the acoustic sensor output data only. divide the received acoustic sensor output data from the or each sensor into at least two data sets, each data set corresponding to acoustic signals reflected from a different swathe of the insonified section of the terrain, wherein the insonified section is divided into at least two swathes in a longitudinal direction ahead of the vehicle and, for each swathe, the output data comprises a plurality of discrete data points, calculate at least one acoustic parameter in dependence on the received acoustic sensor output data for each swathe, and compare the acoustic parameters with the pre-determined data to determine an indication of the particular terrain type based on the acoustic sensor output data only.