Detection of gas characteristics, especially the detection of the gas composition, the temperature and/or humidity of a gas, by measuring the speed of sound with a sound sender and a sound receiver both mounted on common structure. A method for determining the humidity of the scavenge air of an internal combustion engine. A speed of sound based gas sensor arrangement adapted to measure gas characteristics, especially the gas composition, the temperature and/or the humidity of a gas, including a sender, a receiver and a signal processing unit. The speed of sound is determined by driving the sender and receiver at different operation cycles in order to differentiate between the different travel times of the sound through the gas and the common structure of solid material.
