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 (1) and a sound receiver (2) both mounted on common structure (3). The invention further concerns a method for determining the humidity of the scavenge air of an internal combustion engine. The invention further concerns 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, comprising a sender (1), a receiver (2) and a signal processing unit. The speed of sound is determined by driving the sender (1) and receiver (2) at different operation cycles in order to differentiate between the different travel times of the sound through the gas and the common structure (3) of solid material.
