A distance measurement apparatus arranged to measure the distance to an object (106) comprising a first sonic transmitter (100) arranged at a first distance (h1) from that object and a second sonic transmitter (102) arranged at a second distance (h2) from that object (100), wherein the first and second distances are different, the first (100) and second (102) transmitters being controlled by processing circuitry (108) and the first and second transmitters being arranged such that sonic pulses emitted, in use, thereby are incident upon that object (106) and the apparatus further comprising at least one sonic receiver (100) arranged to receive a plurality of reflected sonic pulses and generate an output therefrom and the processing circuitry (108) being arranged to receive the output, determine the times since the first and second pulses were emitted and generate a distance to that object from the determined times.