Abstract: A plant matter sensor, the sensor includes a pair of parallel spaced apart sensor arms and a control console, a first of the arms having a plurality of emitter means spaced along its length, each emitter configured and arranged to, in use, emit a signal substantially perpendicularly to the arm to be received by a corresponding receiver on the second arm. The console contains controller means to, in use, control the rate, strength and regularity of the signal emitted by each of the said emitters, collectors to, in use, collect data from each receiver as to the existence or absence of receipt of a signal, a processor to process data received from the controllers and the collectors and determine the height of any plant matter traversed by the plant matter sensor and predetermined intervals, and storage to store the plant matter height data generated by the processor for subsequent download or analysis.