The presence of dirt in the cane supply is a major cost to Australia's raw sugar industry. Automatic control of the base cutter height of chopper harvesters might be an effective way to reduce the amount of dirt in the cane supply. Fluctuation of the pressure drop across the hydraulic motor driving a base cutter disk was not found to be a good indicator cutting height. Preliminary trials with automatic systems of base cutter height control based on ultrasonic range finding principles were also performed. Such systems seemed to offer some promise in burnt cane, but there was interference from spurious echoes when harvesting cane.