As part of an existing NERC project we have designed and built a new type of ground-based remote sensing instrument: a combined millimetre-wave radar and radiometer called the All-weather Volcano Topography Imaging Sensor (AVTIS). We are testing the ability of this instrument to measure the changing shape of lava flows under all conditions, through cloud and at night. Etna is one of the test sites and we would like to obtain lidar data of the lava flow surfaces to validate the ground-based AVTIS measurements.