AVTIS was designed to be a portable instrument so that it could be set up to look at a volcano wherever and whenever it was needed in the field. Using millimetre waves for the radar signal was ideal since the size of the antenna dish is only 30cm across and the instrument is small enough to be set up on a surveying tripod.

Portability also limited the choice of how to make the radar measurement. Many radars use a short pulse of high power as a transmit signal so that the small echo reflected from a target is loud enough to detect. Since all of the power to run AVTIS is supplied from batteries carried with the instrument, the radar can only transmit a low power beam (200mW - a little less power than a mobile phone signal) which is not very much to reflect off of natural rock. However, AVTIS can still detect radar reflections at long distances (up to 7km) because it transmits a signal continuously. This means that over time the total power beamed at the target builds up and the reflection back from the volcano is large enough to detect.

So how does the radar build up a picture of the shape of the lava dome and how can this be uses to help tell is there might be an eruption? The best way to explain the process is to look at some real data and show how each step of scanning the volcano works.