The big picture Brad Scott carrying out volcanic levelling. Did you know that scientists can tell if the ground under New Zealand bulges by just a few centimetres? Eight hundred kilometres about the city an orbiting satellite surveys Auckland with radar every three months. If the ground has started to bulge, even by a few millimetres, the system will notice the difference from the previous reading. Unlike cameras that take photographs, the radar imaging system sees through any cloud cover. Bay of Plenty image for Dec 2007 to July 2009. The colours show centimetres per year deformation rates. The blue/purple area is subsidence while the pink/red is uplift. Experts at GNS Science use a variety of techniques to monitor ground deformation including the developing field of space-based measurements. These include satellite readings, known as Interferometry, from the European Space Agency and are used to monitor the surface of our country. This technique is particularly good for monitoring vertical height changes, so is useful for volcanic terrains. Experiments to-date have been very successful in the Rotorua-Taupo area where vertical deformation signals have been recorded and compliment other sets of data such as GPS and levelling. In the future scientists hope that refinements in interferometry will allow information to be gathered and interpreted almost immediately, so that there are no delays in waiting for a diagnosis.