SMOS mission overview   From an altitude of 763 km, the SMOS antenna will view an area almost 3000 km in diameter. Because of the Y-shaped antenna and the interferometry measurement principle, the field-of-view is limited to a hexagon-like shape about 1000 km across.   Interferometry measures the phase difference between electromagnetic waves at two or more receivers, which are a known distance apart (baseline). As long as the observed phase difference can be related to waves emitted at the same time, the origin of the wave can be determined. Last update: 2 November 2009