Each arm contains numerous antenna elements

Each arm of the GAS instrument contains numerous antennas. The signals received by these antennas are precisely correleated together through interferometry to build up a detailed picture, equivalent to 30km resolution at geostationary orbit. To further increase the detail deliverable by this 'sparse antenna', the Y-shaped antenna rotates. It only takes a half-rotation to compile a complete picture. The concept is similar to that used by ESA's SMOS, now in orbit, although SMOS does not rotate and uses longer-wavelength L-band instead.