The MetOp satellites each weighs over 4000 kg and measure 17.6 m x 6.5 m x 5.2 m after the solar array and antennas have deployed following launch. The animation shows how the Advanced Scatterometer (ASCAT) and the Global navigation satellite system Receiver for Atmospheric Sounding (GRAS) open. ASCAT measures wind over the oceans. ASCAT transmits pulses of microwave energy towards the surface of Earth and records the resulting echoes to derive wind speed and direction over the ocean. Since observations are made using radar, ASCAT provides day and night imaging and is not affected by clouds. GRAS uses radio occultation to measure vertical profiles of atmospheric temperature and humidity by tracking signals received from a constellation of navigation satellites while they are rising or setting behind Earth’s atmosphere.