A spinning radar that measures wind speed and direction over the ocean. ISRO has flown it on Oceansat-2, ScatSat-1 and EOS-06.
Wind makes small ripples on the sea. A scatterometer sends radar pulses down and measures how strongly the ripples echo them back. Stronger winds make rougher water and stronger echoes. By looking at the same patch from several angles, the instrument works out both wind speed and direction, day or night, through cloud.
ISRO's Space Applications Centre in Ahmedabad designed it. On Oceansat-2 a 1 m dish spun at 20.5 turns a minute, sweeping two radar beams in circles over a strip about 1,400 km wide. Winds are reported on grids of 25 km and 50 km.
The first scatterometer, OSCAT, flew on Oceansat-2 from 2009. Weather agencies in the US and Europe also used its winds. It failed in February 2014 when a transmitter part broke, shortly before its planned five-year life.
ScatSat-1, launched by PSLV-C35 in September 2016, carried a similar instrument to fill the gap, for weather forecasts and cyclone tracking. EOS-06 (Oceansat-3), launched in November 2022, carries the next version, SCAT-3.