The six-band weather camera on INSAT-3D, INSAT-3DR and INSAT-3DS. It images the Earth disc in visible and infrared light, including at night, every half hour or less.
The imager has six channels. A visible and a short-wave infrared channel see clouds, snow and land at 1 km detail. A mid-wave infrared channel at 4 km picks out low cloud and fog at night and helps find forest fires. A water vapour channel at 8 km shows moisture high in the air. Two thermal infrared channels at 4 km measure the temperature of cloud tops and the sea surface.
It is an improved version of the VHRR flown on Kalpana-1 and INSAT-3A, with six channels instead of three. A scan mirror sweeps the telescope across the Earth line by line. The spacecraft corrects the mirror's pointing in real time for small wobbles caused by the sounder's own mirror.
INSAT-3D (2013), INSAT-3DR (2016) and INSAT-3DS (2024) carry the imager. INSAT-3D and INSAT-3DR have been run in step so that, between them, a new image arrives every 15 minutes. The India Meteorological Department processes the data into products such as cloud motion winds, rainfall estimates, sea surface temperature, fog and snow cover.