The weather camera that watched India's skies from geostationary orbit for three decades, on the INSAT-1 and INSAT-2 satellites, Kalpana-1 and INSAT-3A.
VHRR takes pictures of the whole Earth disc as seen from geostationary orbit. In visible light it sees clouds by day. In thermal infrared it measures how warm cloud tops and the ground are, day and night. Cold, high cloud tops mark storms.
On the INSAT-2 satellites it had 2 km resolution in visible light and 8 km in infrared. INSAT-2E added a third band for water vapour, a first for INSAT. Kalpana-1 and INSAT-3A carried the three-band version.
VHRR is a whiskbroom imager. A scan mirror sweeps the view of a small telescope, about 20 cm across, across the Earth line by line. ISRO designed and built it as an improvement on the VHRR of the INSAT-1 series, whose resolution was 2.75 km in visible and 11 km in infrared.
VHRR gave forecasters regular cloud pictures, and winds worked out by tracking how clouds and water vapour features move. It flew on INSAT-2A, 2B, 2D and 2E in the 1990s, then on Kalpana-1 (2002) and INSAT-3A (2003). Kalpana-1's VHRR sent a full-disc image every half hour. Its successor is the six-band imager on INSAT-3D.