How weather satellites see the weather
From clouds at night to sea temperature and typhoons: what weather satellites measure, why some hover and others circle the poles, and how their images reach your forecast.
Two kinds working together
Geostationary weather satellites such as Korea's Chollian, Japan's Himawari and the US GOES watch one hemisphere continuously from 35,786 km, taking a new image every few minutes; that is how forecasters follow storms as they grow. Polar-orbiting satellites such as NOAA, MetOp and Fengyun fly about 800 km up and cover the whole Earth twice a day in finer detail, including the poles that geostationary satellites barely see.
Seeing more than clouds
Their instruments look in many wavelengths, not just visible light:
- Visible: clouds and snow in daylight, like a photograph.
- Infrared: the temperature of cloud tops and the ground, by day and by night; cold, high cloud tops mean strong storms.
- Water vapor: moisture in the middle atmosphere, even where there are no clouds, which shows the large-scale flow of the air.
- Microwave sounders on polar satellites: temperature and humidity at different heights, fed directly into forecast models.
Typhoons and dust storms
For Korea, geostationary images are essential for tracking typhoons approaching from the south, measuring their size and the coldness of their cloud tops to estimate strength. Chollian 2B also carries an instrument that monitors air pollution and yellow dust over Asia.