A man-made constellation in the night sky

Thanks to a ring of satellites operated by Europe, USA, Japan, China, India, Russia and South Korea we now have large-scale coverage of the Earth and an insight into how our complex weather patterns are changing hour-by-hour, day-by-day and year-by-year, says Dr Simon Keogh who leads the Met Office Satellite Data Products and Systems group. This is the second part of Simon’s blog series on satellites, which began yesterday.


Global composite image made from European, American and Japanese geostationary satellite imagery.

To space experts a major group of satellites are known as geostationary, because they appear to be stationary in the sky, always staring down at us from the same position day and night. However, they are way up at about 36,000km (22,000 miles) above the Earth, so there are limitations on how much detail they can resolve from such a great distance. Nevertheless, these satellites are considered to be the workhorse satellites of the modern meteorologist, giving a panoramic view of what’s happening with our changing weather nearly everywhere on Earth – apart from over the poles.

Complementing this ring of geostationary satellites are many polar-orbiting satellites. These polar-orbiting satellites circle the Earth at a height of around just 705km (438 miles) and, as their name suggests, can provide detailed observations of the polar regions as well as other parts of the globe. They’re very much closer to Earth than geostationary satellites, which mean they can also be used to take close-up measurements of the atmosphere, revealing its detailed three-dimensional structure.


The A-Train of satellites (image courtesy of NASA).

One particular example of these polar-orbiting satellites is the ‘A-train’ of satellites operated by NASA. Each of these satellites orbit in quick succession, just a few minutes apart. Each satellite in the train yields a complementary view when compared to its successor and predecessor.

Tomorrow, the next post in Simon’s four-part series will examine the impact of weather satellites on our safety and security.

Dr Simon Keogh leads the Met Office Satellite Data Products and Systems group. He is a member of a United Nations WMO expert team on Satellite Utilisation and Products and is the UK delegate to EUMETSAT’s Operations Working Group.



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