Our Weather Satellites Are Dying

The polar orbiting satellites are the quiet achievers of weather forecasting. Everyone sees the geostationary sat images on TV and think that's it, but there's a lot more going on with the polar sats.

They orbit north/south over the poles at about 800km. They are sun-synchronous (so the sun is always behind them illuminating the earth on their daylight run) and they do an orbit about every 90 minutes or so. The earth turns underneath them as they orbit, so they cover the entire globe. The current POES status is here [noaa.gov]

They transmit a heap of data - the data I receive here in Australia is the APT transmissions, which is 4 x 4 km per pixel resolution images in the visible and IR wavelength, which run constantly. As the satellite clears the horizon, you pick up the signal at two lines per second and about 15 minutes later on a directly overhead pass it sets again and you've got a nice, 2000km x 4000km image of your immediate area, just like if it came off a fax machine. The two wavelengths offered in the analog mode give you a visible image and allow you to read temperatures, so you can find thunderheads and cold fronts, for example. The APT transmissions just require a 137Mhz FM receiver and a simple antenna to pick up, so it's easy to get images.

They also have a digital mode - HRPT - with the entire range of 6 imaging sensors onboard and 1x1km per pixel resolution and you can do a lot with that - highlight vegetation, measure and and sea surface temps, locate and track fires and such.

Onboard there are also charge sensors for measuring auroral densities, and you can visit a webpage [noaa.gov] that shows the current auroral activity. The satellites can also receive, process and retransmit data from Search and Rescue beacon transmitters, and automatic data collection platforms on land, ocean buoys, or aboard free-floating balloons, as well as detect and map the ozone holes that appear yearly over the poles.

Their capabilities completely outclass the geosynchronous satellites and I hope that NOAA gets their act together and back on track with the launches.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/cgGoGs2PS4Q/our-weather-satellites-are-dying

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