NOAA 15, NOAA 14 and NOAA 12 are US polar orbiting weather satellites. Polar means they orbit North-South and South-North (ie: over the poles) as opposed to the Geostationary satellites which orbit along the equator. The satellite pictures you usually see on the TV weather reports are from the Geostationary satellites. The polar types are in much lower orbits, much closer to where all the action is.

The NOAA satellites transmit continuously on 137.620MHz (NOAA 14) and 137.500MHz (NOAA 15 and 12) in a format called APT (Automatic Picture Transmission), as well as on 1.698GHz or 1.707GHz at higher resolution in digital format (HRPT - High Resolution Picture Transmission). One orbit takes just over 100 minutes. The craft is within range for just over ten minutes during direct overhead passes, or less if the pass is not directly overhead. The APT image displays two pictures side by side - a visible light and an infra red image in the daytime, and two different infra red images during night time passes.

The satellite doesn't transmit in colour. To make a colour picture, the visible light image and the infra red image must be combined using a graphics editor program, and adjusted for the most pleasing result.

Here's an example of a raw daytime APT image from NOAA 14. It's been scaled down from 2400 pixels wide to 800 for ease of viewing.

The satellites are often visible to the naked eye during dawn and dusk passes. It's quite something to be standing outside, looking up in the sky at a craft not much bigger than a car, being able to see it (as a moving point of light), knowing it's about 1000km distant. That's about as far as Brisbane to Sydney!