- Weather Satellite Tracking -

American, Russian and Chinese weather satellites circle the earth every 110 minutes or so, following a polar orbit path. In the course of a day each satellite is visible (or are above the horizon) for every point on the earth at least four times - twice when going in a northward direction and twice when heading southward. The satellites scan a section of the earth directly below them with visible and infra-red sensors, then as they continuously move forward they scan again and again in an endless sequence. At the same time as they scan the satellites transmit their observations back to earth so that ground observers can record the outputs of their sensors. We too can record and display this data.

Consider how a black and white television or computer monitor displays its picture. A single point of light is scanned across the face of the display, the light intensity varying with the brilliance content of the applied signal. At the end of a line the point of light skips back to the start of the display, drops below the previous line slightly and scans across again. By continuously scanning, dropping a line and scanning an image is built up which we see on our TV or monitor. This same principle is used by weather satellites to provide us with images of the earth as seen from space.

What is required to capture and view these pictures? In its simplest form, a home satellite tracker needs a receiver and antenna, the ability to store and decode pictures, and the ability to predict when and which satellites will pass overhead. A basic handheld scanner receiver will get you started. Tune it to scan 137.4, 137.62 and 137.8 MHz using your whip antenna. Set it for narrow-band FM and leave it scanning. This very basic setup will at least allow you to hear a satellite's audio data signal. Weather satellites have characteristic sounds - Russian Meteor satellites honk like a goose while US NOAA satellites tick-tock like a grandfather clock. Obviously better quality receivers and purpose designed antennas will improve the quality of reception and the range at which satellites can be heard. From my location in Wellington, New Zealand (about 42 degrees south) I have copied a north-bound satellite rising over the coast of Antarctica until it set near the equator over the Pacific Islands, a pass of about 13 minutes. I was using a homemade quadrifilar helix antenna, an RF notch filter for the satellite band and my Yupitera handheld scanner receiver.

The next issue is to determine when and which satellite will be visible (or audible) at your location. There are many software programs that will allow you to do this as an Internet search on 'Satellite Tracking' will show. For our purpose we will use a NASA Internet site which automatically takes care of such things as keplarian elements, the data used to calculate the position and course of a satellite. Click on the link

  http://liftoff.msfc.nasa.gov/RealTime/JTrack/

and choose the weather satellite option. Then click on the picture of the earth where you are located and see when a NOAA satellite is coming your way.

Now that you have predicted a NOAA satellite pass and can hear its data signal, you need to display it. For this I use a decoding program called WXSat which was written by a very smart gent. It is capable of decoding a lot of other digital modes than those received from satellites, but you can explore those options yourself. You will find WXSat at the link
 
http://www.hffax.de/
 
along with a lot of good info about satellites and radio data decoding. Download the program, install it and have a quick browse of the instructions, but don't get into it those too deeply at this stage. Connect an audio cable from your handheld receiver to your audio sound card and in WXSat select the correct NOAA satellite button. There is NOAA N-S or S-N which corresponds to the satellite travelling southward or northward. For instance, if the NASA's JTrack program showed the satellite coming down from the Arctic region it would be southbound and you would select NOAA N-S. If you get it wrong the picture will just be upside down, so no big issue. All going well, the WXSat program will monitor your sound card, synchronise to the NOAA tick-tock noises and will start to display a picture of the earth line-by line as it comes up over your horizon and down again. 

Once you have mastered reception of NOAA satellites, try Russian Meteors, or by using an HF radio receiver monitor weather facsimile transmissions from around the world. Using other equipment I have monitored Amateur Radio data packets, the MIR space station, Korean newspaper transmissions, many meteorological data signals, and facsimile pictures from radio weather stations. I find out about the latest Space Shuttle flights from NASA.