Low Earth Orbiting Weather Satellites

APT (Automatic Picture Transmission)

APT (Automatic Picture Transmission) imagery from polar orbital weather satellites offers high quality with tremendous detail. Unlike the Geostationary satellites which are 22,000 miles out in space, the LEO (Low Earth Orbit) satellites used for APT are at an average of 500 hundred miles above the earth's surface. The NOAA series of satellites travel at about 17,000 mph, sending a line by line image of what is below the satellite. This close-in view offers tremendous detail, with a resolution of about 3 miles. You can see cloud formations, storm fronts, the jet stream, lakes, rivers and on a good day, possibly a roadway. Both natural daylight and infrared-red imagery offer detailed information, including the ability to determine the temperature of any area within the image. Some satellites now include radar imaging which offers a new level of detail.

APT satellites give about 12 good images a day, wherever you are in the world. The resolution is 4km per pixel and there are visible and infrared sensors. This is a simple system where the satellite is in low earth orbit and very easily received at 137MHz. The two frequencies in main use are 136.50 for NOAA 12 and 15 and 137.62MHz for NOAA 14 &17. A simple crossed dipole antenna can be used, or a more elaborate (QFH) Quadrifilar helix antenna. These simple omni-directional antennas do not need moving or tracking to receive the satellite. The satellite is so strong that when is about 20 degrees above the horizon perfect results will be obtained.

As this is the lowest cost entry into weather satellites, a lot of people have asked if they could use their "scanner" that they use for monitoring other transmissions. There are two problems with using receivers not specifically designed for weather satellites. The first and most important is bandwidth, a APT signal needs about 40kHz of bandwidth, between 30 and 50 is OK. Most scanners have 15KHz which is far too narrow and 180kHz or more which is far too wide. Only a few scanners have the correct bandwidth and these currently include the AOR5000 and Icom IC-PCR1000. The second problem with all scanners, including the ones mentioned, is that a weather satellite system needs a very good performance receiver, one that provides high sensitivity, good signal to noise ratio and high immunity to other adjacent transmissions. So, you may get your scanner to work, but it will not provide the results you see in colour brochures.

If you share an interest in weather, geographic or environmental issues, you can view the earth from space in real-time, directly from the imaging source. For around only £100 pounds plus your existing PC, you can assemble a receiving system for earth and atmospheric imaging with a direct link to the originating satellite. Public domain imaging software is available at no charge to you. Direct from the source, imaging offers the highest quality images which are received in real-time, so they are current.

Satellite access is available to everyone, everywhere. No access limitations, no internet, no phone lines, no modems, no charge! Even mobile operation is practical; so if you are participating in an event, on an expedition, on your boat, or on vacation with your family, you still can have access to current information.

Current APT images of the UK & Europe can be viewed throughout the day at the Skylink Weather Site.