|Satellite pass times (EST)|
POES is an acronym for Polar-Orbiting Operational Environmental Satellite. These satellite images are unlike the usual images that you see on our broadcast which emanate from the GOES series of satellites. GOES also is an acronym which stands for Geostationary Operational Environmental Satellite. These are located above the equator at an altitude of 22,240 miles and orbit at the same speed the earth rotates which makes them stationary to a position of the earth, hence the name "Geostationary."
The POES are in a much lower earth orbit (LEO) and orbit from the north pole to the south pole to the north pole at an altitude of 505 to 700 miles above the surface. Their orbital period is about 101 minutes and will pass over a certain location twice a day.
The advantages of the POES are the better resolution of any particular image area and the ability to view the polar region which are not visible to the GOES spacecrafts. Also, the ability to monitor sea surface temperatures are greatly enhanced by POES measurements.
Currently, there are several operational polar orbiting weather satellites, NOAA-12, NOAA-15, NOAA-16. (A fourth NOAA satellite, NOAA-17, is scheduled to be launched in June, 2002). The NOAA series are maintained by the U.S. government and transmit both in daylight and nighttime passes. At our location the picture starts from around Hudson Bay and cut a swath over Savannah to about 100 miles into South America just north of the equator.
Types of products
There are two types of satellite transmission of images, "Automatic Picture Transmission" (APT) and "High Resolution Picture Transmission" (HRPT), images from the Advanced Very High Resolution Radiometer - AVHRR (which is, more-or-less, the camera). The APT product is derived from a portion of the whole AVHRR product with a spacial resolution of 4 kilometers usually displaying an image from channel 2 side-by-side an image from channel 4. At night, channel 2 is usually replaced by channel 3. The HRPT display involves all five channels of picture transmission with a much higher spacial resolution of 1.1 kilometers.
Anyone who has a personal computer can receive direct APT images from the satellites. All it takes is to have a radio that receives 137.300-137.850 MHZ signal, a simple antenna (with no moving parts and is mounted easily on the roof), a pre-amp to amplify the incoming signal and a demodulator (sound card) to capture the signal as a wave file and conver it to an image on your computer. It is a bit more difficult and expensive to receive HRPT products. This involves a special radio to receive the 1.7 gigahertz signal, a special 1 meter parabolic dish antenna with feed horn and LNA, a special tracking device to follow the spacecraft as it crosses the sky and software to properly display the product. File size is of concern as well. One wave file from the APT transmission for a full overhead pass is about 7 megabytes of size while the same transmission of HRPT is about 80 megabytes in size.
On the NOAA series satellites, the images are observed in five different wavelengths of light from the Advanced Very High Resolution Radiometer - AVHRR. Two of the channels (ch 1 and 2) are in the visible spectrum, one (ch 3) in the near visible and two (ch 4 and 5) in the infrared. The APT transmission displays only two of the channes while the HRPT reception displays all five channes. Channel 3A is for daytime while 3B is used at night. 3B is also useful in depicting fog at night. Below is a table from NOAA explaining the values of the different channels. from the AVHRR
This is a great tool for the amateur meteorologist (or the professional as well) to follow the weather but also, there seems to be a certain romance involved with this in tracking the satellite, receiving and processing the data and then seeing the finished product. It is fun to watch the data coming in line by line on my computer while listening to the beep beep beep of the satellite transmission. Then there is that romance to see the different weather conditions on the finished product; types of clouds and moisture steaks, storms, rivers and lakes (over cloud free regions), coastline features and even volcanoes. Fog and snow on the ground show up clearly in these images. At night, a special infrared channel allow to observe with a high degree of accuracy the land and sea surface temperatures, which in this area is a great tool to observe the position of the gulf stream and measure the ocean and river temperatures.
Currently, I am using the "R139 Weather Fax" crystal controlled radio receiver by Hamtronics. At the TV station we use the Vangaurd turnstile antenna with a GaAsfet Preamp mounted on the roof of the studio using 150 feet of Belden 9913 50 ohm coaxial cable. At the house, I use the Woodhouse APT 4X4 8 element 7 foot yagi along with the Yaesu 5500 tracking device using 40 feet of RG-8 coaxial 50 ohm cable and the GaAsfet preamp. (The preamp's 137 mHz filter cleaned up some noise interference that I was receiving on NOAA-15 and also has boosted the signal somewhat.)
Important... be sure to use a 50 ohm cable for best results. No use skimping a few cents on cable after spending large amounts of dollars for equipmnet. The image will not be its best if the signal is degraded by going through sub-satisfactory cable.
Software used to capture the signal is Christian Bock's wxsat V2.5 rev9, which is execellent. Also, David Talylor's Satellite Tracker and Ground Image Generator (WXtrack) is used for gridding. I use several popular graphic programs to color proccess the images.
The total cost (not including the computer, sound card or Yaesu tracker) was around $450 for all the of equipment needed to receive these images using the omni antenna.
Additional information about POES can be found at NOAA Satellite Information System for NOAA Meteorological / Weather Satellites.