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Where are they now? Track them yourself using the map!
Satellite tracking of wildlife is an advanced technique for monitoring movements of wild animals. It is an ideal way to monitor the movement of birds, such as bald eagles. In the past biologists have relied on bird banding data to monitor bird movement. Bird banding provides valuable general information about where the birds go, but the data can only be collected when birds are visibly seen by biologists or recovered in the wild. Satellite tracking allows biologists to track daily movements of birds even when the birds are in remote locations and can not be seen. This will allow us to obtain more specific information about the daily patterns of eagles.
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 Eagle #24129 wearing the transmitter. |
The transmitter being fitted for one of the eagles.
 Note the small size of the actual transmitter. |
 The Argos Satellite (image courtesy of the U.S. Air Force. |
The transmitter (properly called a platform transmitter terminal, or PTT) is attached to the bird. The PTT is programmed to transmit on a set duty cycle (we selected the duty cycle when we made the PTTs). In this case, the 80 gram PTTs are transmitting 8 hours ON and 44 hours OFF forever. The solar PTT is transmitting 6 hours ON and 14 hours forever. The PTTs transmit whether or not a satellite is overhead. The satellites pass over about every hour or so. So as you can see, if the PTT is transmitting for 6-8 hours at a time, it should be able to uplink its signal to the satellites at least several times during each ON cycle. When they are in an ON cycle, the PTTs are transmitting a signal every 60 seconds. The satellite must hear at least 3 transmissions during an overpass to provide a location. Each satellite overpass lasts between 4 or 5 minutes to up to 20 minutes, depending on the geometry of the pass. Satellite passes directly overhead last the longest. The footprint of the satellite is appriximately 5,000 km in diameter. The more transmissions heard at the satellite, the more accurate the location provided and the more confident we can be of the location accuracy. The Argos system can provide location estimates as accurate as +/- 150 meters (best case) to several km (worst case), but Argos provides a "location class" with every location estimate. That way, we can know pretty well how accurate each location estimate is.
When the satellite receives a signal from a PTT, it immediately re-transmits the data to a ground station. There are many Argos ground stations all around the world to receive the resulting signals. The Argos system calculates the position of the PTT on the surface of the Earth by a process called Doppler shift.
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