The Technology: How Does It Work?
Global Positioning Systems (GPS) mounted inside a tracking collar and combined with a satellite communication transmitter provide invaluable information on elephants' locations and movements. The satellite GPS collars used in Myanmar and Sri Lanka use the most advanced technology to track the geographic location of the collared elephants. This technology allows locations to be collected anytime of the day without the need for difficult, expensive fieldwork.
The GPS satellite collar consists of a GPS device, internal aerial, transmitter, and battery. A counterweight on the collar ensures that the functioning parts of the unit stay on top of the elephant's neck to allow a clear path of reception for the satellites. The entire collar weighs about 30 pounds, a minimal weight to carry for a three-ton elephant.
The satellite collars use GPS to determine the geographic location of the elephant. GPS technology is based on a constellation of 24 satellites in orbit around the Earth. By locating and communicating with four or more of these satellites, a GPS unit can locate itself on the surface of the planet. GPS can be used to determine exact geographic location with an accuracy that is much higher than can be achieved with a map and compass. The accuracy of positions determined with a GPS can range between +/- 1 m and +/- 300 m.
Currently, each satellite collar collects GPS positions every four hours and stores them in its memory. The unit then transmits this location data back to one of several weather satellites in orbit around the Earth. This information is forwarded automatically via email to the Zoo's Conservation GIS Lab at the Conservation and Research Center in Front Royal, Virginia, for analysis.
Even though the weather satellites pass over regularly, transmissions are not always successful because dense forest canopy and mountainous terrain block the radio signals. While plenty of data points are recorded via the satellite, researchers also have another option at their disposal for finding the elephants: Each satellite GPS collar also contains a conventional VHF transmitter that can be used to track the elephants on the ground.