Northern Prairie Wildlife Research Center
Stanley M. Tomkiewicz, Jr., Telonics, Inc., 932 East Impala Avenue, Mesa, AZ 85204 USA
Telemetry used to track wildlife has advanced dramatically over the past two decades. While advancements occur continually in existing systems, only rarely does technology come along which radically revolutionizes the way in which we conduct wildlife tracking research. In the early 1980s the Argos system was such a development. By the close of the 1980s, projects on eagles, cranes, geese, and other wildlife applications were underway, and the technology had become an operational tool for tracking the long-range movements of animals. The Argos system will continue to expand through the end of the 1990s and into the next century.
Argos is not the only satellite-based system revolutionizing wildlife research. The newest system to make its debut is the Global Positioning System (GPS). Unlike Argos, the subject animal carries a GPS receiver which receives data from satellites and calculates the position of the subject. GPS presents the potential for increased position accuracy to a level never before possible utilizing a satellite-based positioning system. GPS is based on a time of arrival of signals transmitted from the satellites to calculate the position of a receiver carried by the subject. The GPS receiver is pin-pointed and, therefore, if the subject animal is carrying a GPS receiver, the animal is also positioned.
Multiple approaches for GPS data recovery have been implemented. First, it is possible to store the GPS positions on board the animal for later recovery. In this instance the unit is physically recovered and the data are downloaded. The second approach is to relay the GPS information through direct transmission from a transmitter on the animal to a receiver carried by the biologist. Various modulation formats can be considered, including FM (frequency modulation), AM (amplitude modulation), and PM (phase modulation). The difficulty with this approach is the range limitation.
A third alternative is the use of low polar-orbiting relay satellites to recover GPS information. The NOAA/Argos system is currently being used for this purpose, and represents a highly reliable way of recovering GPS positions from extremely remote locations without the need for having a receiver or biologist present to obtain the information. In this mode, the Argos system essentially becomes a data transfer system as opposed to a positioning system. In addition, the biologist can carry an up-link receiver and intercept the signal transmitted by the Argos transmitter on board the animal and recover and process the data directly.
Development of all these technologies is proceeding, driven by the need to answer new questions posed by the wildlife community. This paper will attempt to describe some of the advances in the technology associated with utilizing GPS to track free-ranging wildlife.