TRACKING WILDLIFE BY SATELLITE 



Table 2. Location quality indices (LQ) and their precision according to Argos. Precision is the standard deviation of the 

 distribution of locations that is, 68% of a series of locations would be expected to fall within this distance (adapted 

 from LeTraon 1987). 



messages for overpasses that yielded location estimates of forming on the antenna could break the tip. However, loss 

 free-ranging caribou in northern Alaska, 1987-88.) of signal strength and data can occur when the tip of the 

 Messages identify each PTT to the Argos system, then are antenna does not protrude from the collar, 

 used by Argos to estimate the PTT's location. Messages Most PTT's are powered by three D-size lithium bat- 

 may also include coded information relayed from sensors teries and include sensors to measure internal PTT tem- 

 measuring temperature, motion, pressure, and so perature and detect motion. VHP transmitters can also be 

 forth. It is not possible to locate a PTT directly from the attached to collars for relocating the animal using conven- 

 ground or air using these ultra-high frequency (UHF) tional telemetry, serving as a backup incase of premature 

 messages (i.e., avoiding computer-assisted analysis of the PTT failure. Most users have routinely added VHP trans- 

 messages), mitters to retrieve PTT's on animals because it is generally 

 Most collars we used on caribou, Dall sheep, and moose not possible without them, and refurbishing PTT's for 

 had all PTT components (except for the antenna and VHP reuse is cost-effective. 



transmitter) enclosed within a hermetically sealed metal PTT's used for walrus are 18 cm long (not including the 

 canister resistant to prolonged immersion in water. Canis- antenna) and 7 cm in diameter, and they weigh 720 g (for 

 ters are attached to adjustable collars 5- 10 cm wide, which comparison, VHP transmitters in the identical housing 

 remain pliable to -40 C. The UHF antennas are approx- weigh about 500 g). The packages are protected from 

 imately 15 cm long and are sewn within the collar or pressure and mechanical abuse by stainless steel tubes 

 protrude approximately 4 cm from the collar. The fully having the antenna and sensors mounted on one end. Pack- 

 encased antenna has been used on polar bears, because ice ages are attached to one tusk with epoxy and two stainless 



Table 3. Location indices (LI) used by Argos to label locations estimated under LCO processing. 



