16 



FISH AND WILDLIFE TECHNICAL REPORT 30 



Fig. 10. Location error for 3 third-generation k _ 



PTT's at the same location on a rooftop dur- O 



ing 10 overpasses. Each group of error bars u_ 



represents a satellite overpass. LLI 



PIT A 



PTT B 



PTT C 



Overpasses 



did differ when both were on captive caribou (z = 3.024, 

 P < 0.003). Thus, it appears that certain PTT's are more 

 susceptible to increased error from deployment on ani- 

 mals; also, animal orientation may influence the number 

 of messages received during an overpass. Transmissions 

 from a PTT on a free-ranging Dall sheep appeared to vary 

 in strength depending on the orientation of the animal 

 (M. Hansen, personal communication, June 1988). 



Accuracy. Mean location estimates from fixed PTT's 

 diverged slightly from the true location, primarily along 

 the longitudinal axis. Fancy et al. (1988) reported that 



Table 9. Performance of Te Ionics platform transmitter 

 terminals (PTT's), three deployed on caribou (Rangifer 

 tarandus) in a small enclosure and three on afencepost 

 adjacent to the enclosure. 



locations from eight of nine test sites displayed a signifi- 

 cant directional bias, with the mean angle always occur- 

 ring in the northwest quadrant. Additionally, they found a 

 significant directional bias (Hotelling's T 2 ,P< 0.001) for 

 their combined data, with a mean angle of 335 data 

 from three fixed PTT's supported these findings. Loca- 

 tions from Nome, Inuvik, and Fairbanks were all signifi- 

 cantly (P < 0.01) biased in westerly directions from the 

 true location (Table 10). 



Fancy etal. (1988) suggested that this direction-specific 

 bias may relate to U.S. Geological Survey topographic 

 maps, which use the NAD27 projection of the earth 

 whereas Argos uses the WGS84 system. For the three 

 data sets, recalculation of location estimates, after con- 

 version from NAD27 to WGS84 (P. Y. Le Traon, Argos, 

 personal communication), resulted in slight improve- 

 ment in accuracy for two, although the resulting bias 

 was still significant (Table 10). However, before and af- 

 ter correcting for different map projections, direction- 

 specific bias was small relative to overall variability. Dis- 

 crepancies between the two map systems were generally 

 < 1 50 m in either direction and were smaller in more south- 

 erly and (or) easterly regions of North America than the 

 locations of these three fixed PTT's (Table 11). Conse- 

 quently, the bias may be unimportant in many wildlife 

 applications. 



To assess topographic influences on location accuracy, 

 44 satellite location estimates from two elk in Yellowstone 

 National Park were compared with visual locations ob- 

 tained at about the same time (20 min). No correlation 

 was found between total error and the slope of the elk's 



