TRACKING WILDLIFE BY SATELLITE 



29 





300 



250 



i 200- 

 (u 

 CO 



150 



Beaufort Sea 

 Chukchi Sea 



100 



8 



4-> 



I 50 



M 



O 



Fig. 27. Time spent in salt water during each month by two polar 

 bears one in the Beaufort Sea, and one in the Chukchi Sea as 

 determined by saltwater sensors. 



Argos's Location Class Zero 

 (LCO) Service 



The Argos Location Class Zero (LCO) service can be 

 used by those who wish locations to be estimated when 

 normal processing fails. Even if the number of locations 

 estimated by normal processing is deemed sufficient, LCO 

 processing can be useful because it allows the user to 

 evaluate the performance of individual PTT's by seeing 

 the causes for normal processing failure (see Table 3) and 

 indices of the signal strength as received by the satellite. 

 Alternate location estimates are provided by Argos in LCO 

 processing, which can be used in place of the normally 

 processed location in those rare instances when the two 

 have been reversed. (Reversals have occurred for less than 

 0. 1 % of locations received by our projects during the past 

 six months.) 



We had few data to assess the precision of the new 

 animal-tracking service using PTT's at known locations. 

 We obtained 85 location estimates processed under LCO 

 from PTT's used for testing during June 1 988. Of the total, 

 64 were classified as acceptable by Argos under their LCO 

 criteria, and thus were displayed as LQO locations in the 

 normally received files. Mean and median errors were 

 5. 14 and 2.89 km, respectively. For comparison, mean and 

 median errors from 323 normally processed location esti- 

 mates from the same PTT's during the same period were 

 1.03 and 0.61 km, respectively. 



Precision was highest for LCO location estimates with 

 the highest LI indices (i.e., those barely failing the criteria 

 for normal processing). For example, location estimates 

 with LI indices 5 and 6 had mean and median errors only 

 slightly greater than normally processed location esti- 



mates with LQ = 1 (Table 15). As expected, locations 

 failing to meet Argos's criteria (and thus appearing only in 

 the separate data file) had considerably greater error. 



Investigators who wish to increase sample size of loca- 

 tion estimates may include LCO locations with pro- 

 gressively lower LI values but will progressively increase 

 the error of the resulting data set. Tradeoffs may be made 

 between increasing sample size and decreasing precision. 

 Table 16 summarizes the LCO locations, and within those, 

 the proportion in each of the LI categories from our pro- 

 jects (except caribou, for which we did not use LCO proc- 

 essing) from February through September 1988. 



As stated previously, assessing error in locations esti- 

 mated from PTT's in test situations can be misleading; 

 errors are more likely to be greater when PTT's are ac- 

 tually deployed on animals. For example, 14 LCO location 

 estimates of free-ranging elk at known positions in Yel- 

 lowstone National Park had a mean error of 16.65 km 

 (median 12.7 km), more than five times the mean error 

 from normally processed location estimates during the 

 same period. In another example, normally processed lo- 

 cation estimates of a muskox during January 1988 were 

 compared with the entire set of locations, which included 

 those processed by LCO (Fig. 28). This animal was known, 

 from midwinter aerial tracking, to be restricted to a small 

 home range (P. Reynolds, ANWR, personal communica- 

 tion, 1988). The apparent home range of the animal was 



Table 15. Mean and median errors of locations calculated 

 using normal processing (LQ 1,2, and 3) and Argos's 

 LCO processing. All data are from third-generation 

 platform transmitter terminals (PTT's) at known loca- 

 tions on Kodiak Island, Alaska; PTT's were not de- 

 ployed on animals. No locations classified LI 6 or LI 9 

 were obtained. 



