FISH AND WILDLIFE TECHNICAL REPORT 30 



Table 4. Specifications of Argos-certified transmitters built by Telonics, Inc., for terrestrial mammals. 



Transmitter generation 



steel straps attached to a bracket on the side of the pressure 

 housing. 



Several types of sensors may be used on PTT's. Except 

 for walrus and polar bear PTT's, each message we re- 

 ceived included a measure of the internal temperature of 

 the PTT and two counts generated from a mercury tip- 

 switch that served as a motion detector. The counts report- 

 ed the number of seconds in which movements were de- 

 tected during the previous minute and the number of sec- 

 onds in which movements were detected during 24 h. The 

 latter served to indicate animal death. The temperature 

 sensor produced counts that were calibrated to tempera- 

 ture (in degrees Celsius). Walrus PTT's incorporated sen- 

 sors to detect salt water and pressure (for measuring depth 

 of dive). Similar sensors have been used in studies of 

 whales (Mate et al. 1983). Saltwater switches can also be 

 used with diving animals to prolong battery life by pre- 

 venting transmission when the PTT is underwater. Salt- 

 water switches were used on two polar bear PTT's to 

 record the amount of time spent in the water during each 

 72-h period and the number of times each bear entered the 

 water for at least 5 s during the 72 h. 



Telonics, Inc., has developed a portable data-verifica- 

 tion (uplink) receiver that can be used to receive sensor 

 information directly (Beaty et al. 1987), eliminating the 

 need to access the Argos computer system when testing 

 sensors. The unit receives signals within line-of-sight dis- 

 tances of about 1 .6 km. 



Battery weight is the primary determinant of the total 

 weight of a PTT. Tradeoffs between the life of the trans- 

 mitter and the rate at which messages are sent are unavoid- 

 able because of the need for relatively high power output 

 (e.g., over 50 times that of a VHP transmitter) and for a 

 lightweight package that can be carried by an animal. For 

 example, a Telonics third-generation PTT transmitting 

 once per minute will operate for approximately 3 months. 

 However, if the PTT is programmed to transmit during a 



6-h period every 4 days, the expected battery life increases 

 to 24 months, although fewer locations and sensor data 

 will be obtained on an average day. Cycling of transmis- 

 sion periods is referred to as a duty cycle. 



Optimum duty cycles are determined by study objec- 

 tives and by the timing and elevation of satellite passes 

 over the study area. Because the duty cycle is programmed 

 within components sealed inside the canister, duty cycles 

 must be specified when placing an order for transmitters. 

 PTT's produced by Telonics allow the user to specify up to 

 four periods, or seasons, each of which may have a unique 

 duty cycle. For example, the PTT may transmit for 18 h 

 each day for the first month of operation (30 days of 18 h 

 on-6 h off); followed by 3 months of 6 h every other day 

 (90 days of 6 h on^2 h off); followed by 6 months of 6 h 

 every four days, but with the transmission times falling 

 back in time by 2 h each day, so that eventually all hours 

 are sampled (180 days of 6 h on-98 h off); and then 

 returning to the second duty cycle for the remainder of 

 battery life. The entire sequence begins when the user 

 removes the magnet from the outside of the canister. 

 Should the magnet be replaced and removed again, the 

 sequence restarts from the first period. 



The characteristics of satellite orbits result in an un- 

 equal distribution of satellite coverage each day. Figure 3 

 shows how the timing of overpasses varies among study 

 areas with the current satellites, NOAA-10 and -11 (see 

 also Fig. 35 for empirical data for NOAA-9 and -10 over 

 Yellowstone National Park). There are generally times 

 when overpasses are infrequent, particularly around local 

 midnight. These gaps in satellite coverage are longer at 

 lower latitudes, although in all cases are less of a problem 

 than existed with previous satellites. With the launching of 

 the newest satellite (NOAA-1 1), coverage during the day 

 has become more even (compare Fig. 3 with Fig. 25 in 

 Fancy et al. 1988). 



Satellite overpasses in any area may be analyzed using a 



