Temperature is measured by a therm- 

 istor composite which is pressure 

 protected in a thin-wall stainless steel 

 tube. The thermistors' conductance is 

 measured by an "operational trans- 

 conductance amplifier" (OTA) whose 

 output is gated by the digital signal 

 from the pressure sensor. The output 

 of the OTA drives a capacitor which 

 serves as a temperature-reading mem- 

 ory. It is also followed by an insulated- 

 gate FET whose high input impedance 

 prevents memory discharge. 



These two voltage analogs are con- 

 verted to frequency analogs by voltage 

 controlled oscillators (VCO). The fil- 

 tered outputs of the VCO's are 

 summed and the resulting composite 

 fed to the amplitude modulator of the 

 3-watt peak transmitter. 



A programmer is also included to 

 provide a 4-second data transmission 

 time when the animal first surfaces 

 followed by a series of short pulses 

 which are adequate for the tracking 

 system. A seawater connection be- 

 tween the antenna tip and the instru- 

 ment case generates a delayed reset 

 for all capacitor memories and the 

 programmer. 



In the package used on the yearling 

 gray whale two batteries were included 



Figure 2. — Photograph of the Ocean Applied Re- 

 search Corporation data transmitter Model WDT- 

 920 attached to the Sea World yearling gray 

 whale (Gigi) just prior to release. (Photo courtesy 

 of J. S. Leatherwood.) 



Figure 3. — Aerial photograph of lest animal taken on 16 March 1972. as she was swimming through 

 kelp beds off San Clemente, California. (Note kelp trailing behind the transmitter package.) (Photo 

 courtesy of J. S. Leatherwood.) 



in the system. One had a capacity of 

 1.^ ampere hours and was used to 

 power all electronics which were on 

 when the animal was at the surface. 

 The second, smaller, battery, which 

 had a 1.2 ampere hours capacity, 

 powered the depth and temperature 

 instrumentation continuously. The ex- 

 pected life of the smaller battery was 

 approximately I month while the 

 larger battery with its greater capacity 

 and reduced duty cycle should con- 

 tinue to provide tracking transmis- 

 sions for as much as 9 months. The 

 entire system packaged and attached 

 to the whale is shown in Figure 2. 

 During the first month of operation. 



V 



'/, WAVE 

 MARINE ANTENNA 



BAND 

 PASS 

 FILTERS 



TAPE 

 RECORDER 



Figure 4. — Block diagram of the telemetry data 

 receiving and recording system. 



performance of the Instrument/Bea- 

 con package was satisfactory with the 

 notable exception of transmission 

 range which was initially more than 

 25 miles. Subsequent tests indicate 

 that the antenna, which is a top loaded 

 stainless steel whip antenna, had sus- 

 tained some damage. The animal was. 

 on two occasions, observed swimming 

 through kelp and kelp was seen hang- 

 ing on the antenna. Figure 3. Cali- 

 fornia gray whales are also known to 

 rub on the bottom, a behavior which 

 could have abraded or even severed 

 the loading coil from the antenna, 

 drastically reducing its radiation ef- 

 ficiency. The estimated useful range 

 of the damaged system was on the 

 order of 10 miles. 



The original antenna design em- 

 ployed on beacon transmitters for ma- 

 rine mammals (specifically porpoises) 

 was an adaptation from a design which 

 had been in use for some time on 

 radio beacons used for the recovery 

 of oceanographic instruments. It con- 



54 



