Appendix B 

 1990 PTT format and error detection 



INTRO 



Since telemetry is prone to transmission errors, data reliability is 

 dependant on the detection and elimination of these errors. In our data, 

 we have observed that these errors tend to occur in bursts (see Michelson 

 and Levesque, 1985 for a description of burst errors) . When there is no 

 built in method of error detection, circumstantial methods can be used to 

 identify many errors. 



CIRCUMSTANCES 



Many factors influence the occurrence of transmissions. Since the radio 

 frequency we use does not travel through water, the tag only transmits 

 when it is out of the water. However, the tag is positioned on a portion 

 of the body that clears the water with each surfacing of the whale. 



In order to conserve battery power, transmissions occur only during two 

 hours out of every six. 



A further restriction is imposed by the satellite data collection service: 

 no two transmissions from the same transmitter may occur within 40 seconds 

 of each other. This is referred to as "repetition period". The repetition 

 periods for our 1990 transmitters varied from 42 - 52 seconds. 



Not all transmissions are received. In addition to all of the above 

 restrictions, a satellite has to be within reception range of the 

 transmitter. In the study area, a satellite comes into reception range 

 about 14 times a day. The satellite then stays in range for only about 10 

 minutes. These restrictions result in the receipt of an average of 4.8 

 transmissions per summary period. 



The data portion of each 1990 right whale transmission consists of 64 bits 

 containing 6 fields. 



field length (bits) field description 



8 temperature (degrees C) 



16 duration of dive just previous to transmission (seconi 



16 average dive duration during summary period (seconds) 



16 dive count during summary period 



2 failsafe flag 



6 inter-transmission dive count (itd) 



64 



The average dive duration and the dive count are summary data collected 

 over a 6 hour interval (summary period) and transmitted during the 

 following summary period. Throughout a summary period, the transmitted 

 values for these fields do not change. The summary data occupy half of 

 the transmission. 



The temperature, dive duration, and inter-transmission dive count reflect 



155 



