conditions at the time of transmission. This data changes with each 

 transmission and is referred to as "discrete" data. 



The inter-transmission dive field is a compensation for the repetition 

 period restriction. If the repetition period has not expired when the tag 

 surfaces, no transmission occurs, the inter-transmission dive counter is 

 incremented by one, and the temperature and dive duration are lost. 



The failsafe flag is a warning indicator. Normally the field has a value 

 of zero. However, if the sensors indicate that the transmitter has been 

 submerged for longer than 168 hours (7 days) , this field transmits a 

 special value. It should be noted that none of the transmitters deployed 

 during 1990 meet the conditions necessary for this field to have a value 

 other than zero. Therefore for this field, any non-zero value is an error. 



There is one more useful piece of information provided with the 

 transmission: the time and date the transmission was received by the 

 satellite. While this is not part of the original transmission, the 

 satellite appends it to the transmission and it is part of the record 

 provided by the satellite data collection service. 



Example Data Set: transmissions received over 2 summary periods. 



first 



summary 



period 



second 



summary 



period 



date 



time 

 (GMT) 



12 Sep 90 23:06:57 

 12 Sep 90 23:08:23 



12 Sep 90 23:14:24 



13 Sep 90 05:25:31 

 13 Sep 90 07:02:42 

 13 Sep 90 07:03:26 



<- date and time -> 



of transmission 



< — appended by — > 



the satellite 



< discrete > <- summary - 



< transmitted from the tag 



ERROR DETECTION METHODS: 



Summary data: 



The duplication of the summary data provides an easy method of error 

 detection. If two or more transmissions occurring in the same summary 

 period have the same value for a summary field, then the value is 

 either correct or exactly the same error burst occurred. The 

 probability of identical error bursts occurring in neighboring 

 transmissions is quite low (less than 0.1%) so duplicate values are 

 assumed to be correct. Any other value is an error. If there are no 

 duplicate values, then the summary field cannot be confirmed and is 

 assumed to be in error. 



Additionally, some simple range checking can be performed. Since the 

 minimum duration of a dive is 6 seconds, this is also the minimum 

 value for the average dive duration field. The maximum value for the 

 dive count is 3600: 



max dive count = summary period / minimum dive duration 



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