Data is returned in three forms:

The compact "day log" records sunrise and sunset times, water clarity, temperatures at standard depth, and other diagnostic information extracted from each day's observations. This record uses only 12 bytes of memory per day, so a seven-year record can be held in only 30 Kbytes of memory, a small fraction of the available 256 KBytes. Report generator software supplied by NMT will present this record in printable form and generate daily latitude and longitude values from the sunrise and sunset times.

The sunrise and sunset times recorded in the day log are based on data taken every 128 seconds, and are extracted onboard the tag through a process which experience has shown to be very robust and reliable. In controlled tests of position accuracy, observed standard deviation in longitude is ordinarily better than one degree, and the result of averaging a run of positions is ordinarily accurate to a few tenths of a degree. Accuracy in latitude depends on the location and season, and is at best several degrees. Positions reported by tags recovered from free-swimming animals have a day-to-day consistency comparable with these numbers.

In addition to the day log, all data measured during a mission are summarized in a set of data histograms. These histograms provide the answers to questions like "what is the deepest the animal ever dived?", "what fraction of its time was spent below 100 meters (or any other depth of interest, or any temperature of interest)".

Finally, the tag also operates as a simple data logger, preserving a detailed time series record of some portion of the mission. Memory limitations will always prevent the experimenter from preserving a complete record of a long mission with data taken at the finest resolution which might be interesting. Various choices are available to allocate the available time series memory. For a more detailed description see Archival tag operation.

Back to archival tag summary


Northwest Marine Technology, Inc
P.O. Box 427, Ben Nevis Loop Road, Shaw Island, Washington 98286
Telephone (360) 468-3375 Fax (360) 468-3844