In operation, the tag wakes up every 128 seconds, 675 times per day, and measures internal temperature, external temperature, intensity of blue-green light, and depth (as pressure). Temperatures are recorded at 0.2 degree resolution, depth to 1 M resolution from the surface to 126 meters, then at 3 Meters resolution from 127M to 510 M. Light intensity is measured at a resolution of 15 points per decade over a 5.5 decade intensity range. Wavelength sensitivity is confined to a narrow band near 470 NM, the transmission window of blue ocean water.

All data is also recorded in histograms. There is a counter in the tag corresponding to every possible observed value of every quantity being measured. Every time a given value occurs, the tag increments the corresponding counter. This reports overall statistics of all data, even that which is not preserved in the detailed time series log.

At Universal Time midnight of each day, the tag processes the day's data record correcting the light intensity for absorption with depth. It then extracts features like water opacity, noon light intensity, sunrise and sunset times, and temperatures at standard depths. These extracted features are saved in the "day log".

A 30K block of memory is allocated for a seven-year "day log". If a mission runs beyond seven years, then the day log expands, slowly overwriting the oldest data in the A segment (see below) of the time series log. This guarantees that no daily positions are lost. Only three time-series observations are lost for every day's position overwritten into the A segment.

In order to make best use of the available memory for time series logging, the user may choose the logged time interval to be any multiple of 128 seconds. Data logged at the maximum rate provided will fill the log in 80 days. Logging at greater intervals will fill the log more slowly. For example, logging every seventh measurement interval, four per hour, will allow coverage of 560 days.

The time series log is divided into two parts. The A segment fills up with the first data measured and is fixed thereafter. The B segment fills text, but when it is full, new data overwrites the oldest data remaining in that segment. As a result, the B segment always contains the most recently measured data. The user may choose how the available time series log space is divided between A and B logs.

The wake up rate and position accuracy remain constant independent of choices made for the time series log. All data measured contribute as needed to the daily position determinations, and are entered into data histograms, whether or not it becomes part of the logged time series. Thus both the daily animal positions and data statistics, such as deepest dive, are available an entire mission up to seven years in length. The detailed time series allows more detailed behavioral studies of those days for which it is also available.

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