SVP Barometer Drifter Message Format

Scripps Institution of Oceanography
La Jolla, CA 92093-0230
Andrew Lowy Sybrandy
(619) 534-0378

 

Barometer Data Record:

A data record reports twelve archived hourly pressure samples, the most recent pressure, sea surface temperature (SST). instrument status and checksum.


Argos Message Format:

The barometer data record is divided into two 128 bit Argos messages (page 0, and page 1). Each message consists of seven bytes of header data followed by nine of eighteen bytes of archived pressure data for a total of 16 bytes per message. The header data include most recent pressure, sea surface temperature (SST), instrument status and checksums. The archived pressure of page 0 are pressures with ages of 2, 3, 6, 8, 10 and 12 hours relative to the most recent pressure sample. The archived pressure of page 1 are pressures with ages of 1, 4, 5, 7, 9 and 11 hours relative to the most recent pressure sample.

Transmission sequence is Page 0 followed by page 1.


Datum Formats:
Pressure:                (Pressure (mB)  10) - 8000   Range 805 to 1209.5 mB

SST:                        Manufacturer Specific (-2 to 38C; 0.1 resolution)

Battery Voltage:      ((Current Battery Voltage  New Battery Voltage)  300) - 75

Drogue Sensor:       Manufacturer Specific (0-255)


Header Data:

Each message begins with 7 bytes of header data in the following format:

Transmission Checksum (8 bits)
Least significant 8 bits of the sum of the last 15 bytes of message.

Most recent hourly pressure sample (12 bits)

Sea Surface Temperature (10 bits)

Age in minutes (6 bits)
Time difference in minutes between most recent transmission and most recent pressure sample. Resolution 1 minute.

Drogue sensor (8 bits)

Battery Voltage (8 bits)

Message ID (4 bits)
2 bit repeated 2 times: (0000 Page 0, 0101 Page 1).


Archived Data:

Page 0 archived data are 9 bytes in the following format:

6 - 12 bit pressure sample for ages 2, 3, 6, 8, 10 and 12 hours

Page 1 archived data are 9 bytes in the following format:

6 - 12 bit pressure sample for ages 1, 4, 5, 7, 9 and 11 hours


General Sampling Specification:

Hourly data are sampled hourly without regard to the transmission schedule. "Age" is the time elapsed relative to most recent sample.


Specification for Hourly Pressure Measurements:

Hourly pressure sample is derived from 160 pressure measurements taken at approximately one sample per second.

Despiking Algorithm: Take the median of the lowest 10 points of 160. Then calculate the median of the points within the entire set of 160 points that are within 1 mB of the 10 point median.

If 15 or more of the 160 samples include communication errors, the sampled set is deemed corrupt.

A corrupt hourly pressure is transmitted as zero.

Counts 1 to 4 are error flags as specified by manufacturer.


Specification for 15-minute SST Measurements:

15-minute SST sample is derived from the average of 15 temperature measurements taken at one sample per minute. SST is updated every 15 minutes.

 
Posted February 27, 1997