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National Oceanic and Atmospheric Administration
Atmospheric Chemistry Group

NavWind Notes

Notes on the CalNex- RV Atlantis 1 second, nav, and wind data file.

Ship's Position (Latitude and Longitude, COG and SOG) :

The PMEL GPS was used as the primary data source. The SSSG data were used for periods when the PMEL data system was down. Course Over Ground (COG) is the direction the ship was moving, in compass degrees (not necessarily the direction the ship's bow was pointing). The Speed Over Ground (SOG) is the speed the ship was moving, in knots.

Gyro:

The Gyro is the direction the ship's bow was pointing in compass degrees (not necessarily the direction the ship was moving).  The primary source for this data was the PMEL GPS compass (SI-TEX Vector Pro).  When data from the primary source were not available the Ship's Gyro compass from the the SSSG data files was used.

Relative Wind:
The primary source for the relative wind data was the PMEL Vaisala  WX520 sonic anemometer that was located on the aerosol sampling mast. For periods of missing data from the PMEL data source the ships starboard WX520 sensor at the bow IMET tower was used. We assume that the relative wind information is primarily used to determine periods of ship contamination, thus we are using the anemometer that is closest to the sample inlet. This anemometer also was used as an input to the algorithm that turned off the sample pumps during periods of ship contamination.) The ship's WX530 data came from the 30-second underway data files and the orthogonal components (of "keel" and "beam") were separately interpolated onto the one-second time axis. These one second components were then recombined to make the final 1 second relative wind vectors. Relative wind speed (relWS_m/s) is reported meters per second and relative wind direction (relWD) is in degrees with -90 being wind approaching the ship on the port beam, 0 degrees being wind approaching the ship directly on the bow, and +90 degrees being wind approaching the ship on the starboard beam.

Wind Components/ True Wind Speed/ True Wind Direction:
True wind speed and direction were calculated from measurements obtained with the Ships IMET wind sensor. This sensor was mounted 19.5 meters above the sea surface on the ship's meteorological sampling mast at the bow and should be less affected by bending of streamlines as the air moves over the ship. (The PMEL "Skyvane" was on the top of the Aero-Van and in the 'perturbed airflow'.) The true North and East components of the wind vector from the 20 second SSSG data were calculated and interpolated onto the one-second time axis. These one second components were then recombined to make the final 1 second true wind vectors, given as true wind speed (trueWS_m/s) in m/s and true wind direction (trueWD) in compass degrees. There were several occasions when the SSSG data were not available, in that case the PMEL "Skyvane" winds were used.

Atmospheric Chemistry Group PMEL