NOAA ship Discoverer 
Ancillary Data 
Reduced and Compiled by NOAA-PMEL 
Version 1, 26 March 1996 
Jim Johnson and Tim Bates 
 
Data File 95SW30.CSV contains the following parameters: 
 
DOY 
Latitude 
Longitude 
Ship's speed 
Ship's heading 
SST 
Salinity 
Nitrate 
Chlorophyll 
 
DOY: 
The data are compiled in 30 minute averages from 15 minutes before to 15 
minutes after the half hour.  The time is given as decimal day of year (DOY) 
such that DOY 32.5 is 12 noon GMT on February 1. 
 
Ship position: 
The ships position was recorded on the PMEL data logger from the PMEL 
Trimbal GPS unit. The latitude and longitude are each even 30 minute points 
with no averaging.  For those times when there were no data at the 30 minute 
point, a point was taken from the Discoverer's SCS data system file.  Units 
are decimal degrees north for latitude and decimal degrees east for longitude 
(200 degrees east = 160 degrees west). 
 
Ship's speed and heading: 
The heading (compass degrees) was taken from the ship's gyro which was 
recorded by the Discoverer's SCS system.  For the times when the SCS 
system was not working, the heading was taken from the PMEL GPS course.  
The GPS course and the gyro heading usually agreed within several degrees 
as long as the ship was moving forward through the water at speeds above 5 
knots.   The ship's speed (knots) was taken from the PMEL GPS system.  
Both the speed and heading were averaged from the one minute data to make 
the 30 minute averages.  The speed was averaged directly, the heading was 
separated into N and E components by taking the sin and cos respectively of 
the heading.  After averaging the N and E components into 30 minute bins, 
the heading was recalculated by using a 4 quadrant arctangent function. 
 
Seawater temperature and salinity: 
Seawater temperature and salinity were measured with the ship's 
thermosalinograph (Seabird SBE-21 serial number 843) and recorded on the 
ship's SCS system.  The instrument was calibrated by the NW regional 
Calibration Center on 10/11/95 just before the cruise.  The instantaneous one-
minute data set from the ship was very clean and required very little editing.  
Temperatures are reported in degrees C.  Salinity data are in practical salinity 
units (psu). 
 
Nitrate: 
Water from the ship's underway pumping system (5 meter depth, bow intake) 
was run through the underway autoanalzyer system to measure surface nitrate 
+ nitrite concentrations. The instrument samples at 10 minute intervals: 
seawater, blank, seawater, blank, standard, blank; repeating this sequence 
each hour.  The instrument was started on DOY 295 (after Hawaii) and 
worked well throughout the remainder of the project.  Data are marked with 
either a concentration, 0 (indicating below detection limit), or -99 (when there 
were no data). The lower limit of detection was generally 0.05 micromolar 
but was as low as 0.02 micromolar at times.  All data reported here are in 
units of micromoles per liter. 
 
Chlorophyll: 
Discrete chlorophyll samples were collected every four hours while underway 
from the ship's seawater sampling line.  The inlet is located approximately 5 
m below the surface at the bow of the ship.  Chlorophyll samples were also 
collected at each sampling depth at each station.  Samples were collected 
(530 ml), immediately filtered, put into 10 ml of 90% acetone, and frozen by 
ship's survey department.  The samples were analyzed within 3-4 days aboard 
ship with using a Turner fluorometer.  The fluorometer was calibrated after 
the cruise using chlorophyll 'a' from the Sigma Chemical Corp.  The data are 
reported in units of micrograms per liter.