CTD Data are available in three main formats: zip-compressed raw cast files (.dat or .hex, .hdr, .con, .mrk, .bl Seasave data files); Seasave-processed .asc and .hdr (asciiout) down and up cast files; and combined data (1m depth binavg'd CTD .asc data merged with bottle data at ~20 depths) in csv-format. The combined-data csvs include columns of 'Seasave-processed-only' 1m data and 'bottle vs CTD regression-corrected' 1m data. Latest asc-hdr data: 0903JD (Mar 2009 CalCOFI); latest bottle-corrected, combined data: 0801JD.
- CTD Data in all formats via ftp: raw CTD data since 1992; asc CTD data since 2000; csv CTD+bottle data since 2006
Since 9308 (August 1993), the CalCOFI group has collected water samples and data using a Seabird CTD 24 bottle rosette. From Aug 1993 to mid 1998, a Seabird 9/11 rosette collected electronic and discrete samples from the standard 66 stations. In May 1998, the Seabird 9/11 CTD was upgraded to a 9/11plus, our current system (2004).
Typical sensors:
- Dual Temperature SBE 3 (pre 1998) or SBE 3plus & Conductivity SBE 4
- Oxygen - SBE 13 (Beckman) & SBE 43 (since 2003)
- Fluorometer
- SeaTech Fluorometer - 1993-2000
- Seapoint Fluorometer - since 2000
- Backups - WetLabs; Chelsea; Turner Design SCUFA
- Transmissometer (660nm)
- SeaTech 25cm Transmissometer or
- SeaTech 20cm Transmissometer or
- WetLabs 25cm Transmissometer
- PAR - Biospherical QSP-200L Scalar Irradiance Remote Sensor
- Pylon-Carousel - General Oceanics Pylon; Seabird SBE 32 Carousel (since ‘98)
- 24 - 10 liter (productivity-clean; no metals) PVC bottles
The dual-pumped CTD system records raw data at 24Hz (24 records/sec). Connected to a ship-board data-acquisition computer through an electronic winch wire, the CTD sensor data are displayed real-time on the computer screen. The CTD-rosette is lowered to the desired terminal depth (usually 515m; 30m/min to 100m then 60m/min to depth; bottom depth & weather-permitting) without stopping. The upcast bottle closure depths are based on the depth of the chlorophyll maximum observed during the downcast.
Water samples are taken from the rosette bottles: oxygens first, followed by salinity, nutrient, chlorophyll, and HPLC samples. Oxygen, salinity, nutrient, and chlorophyll samples are analyzed on the ship usually within 24 hours by the CalCOFI scientists, technicians, and volunteers.
CTD data are processed using the standard Seabird data processing methods-software. One decibar bin-averaged processed continuous data are then plotted against the discrete salinity, oxygen, and chlorophyll samples. The bottle-CTD salinity average offset is calculated; a CTD vs bottle oxygen 2nd order polynomial regression correction derived; 2nd or 3rd order polynomial fluorometer voltage vs extracted chlorophyll regression derived. These corrections are applied to the averaged continuous data, re-plotted then checked for correctness.
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