SO_DYFAMED Time Series  - 1991-> ...

JC. MARTY : head of mission  and project leader

   HYDROLOGY  : J. CHIAVERINI

CTD Methodology

  Le matériel utilisé consiste en un ensemble « carrousel » (SBE32, Sea-Bird Electronics) et sonde (SBE9plus, Sea-Bird Electronics), reliés par un câble électroporteur à une unité de pont (SBE 11 Carousel Deck Unit, Sea-Bird Electronics). Le « carrousel » est constitué d'un support contenant 12 bouteilles de prélèvement (type Niskin) de 12 litres chacune 
Le premier profil hydrologique est réalisé jusqu’à 2 000 m (le fond est à 2 300 m). La collecte des échantillons est effectuée à la remontée à dix profondeurs de 2000 à 300 m.
Le deuxième profil concerne la couche 0-200 m, douze profondeurs sont échantillonnées de 200 à 5 m.
Les fichiers de données brutes obtenues par la bathysonde sont traités de retour au laboratoire avec l’aide du logiciel seasoft (Sea-Bird Electronics) selon le processus standard préconisé. Les capteurs température et conductivité sont étalonnés annuellement. Les données d’oxygène dissous sont fournies seulement à titre indicatif, elles ne peuvent être utilisées telles quelles. Les utilisateurs doivent les retraiter à partir des données brutes (disponibles à la demande) et des valeurs discrètes provenant des analyses par la méthode de Winkler (page biogéochimie dans ce site). 

Two CTD casts were obtained from each cruise, one for the 0–200 m layer, and the other for the 0–2000 m layer. From 1991 to 1993, the CTD system was a Sea-Bird SBE 9 underwater unit. Water for pigment (and other parameters) analyses was obtained using Niskin bottles from two hydrocasts performed between the two CTD casts. Since 1993 the CTD system consisted of a Sea-Bird SBE 911 Plus equipped with additional sensors (dissolved O₂ and fluorometer) mounted on a Sea-Bird rosette (SBE32 Carousel) equipped with twelve 12-l Niskin bottles.

 Sensors:

• -      Pressure: Digiquartz with temperature compensation

• -         Temperature : SBE 3-02/F

• -         Conductivity: (flow through cell): SBE 4-02/0

• -         Pump: SBE 5T

• -         Dissolved O2: (flow through cell) : SBE 13-02 (Beckman polarographic type) until 2002

• -         Dissolved O2   : SBE 43  (since 2003)

• -         Fluorescence: Aquatracka MKIII Chelsea fluorometer

Calibration: (routine procedure since 1999).

The temperature transducer and conductivity cell are returned to Sea-Bird each year for routine calibration. The membrane of the dissolved oxygen sensor was changed each year (SBE 13-02).

Data collection

The data acquisition is at 24 Hz frequency. The Sea-Bird deck unit averages these data to 1 Hz subsequently stored on the PC. Four files are saved for each cast:

• Daammjjx.hdr              Header file, lat., long., time, …

• Daammjjx.dat              Raw data file, binary

• Daammjjx.con            Configuration file (all the calibrations for the cast)

• Daammjjx.bl                Bottle file (record of parameters when each bottle is fired)

With            

• D for Dyfamed

• aa  for the Year

• mm for the Month

• jj for the Day

• x indicate the down cast (D, E, F..) or up cast (R,S,T)

Data Processing

Data processing is done back to the laboratory using the Sea-Bird software.

Cast processing :

DATCNV : Converts raw data from input .DAT to engineering units and stores the converted data  in .CNV files

ROSSUM (only for the up cast processing): Reads in the .ROS file and writes out a summary of the bottle data to a file (.BTL extension), and the bottle position data (.BL extension).

ALIGNCTD : Aligns temperature, conductivity and oxygen measurements in time relative to pressure.

 LOOPEDIT : Apply a pressure filter which eliminates all scans for which the CTD speed is less than 0.25 ms^-1.

DERIVE : Compute density, depth, potential temperature, salinity, oxygen from pressure, temperature and conductivity in the converted data files (.CNV extension).

BINAVG : Averages data in converted data (.CNV extension) files to 2 m resolution (5m for 1991-1993).

STRIP : Output selected columns of data from the input converted data files.

 ASCIIOUT : Output the header portion to a file (.HDR extension) and the data portion in ASCII engineering units to a file ( .ASC extension).

Finally the files produced are as follow:

Daammjjx.hdr              Header file, lat., long., time, meteorological observations…

Daammjjx.asc (or .xls) :            Data file which  report the following  :

pr: pressure [db]

t090: temperature, ITS-90 [deg C]

flC: fluorometer, chelsea

depS: depth, salt water [m]

potemp090: potential temperature, ITS-90 [deg C]

sal00: salinity, PSS-78 [PSU]

oxML/L: oxygen [ml/l]

oxPS: oxygen, percent saturation

sigma-é00: density, sigma-theta [kg/m^3]

oxsatML/L: oxygen saturation [ml/l]

References:

Sea-Bird Electronics, Inc. CTD Data acquisition software manual.

FIGURES