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Surfact 3376 (blue) and 3377(red) - Triaxys mooring (42°29'310N 3°10'100E) / Banyuls sur Mer

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Surface Autonomous Conductivity and Temperature(SURFACT)

AntonioLourenço1, Jacqueline Boutin1, Jacqueline Etcheto1, Thierry Monglon1 and Jean Jacques Naudin2

(1) Laboratoire d'Océanographie Dynamique et de Climatologie (LODYC - CNRS), PARIS France, (2) Laboratoire Arago (CNRS), Banyuls sur Mer France,

SURFACT has recently been developped at LODYC to determine salinity at 30cm below the ocean surface with an accuracy of 0.1PSU. With an autonomy of one month it is well suited for a Sea Surface Salinity monitoring during airborne campaigns and could be used for future Cal/Val studies of SMOS and AQUARIUS radiometers.

The instrument are presented as well as in-situ tests conducted at sea.

2 SURFACT were attached to a surface buoy during one monthfrom february 26 to march 27 2004 near Laboratoire Arago,

Banyuls sur Mer (Mediterranean Sea) in a coastal region,0.5 miles from the coast.

Calibration tank from EPSHOM. Stability ~ 0.002°C

AccuracyTemperature ± 0.001°C

Conductivity ± 0.002mS/cm

Two SURFACT from february 26 to march 27 (blue and red lines).The blue one stopped after 16 days due to a transmiter failure.

The black squares in salinity plot are the reference salinity measured by an Autosal Guild Line Thermosalinimeter.

Samples taken on the first meter depth differ from SURFACT measurements

by 0.06 ±0.03PSU for the blue one andby 0.20 ±0.05PSU for the red one.

These results include differences due to variations in samples depth.The two SURFACT salinity differ by less than 0.05PSU at the

deployment and by 0.2PSU after 16 days. This small drift will be studied during the post calibration (in progress).

The two SURFACT temperature measurements agree within 0.01°C.

Conductivity sensor:Range: 0 ... 65 mS/cm Resolution: 1 µS/cm (16 bit)Accuracy: 50µS/cmLong term stability: depends on electrodes surface conditionsStability: 5µS/cmTime constant: 200 msecReady after power on: max 10 sec (typ. 5 sec)Measuring frequency: 500 HzDimensions of cell: 40mm * ø18mmMax depth: 500 mTypes: 7 titanium rings inside a quartz glass cylinder

Temperature sensorRange: -2°C ... 36°CResolution: 0,6 mKAccuracy of calibration: better than 10 mKLong term stability type 2 mK/yearTime constant of PT100: approx. 5 secTime constant of circuitry: 100 msecReady after power on: < 2 secMeasuring frequency: 500 HzReady after immersion: approx 5 min for 16 bit accuracyType: Pt 100 moulded in the Conductivity sensorCircuitry: linearized Wheatstone AC bridge

Zoom from march 4 to 8.Fast temperature and salinity variations due to coastal currents

SURFACT is an autonomous surface float ; it integrates a conductivity and temperature sensor

(from Sea and Sun Technologies, De) with an Argos transmeter (from SERPE IESM, Fr).

It has been designed to transmittemperature and conductivity in order to calculate SSS at better than 0.1PSU every 10 minutes during 30 days

at 30cm below sea surface.

SST

SSS

SST

SSS

Zoom from march 12 to 15.Rainfall events (3mm/h) on march 13 leads to SSS decrease of

0.1PSU.

SSS

rainfall

We acknowledge G. Reverdin for helpful discussions on SURFACT, the Néreïs crew from Laboratoire Arago, who

deploys and recovers the SURFACT andMarc Le Menn from l’ EPSHOM, who provides us facilities

for pre and post calibrations.This study has been performed under CNES / TOSCA

These results are very encouraging (precision <0.05PSU).Post calibration of these SURFACT are in progress.

Comparaison with meteorological data from february 25 to marchMeteorological data were taken at Cap Béar (Météo France, Fr

At less than 1 mile from SURFACT.We clearly see the effect of low wind speed on surface

temperature and salinity : - diurnal cycles from march 3 to 6 and march 15 to 21

- SST warming from march 16 to 21