 Two types of METOCEAN Data Systems' drifters were deployed in the Southern Ocean: physical drifters and optical drifters. Physical drifters The physical drifters used were WOCE SVP GPS drifters, which measure location and sea surface temperature. The basic drifter design is shown in the schematic to the right. GPS location data are acquired once per hour. Sea surface temperature measurements are made just before and after each GPS fix, and averaged. These hourly data are then transmitted to ARGOS every 400 s. ARGOS positioning occurs if 5 or more GPS fix attempts have failed. The typical lifetime of these drifters in the Southern Ocean is 4.5 months. Optical drifters The optical drifters used were WOCE/OCM/GPS (Ocean Color Monitor) Lagrangian drifters. The basic drifter design is similar to that of the physical drifters (schematic to the right), except that optical sensors are included in the surface unit (diagram below) and the drogue dimensions are different (40 cm diameter, 12.27 m long) to decrease its influence on the optical measurements.
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| These drifters contain sensors that measure the water temperature and optical sensors from Satlantic, Inc., that measure downwelling irradiance above the sea surface and upwelling radiance just below the sea surface . The irradiance is measured at a center wavelength of 490 nm and the radiances are measured at seven wavebands centered at: 412, 443, 490, 510, 555, 670, and 683 nm. The 683 nm sensor has a bandpass of approximately 10 nm. The remaining sensors have a bandpass of 20 nm. These optical sensors were calibrated by Satlantic, Inc., before deployment. Optical measurements were made every 100 s and averaged over a one hour period. Sea surface temperature measurements were made alternately with GPS location fixes each hour, hence SST and GPS location data are not available at the same time. Each set of hourly data was transmitted to ARGOS every 400 s. The typical lifetime of these drifters in the Southern Ocean is 3 months.
Drifter diagrams adapted from
a drawing by David Reinert, Oregon State University. |
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