The Evaluation of Salinity Measurements from PALACE Floats

Abstract

Seven PALACE (Profiling Autonomous Lagrangian Circulation Explorer) floats were deployed in October 1996 in the Irminger Basin of the Atlantic Ocean as a U.K. contribution to the World Ocean Circulation Experiment. Of these floats, four were fitted with a conductivity?temperature?depth package. The floats were ballasted to drift at a depth of about 1500 m, above the Labrador Sea Water (LSW) cold and fresh extreme, and programmed to surface every 14 days. The floats made a profile during each ascent to the surface. The authors present a method to evaluate the performance of the conductivity sensors and to calibrate the float salinity data. Since the LSW appears to be relatively stable over a timescale of ?1?2 months and a length scale of ?50?100 km, the authors were able to make direct comparisons between the first year of float data and accurate ship-based measurements and, therefore, were able to correct for errors of the conductivity sensors. A correction was applied in all cases. The conductivity sensors were all stable within, or very close to, the manufacturer's specification, with a maximum drift for salinity of (0.0009 ± 0.0004) month?1.