Summary: | Maintenance and Update Frequency: asNeeded Statement: The CTD-Satellite Relay Data Loggers (CTD-SRDLs) are built by the Sea Mammal Research Unit (SMRU, University of St. Andrews, UK), incorporating CTD sensors developed by Valeport Ltd (Devon, UK). The sensor head consists of a pressure transducer, a platinum resistance thermometer, and an inductive cell for measuring conductivity. The temperature and conductivity sensors have a precision (repeatability) of 0.005oC and 0.005 mS/cm, respectively. Before being taken into the field, devices are calibrated in the laboratory by Valeport. Some of the CTD-SRDLs (about half) were also tested at sea against a ship-based CTD before the deployment. CTD-SRDLs record hydrographic profiles during the ascent of seals, retaining only the deepest dive in each six-hour time interval, and transmitting profiles in a compressed form (between 10 and 25 data points per profile, depending on the tag program) through the Advanced Research and Global Observation Satellite (ARGOS) system. The accuracy of ARGOS geo-positioning is typically better than +/-5 km, because seals never stay at the surface more than a few minutes. New methods are currently under development by the ARGOS team, which should substantially improve the quality of positioning. Hydrographic profiles are post-processed using a unified procedure of editing, adjustment, and validation (Roquet, F. et al. Delayed-mode calibration of hydrographic data obtained from animal-borne satellite relay data loggers. J. Atmos. Ocean. Technol. 41, 787-801 (2011)). Each individual CTD-SRDL dataset is post-processed separately, as each tag has different technical specifications and a different life history. A standard set of tests, adapted from Argo standard quality-control procedures (Wong, A. et al. Argo Quality Control Manual v2.9. Argo Data Management, 54pp, http://www.argodatamgt.org (2013)), is first run to remove bad profiles, spikes, and outliers. For CTD-SRDLs with profiles in frozen areas, a temperature offset was estimated ...
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