Thermal Lag Correction on Slocum CTD Glider Data

Garau, Bartolomé; Ruiz, Simón; Zhang, Weifeng G.; Pascual, Ananda; Heslop, Emma; Kerfoot, John; Tintoré, Joaquı́n

doi:10.1175/jtech-d-10-05030.1

Cited by 162 publications

(143 citation statements)

References 7 publications

(12 reference statements)

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“…The derivation of the salinities generally followed the procedure described by Garau et al (2011). They showed that applying a glider-speed-dependent delay to the temperature allowed for the calculation of optimal, i.e.…”

Section: Glider Surveymentioning

confidence: 99%

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

et al. 2014

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Abstract. Two consecutive summer upwelling events, each lasting for less than 24 h, were surveyed in high temporal and vertical resolution close to the Boknis Eck time-series station (BE) in the western Belt Sea (Baltic Sea) in summer 2010 with an autonomous glider. Driven only by moderate offshore winds both events resulted in more than 5 K cooling of surface waters, while only for the second event were significant irreversible changes in the vertical stratification observed. Generalizing the glider survey observations with hourly wind data from nearby meteorological stations, it is found that upwelling in the BE area occurs for wind directions between 190 to 260 • and wind speed exceeding 4 m s −1 . Based on these thresholds the wind-induced summer (June to September) upwelling conditions in the BE area for the period 1982 to 2012 are reconstructed. On average about 18 days of upwelling favourable wind conditions are found for the four summer months, with significant interannual variability ranging from 7.7 days (2006) to more than 28 days (1985). By aligning upwelling favourable wind conditions with the monthly BE surveys it is found that extreme anomalies in BE surveys follow extended periods of upwelling favourable winds.

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Section: Glider Surveymentioning

confidence: 99%

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

et al. 2014

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“…In this paper, we describe the processing procedures that we have developed for improving the accuracy of salinity derived from the UCTD. The results are also likely to be useful for other applications in which unpumped CTD measurements are made, for example, autonomous gliders (Garau et al 2011) or the Moving Vessel Profiler (Furlong et al 2000).…”

Section: Introductionmentioning

confidence: 97%

Processing of Underway CTD Data

Ullman

Hebert

2014

Journal of Atmospheric and Oceanic Technology

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A processing methodology for computation of accurate salinity from measurements with an underway CTD (UCTD) is presented. The UCTD is a rapidly profiling sensor package lacking a pump that relies on instrument motion to produce flow through the conductivity cell. With variable instrument descent rate, the flow through the cell is not constant, and this has important implications for the processing. As expected, the misalignment of the raw temperature and conductivity is found to be a function of the instrument descent rate. Application of a constant temporal advance of conductivity or temperature as is done with pumped CTDs is shown to produce unacceptable salinity spiking. With the descent rate of the UCTD reaching upwards of 4 dbar s 21 , the effect of viscous heating of the thermistor is shown to produce a significant salinity error of up to 0.005 psu, and a correction based on previous laboratory work is applied. Correction of the error due to the thermal mass of the conductivity cell is achieved using a previously developed methodology with the correction parameters varying with instrument descent rate. Comparison of salinity from the UCTD with that from a standard shipboard, pumped CTD in side-by-side deployments indicates that the processed UCTD salinity is accurate to better than 0.01 psu.

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“…Glider variables have been processed using an opensource MATLAB-based toolbox (https://bitbucket.org/ bastienqueste/uea-seaglider-toolbox/) in order to correct for differing timestamp allocations, sensor lags (Garau et al, 2011;Bittig et al, 2014), and to tune the hydrodynamical flight model (Frajka-Williams et al, 2011). Outliers outside of a specified range (e.g.…”

Section: Glider Sensorsmentioning

confidence: 99%

Measuring pH variability using an experimental sensor on an underwater glider

et al. 2017

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Abstract. Autonomous underwater gliders offer the capability of measuring oceanic parameters continuously at high resolution in both vertical and horizontal planes, with timescales that can extend to many months. An experimental ionsensitive field-effect transistor (ISFET) sensor measuring pH on the total scale was attached to a glider during the REP14-MED experiment in June 2014 in the Sardinian Sea in the northwestern Mediterranean. During the deployment, pH was sampled at depths of up to 1000 m along an 80 km transect over a period of 12 days. Water samples were collected from a nearby ship and analysed for dissolved inorganic carbon concentration and total alkalinity to derive the pH for validating the ISFET sensor measurements. The vertical resolution of the pH sensor was good (1 to 2 m), but stability was poor and the sensor drifted in a non-monotonous fashion. In order to remove the sensor drift, a depth-constant time-varying offset was applied throughout the water column for each dive, reducing the spread of the data by approximately two-thirds. Furthermore, the ISFET sensor required temperature-and pressure-based corrections, which were achieved using linear regression. Correcting for this decreased the apparent sensor pH variability by a further 13 to 31 %. Sunlight caused an apparent sensor pH decrease of up to 0.1 in surface waters around local noon, highlighting the importance of shielding the sensor from light in future deployments. The corrected pH from the ISFET sensor is presented along with potential temperature, salinity, potential density anomalies (σ θ ), and dissolved oxygen concentrations (c(O 2 )) measured by the glider, providing insights into the physical and biogeochemical variability in the Sardinian Sea. The pH maxima were identified close to the depth of the summer chlorophyll maximum, where high c(O 2 ) values were also found. Longitudinal pH variations at depth (σ θ > 28.8 kg m −3 ) highlighted the variability of water masses in the Sardinian Sea. Higher pH was observed where salinity was > 38.65, and lower pH was found where salinity ranged between 38.3 and 38.65. The higher pH was associated with saltier Levantine Intermediate Water, and it is possible that the lower pH was related to the remineralisation of organic matter. Furthermore, shoaling isopycnals closer to shore coinciding with low pH and c(O 2 ), high salinity, alkalinity, dissolved inorganic carbon concentrations, and chlorophyll fluorescence waters may be indicative of upwelling.

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Thermal Lag Correction on Slocum CTD Glider Data

Cited by 162 publications

References 7 publications

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

Processing of Underway CTD Data

Measuring pH variability using an experimental sensor on an underwater glider

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