scholarly journals A Correction for the Thermal Mass–Induced Errors of CTD Tags Mounted on Marine Mammals

2018 ◽  
Vol 35 (6) ◽  
pp. 1237-1252 ◽  
Author(s):  
Vigan Mensah ◽  
Fabien Roquet ◽  
Lia Siegelman-Charbit ◽  
Baptiste Picard ◽  
Etienne Pauthenet ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Southern Ocean ◽  
Marine Mammals ◽  
Thermal Mass ◽  
Density Estimates ◽  
Mass Error ◽  
Correction Scheme ◽  
Salinity Data ◽  
Temperature Depth

AbstractThe effect of thermal mass on the salinity estimate from conductivity–temperature–depth (CTD) tags sensor mounted on marine mammals is documented, and a correction scheme is proposed to mitigate its impact. The algorithm developed here allows for a direct correction of the salinity data, rather than a correction of the sample’s conductivity and temperature. The amplitude of the thermal mass–induced error on salinity and its correction are evaluated via comparison between data from CTD tags and from Sea-Bird Scientific CTD used as a reference. Thermal mass error on salinity appears to be generally O(10−2) g kg−1, it may reach O(10−1) g kg−1, and it tends to increase together with the magnitude of the cumulated temperature gradient (THP) within the water column. The correction we propose yields an error decrease of up to ~60% if correction coefficients specific to a certain tag or environment are calculated, and up to 50% if a default value for the coefficients is provided. The correction with the default coefficients was also evaluated using over 22 000 in situ dive data from five tags deployed in the Southern Ocean and is found to yield significant and systematic improvements on the salinity data, including for profiles whose THP was weak and the error small. The correction proposed here yields substantial improvements in the density estimates, although a thermal mass–induced error in temperature measurements exists for very large THP and has yet to be corrected.

Drift Characteristics of a Moored Conductivity–Temperature–Depth Sensor and Correction of Salinity Data

2005 ◽  
Vol 22 (3) ◽  
pp. 282-291 ◽  
Author(s):  
Kentaro Ando ◽  
Takeo Matsumoto ◽  
Tetsuya Nagahama ◽  
Iwao Ueki ◽  
Yasushi Takatsuki ◽  
...  
Keyword(s):  
Linear Trend ◽  
Drift Time ◽  
Calibration Data ◽  
Depth Sensor ◽  
Salinity Data ◽  
Corrected Data ◽  
Western Portion ◽  
Triton Buoy ◽  
Temperature Depth

Abstract The temperature and conductivity drift (time change of the characteristics) of moored SBE37IM conductivity and temperature (CT) sensors was investigated by pre- and postdeployment calibration of the Triangle TransOcean Buoy Network (TRITON). This buoy network comprises the western portion of the basinwide (Tropical Atmosphere Ocean) TAO/TRITON buoy array, which monitors phenomena such as El Niño and contributes to forecasting climate change. Over the time of deployment the drift of the temperature sensors was very small, within 3 mK of the postdeployment calibration data. The drift of the conductivity sensors was more significant. After 1 yr of mooring, conductivity drift observed in the shallowest layer (1.5–100 m) was positive and 0.010 S m−1 [equivalent to 0.065 (PSS-78) at 30°C and 6 S m−1; here, 1 S is 1 Ω−1] at 6 S m −1 on average. Drift observed in the thermocline layer (125–200 m) was also positive and 0.0053 S m−1 [0.034 (PSS-78)] at 6 S m−1 on average. Conversely, the drift of conductivity in the deepest layer (250–750 m) was 0.00002 S m−1 with a standard deviation of 0.001 S m−1 [0.0065 (PSS-78)]. Assuming a linear trend of conductivity drift with time, the authors attempted to correct the conductivity data using the postdeployment calibration data. The corrected data for about 80% of the sensors exhibited smaller differences than the uncorrected data when compared with the in situ conductivity–temperature–depth (CTD) data. However, the corrected salinity data became worse than the uncorrected data for about 20% of the sensors. The reasons for these errors are also discussed in this paper.

Correction for Systematic Errors in the Global Dataset of Temperature Profiles from Mechanical Bathythermographs

2020 ◽  
Vol 37 (5) ◽  
pp. 841-855 ◽  
Author(s):  
Viktor Gouretski ◽  
Lijing Cheng
Keyword(s):  
Reference Data ◽  
Heat Content ◽  
Systematic Errors ◽  
Global Ocean ◽  
Temperature Profiles ◽  
Empirical Correction ◽  
Correction Scheme ◽  
Temperature Depth

AbstractA homogeneous, consistent, high-quality in situ temperature dataset covering some decades in time is crucial for the detection of climate changes in the ocean. For the period from 1940 to the present, this study investigates the data quality of temperature profiles from mechanical bathythermographs (MBT) by comparing these data with reference data obtained from Nansen bottle casts and conductivity–temperature–depth (CTD) profilers. This comparison reveals significant systematic errors in MBT measurements. The MBT bias is as large as 0.2°C before 1980 on the global average and reduces to less than 0.1°C after 1980. A new empirical correction scheme for MBT data is derived, where the MBT correction is country, depth, and time dependent. Comparison of the new MBT correction scheme with three schemes proposed earlier in the literature suggests a better performance of the new schemes. The reduction of the biases increases the homogeneity of the global ocean database being mostly important for climate change–related studies, such as the improved estimation of the ocean heat content changes.

scholarly journals Sensor Corrections for Sea-Bird SBE-41CP and SBE-41 CTDs

2007 ◽  
Vol 24 (6) ◽  
pp. 1117-1130 ◽  
Author(s):  
Gregory C. Johnson ◽  
John M. Toole ◽  
Nordeen G. Larson
Keyword(s):  
Thermal Inertia ◽  
Sensor Response ◽  
The Arctic ◽  
Thermal Mass ◽  
Surface Layers ◽  
Mass Error ◽  
Oceanographic Data ◽  
Energy Profiling ◽  
Conductivity Cell ◽  
Temperature Depth

Sensor response corrections for two models of Sea-Bird Electronics, Inc., conductivity–temperature–depth (CTD) instruments (the SBE-41CP and SBE-41) designed for low-energy profiling applications were estimated and applied to oceanographic data. Three SBE-41CP CTDs mounted on prototype ice-tethered profilers deployed in the Arctic Ocean sampled diffusive thermohaline staircases and telemetered data to shore at their full 1-Hz resolution. Estimations of and corrections for finite thermistor time response, time shifts between when a parcel of water was sampled by the thermistor and when it was sampled by the conductivity cell, and the errors in salinity induced by the thermal inertia of the conductivity cell are developed with these data. In addition, thousands of profiles from Argo profiling floats equipped with SBE-41 CTDs were screened to select examples where thermally well-mixed surface layers overlaid strong thermoclines for which standard processing often yields spuriously fresh salinity estimates. Hundreds of profiles so identified are used to estimate and correct for the conductivity cell thermal mass error in SBE-41 CTDs.

In Situ Calibration of Moored CTDs Used for Monitoring Abyssal Water

2008 ◽  
Vol 25 (9) ◽  
pp. 1695-1702 ◽  
Author(s):  
Hiroshi Uchida ◽  
Takeshi Kawano ◽  
Masao Fukasawa
Keyword(s):  
Potential Temperature ◽  
Pressure Sensors ◽  
Heat Content ◽  
Deep Ocean ◽  
Volume Transport ◽  
In Situ Calibration ◽  
Before And After ◽  
Salinity Data ◽  
Temperature Depth

Abstract To monitor changes in heat content and geostrophic volume transport of abyssal water accurately, 50 moored conductivity–temperature–depth (CTD) recorders used for density measurements were calibrated in situ by simultaneous observations with accurate shipboard CTDs. Comparisons of the data from the moored and shipboard CTDs showed pressure sensitivities of 0–3 mK at 6000 dbar for the temperature sensors of the moored CTDs. From the in situ calibrations, the uncertainties of the moored CTD data for the deep ocean (≥3000 dbar) were estimated to be 0.6 dbar, 0.6 mK, and 0.0026 for pressure, temperature, and salinity, respectively, relative to the shipboard CTD reference. Time drifts of the moored CTD data, estimated from the in situ calibrations before and after 17- or 14-month mooring deployments in the deep ocean, were considerably smaller than typical stabilities as specified by the manufacturer. However, time drifts of the pressure sensors tended to be negative and the result suggests that pressure data from most present Argo floats, which use the same type of pressure sensor, may have a systematic negative bias. Time series salinity data calculated from the in situ–calibrated CTDs were slightly biased (mean of +0.0014) with respect to the shipboard CTD salinity data, based on potential temperature–salinity relationships, possibly due to a disequilibrium of the moored CTD conductivity sensors during the in situ calibrations.

scholarly journals A Modeling Case Study of Mixed-Phase Clouds over the Southern Ocean and Tasmania

2010 ◽  
Vol 138 (3) ◽  
pp. 839-862 ◽  
Author(s):  
Anthony E. Morrison ◽  
Steven T. Siems ◽  
Michael J. Manton ◽  
Alex Nazarov
Keyword(s):  
Southern Ocean ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Weather Research And Forecasting ◽  
Marine Stratocumulus ◽  
Cloud Structure ◽  
In Situ Observations ◽  
Cloud Tops ◽  
Mixed Phase Clouds

Abstract The cloud structure associated with two frontal passages over the Southern Ocean and Tasmania is investigated. The first event, during August 2006, is characterized by large quantities of supercooled liquid water and little ice. The second case, during October 2007, is more mixed phase. The Weather Research and Forecasting model (WRFV2.2.1) is evaluated using remote sensed and in situ observations within the post frontal air mass. The Thompson microphysics module is used to describe in-cloud processes, where ice is initiated using the Cooper parameterization at temperatures lower than −8°C or at ice supersaturations greater than 8%. The evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed-phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus-like clouds with maximum heights of between 3 and 5 km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than −10°C, WRF produces widespread supercooled cloud fields with little glaciation. This is consistent with the limited in situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The simulations are further explored to evaluate any orographic signature within the cloud structure over Tasmania. No consistent signature is found between the two cases.

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