7
SBE 43 Calibration Adjustment or Data Correction for Long-Term Deployments
using Sparse Reference Values
The following methods are used to correct fouled SBE 43 sensor data collected primarily in moored applications.
They can be applied to oxygen data when only sparse reference samples are available to verify sensor calibration.
The methods should be applied only to individual sensors (i.e., a correction calculated for one sensor cannot be
applied to other sensors on the mooring). Once a sensor on a mooring is serviced (cleaned) or swapped out, the
process should be repeated. Specific applications for moored oxygen sensors include:
• Data correction when periodic reference check values are collected while the sensor continues sampling in situ
(but no sensor maintenance is conducted) - This data correction is particularly useful for assessing when sensors
need to be serviced for real-time data collection programs. It is also applicable for post-processing of data in
non-real-time applications. See Example of In Situ Data Correction for Continuous Real-Time Mooring Data
Applications below.
• Data correction when only pre- and post-deployment reference samples or factory calibrations are available –
This data correction requires that no sensor maintenance, such as cleaning, be performed between the pre-
and post-deployment reference samples or factory calibrations. See Example of Post-Processing Data
Collection below.
Basic Principal
The SBE 43 sensor output is linear with respect to oxygen concentration and maintains a relatively stable output at
zero oxygen. Electrochemical drift, a limitation in previous Clark designs, exists somewhere below the calibration
uncertainty of 1 µmol/kg and has not been observed in several years of factory calibration data nor in long-
deployments on Argo floats and moorings. Therefore, any sensor drift with time is attributed to fouling of the
membrane, either biological or waterborne contaminants (i.e., oil). The main term of interest for correcting fouling
drift is the SOC term in the SBE 43 sensor calibration equation, as shown here again in Equation 3:
+∗= )()/( VoffsetVSoclmlOxygen eqn 3
Where:
SOC is the linear slope scaling coefficient
V is the SBE 43 output voltage signal (volts)
V
offset
is a fixed sensor voltage at zero oxygen
φ (defined in Equation 2 earlier in this document) includes terms that correct for the effects of temperature and
pressure, and also includes oxygen solubility dependence on temperature and salinity. Because these terms remain
essentially constant with fouling and sensor age, we will not concern ourselves with φ for this application.
Furthermore, an insufficient number of water samples makes estimation of Voffset uncertain, therefore, we will
restrict the correction derived here to the SOC term, which is the calibration term affected most by the fouling.
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