5
Correcting for Temperature Drift Based on Pre- and Post-Cruise Laboratory Calibrations
Suppose a temperature sensor is calibrated (pre-cruise), then immediately used at-sea, and then returned for post-
cruise calibration. The pre-and post-cruise calibration data can be used to generate an offset correction for data
obtained between the pre- and post-cruise calibrations.
Calibration coefficients are calculated with the post-cruise calibration. Using the pre-cruise bath data and the post-cruise
calibration coefficients, a mean residual over the calibration temperature range is calculated.
residual = instrument temperature – bath temperature
Sea-Bird calculates and prints the value for the residual on the temperature calibration sheet (see
Appendix II: Example
Temperature Calibration Sheet
).
To correct temperature data taken between pre- and post-cruise calibrations:
Offset = b * (residual / n)
where
b = number of days between pre-cruise calibration and the cast to be corrected
n = number of days between pre- and post-cruise calibrations
residual = residual from calibration sheet as described above (see
Appendix II:
Example Temperature
Calibration Sheet
)
In the configuration (.con or .xmlcon) file, use the
pre-cruise calibration coefficients
and use the calculated
offset
for
the value of offset.
Note:
In our SEASOFT V2 suite of programs, edit the CTD configuration (.con or .xmlcon) file using the Configure
Inputs menu in Seasave V7 (real-time data acquisition software) or the Configure menu in SBE Data Processing (data
processing software).
Example
Instrument was calibrated (pre-cruise), used at sea for 4 months, and returned for post-cruise calibration.
Using
pre-cruise bath data
and
post-cruise coefficients
, the calibration sheet shows a mean residual of
-0.2 millidegrees C (-0.0002 °C).
For preliminary work at sea, use the
pre-cruise calibration coefficients
and
slope = 1.0, offset = 0.0
.
After the cruise, correct temperature data obtained during the cruise for drift using properly scaled values of
correction coefficients:
For data from the end of the first month (30 days) at sea:
Offset = b * (residual / n) = 30 * (-0.0002 / 120) = - 0.00005
;
Convert data using
pre-cruise coefficients
and
-0.00005
as the offset in the configuration file.
For data from the end of the second month (60 days) at sea:
Offset = b * (residual / n) = 60 * (-0.0002 / 120) = - 0.0001
;
Convert data using
pre-cruise coefficients
and
-0.0001
as the offset in the configuration file.
For data from the end of the third month (90 days) at sea:
Offset = b * (residual / n) = 90 * (-0.0002 / 120) = - 0.00015
;
Convert data using
pre-cruise coefficients
and
-0.00015
as the offset in the configuration file.
For data from the end of the 4-month cruise:
Offset = - 0.0002
;
Convert data using
pre-cruise coefficients
and
-0.0002
as the offset in the configuration file, or using
post-
cruise
coefficients and
0
as the offset in the configuration file.
114
Содержание SBE 45 MicroTSG
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