Sea-Bird Electronics SBE 38 Manual de usuario descargar pdf (Pagina 85)

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.

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Sea-Bird Electronics SBE 38 Manual de usuario Pagina 85