1) All XBT sample depths are re-computed (if nesessary) according to the SIPPICAN FRE

2) XBT observed temperature is corrected for thermal bias according to the time (year) of the observation (see thermal_bias correction files)

thermal_bias_t4t6_vs_year.dat
thermal_bias_t7db_vs_year.dat

T-corrected = T-observed - Thermal_Bias

3) Depth correction factor ("stretching") is calculated using the following formula (as in Gouretski and Reseghetti, 2010, but with different numerical values of the coefficients).

nominal_stretching(Z) = b + a/Z - c*Z**2


For numerical values of a, b, and c see stretching parameter files.

stretch_approx_parameters_t4t6_vs_year.dat
stretch_approx_parameters_t7db_vs_year.dat

4) This "nominal" depth-depending stretching factor is further modified depending on the deviation of the XBT-profile mean temperature (tmean_profile) from the "nominal" mean temperature (tmean_nominal). (Values of tmean_nominal are given in mean_temperature files).

tmean_t4t6.dat
tmean_t7db.dat

Here mean temperature refers to the mean temperature within the respective layer between the ocean surface and the sample depth (Z) for which the correction is calculated.

delta = tmean_profile(Z) - tmean_nominal(Z)

final_stretching (Z) = nominal_stretching(Z) + delta*0.0015

5) "Observed" (Sippican) XBT sample depth is now finally corrected:

Z_corrected = Z*final_stretching(Z)

V. Gouretski, 31 May 2010, KlimaCampus, Hamburg