APPLICATION NOTE NO. 42
Application note in pdf format
Beginning January 1995, Sea-Bird temperature calibration certificates list a new set of coefficients labeled g, h, i, j, and F0. These coefficients correspond to ITS90 (T90) temperatures and should be entered by users working with SEASOFT-DOS Versions 4.208 and higher (and all versions of SEASOFT-Win32). For the convenience of users who prefer to use older SEASOFT versions, the certificates also list: a, b, c, d, and F0 coefficients corresponding to IPTS68 (T68) temperatures as required by SEASOFT-DOS versions older than 4.208.
It is important to note that the international oceanographic research community will continue to use T68 for computation of salinity and other seawater properties. Therefore, following the recommendations of Saunders (1990) and as supported by the Joint Panel on Oceanographic Tables and Standards (1991), SEASOFT-DOS 4.200 and later and all versions of SEASOFT-Win32 convert between T68 and T90 according to the linear relationship:
T68 = 1.00024 * T90
The use of T68 for salinity and other seawater calculations is automatic in all SEASOFT programs. However, when selecting temperature as a display/output variable, you will be prompted to specify which standard (T90 or T68) is to be used to compute temperature. SEASOFT recognizes whether you have entered T90 or T68 coefficients in the configuration (.con) file, and computes T90 temperature directly or calculates it from the Saunders linear approximation, depending on which coefficients were used and which variable type is selected.
For example, if g, h, i, j, F0 coefficients (T90) are entered in the .con file and you select the temperature variable type as T68, SEASOFT computes T90 temperature directly and multiplies by 1.00024 to display T68. Conversely, if a, b, c, d, and F0 coefficients (T68) are entered in the .con file and you select the temperature variable type as T90, SEASOFT computes T68 directly and divides by 1.00024 to display T90.
NOTE: The CTD configuration (.con) file is edited using the Configure menu (in SEASAVE or SBE Data Processing in our SEASOFT-Win32 suite of programs) or SEACON (in SEASOFT-DOS).
Also beginning January 1995, Sea-Bird's own temperature metrology laboratory (based upon water triple-point and gallium melt cell, SPRT, and ASL F18 Temperature Bridge) converted to T90. These T90 standards are now employed in calibrating all Sea-Bird temperature sensors, and as the reference temperature used in conductivity calibrations. Accordingly, all calibration certificates show T90 (g, h, i, j) coefficients that result directly from T90 standards, and T68 coefficients (a, b, c, d) computed using the Saunders linear approximation.
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