ITS-90 TEMPERATURE SCALE
APPLICATION NOTE NO. 42
Revised - November 1996

Beginning January 1995, Sea-Bird temperature calibration certificates list a new set of coefficients labelled g, h, i, j, and F0. These coefficients correspond to ITS90 (T90) temperatures and should be entered by those researchers working with SEASOFT Versions 4.208 and higher. For the convenience of users who prefer to use older SEASOFT versions, the new certificates also list a, b, c, d, and F0 coefficients corresponding to IPTS68 (T68) temperatures as required by SEASOFT 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 4.200 and all subsequent SEASOFT versions convert between T68 and T90 according to the linear relationship:

T68 = 1.00024 * T 90

The use of T68 for salinity and other seawater calculations is automatic in all SEASOFT programs. However, when selecting temperature as a display variable, you will be promped to specify which standard (T90 or T68) is to be used to compute temperature. SEASAVE or other programs will recognize whether you have entered T90 or T68 coefficients in SEACON, and will either compute T90 temperature directly or calculate it from the Saunders linear approximation, depending on which coefficients were used and which display variable type is selected. For example, if you wish to display temperature according to the T68 standard, and g, h, i, j, F0 coefficients (T90) are entered in SEACON, select the temperature variable type as T68 and SEASAVE, DATCNV, or other modules will compute T90 temperature directly and multiply by 1.00024 to display T68. Conversley, if a, b, c, d, and F0 coefficients (T68) are entered in SEACON and the temperature variable type is selected as T90, SEASAVE, DATCNV, or other modules will compute T68 directly and divide by 1.00024 to display T90.

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.

SEA-BIRD ELECTRONICS, INC.
1808 - 136th Place Northeast, Bellevue, Washington, 98005 USA
Phone: (425) 643-9866 Fax: (425) 643-9954 e-mail: seabird@seabird.com

Copyright © SEA-BIRD ELECTRONICS, INC. Reprinted with permission.
Original version

Last modified: March 6, 1998