6 



PROCESSING OCEANOGRAPHIC DATA 



and may be designed to read directly the total 

 correction, AT=C-\-I. 



A good method for constructing grapiis for 

 reversing thermometer corrections has been 

 outlined by Theisen (1947) (6). It consists of 

 preparing a large master graph of a series of 

 curves of t, using T'4-Vo as the abscissa and O 

 as the ordinate. Sections of this graph for the 

 required Vo may be reproduced photographic- 

 ally. By substituting the appropriate T' for 

 7"+Vo (i. e., by subtracting F„ from the 

 abscissa scale) correction graphs for individual 

 thermometers (such as shown in fig. 4) may be 

 prepared. 



The master graph may be constructed by sub- 

 stituting directly in one of the formulae for 





Figure 4. — Portion of individual protected thermometer 

 correction graph giving C and / for values of T' and t. 



values of t and T'-{-V„, or by plotting light con- 

 struction hues of T'—t and T' + V^. Perma- 

 nent lines of t can then be drawn through the 

 intersections of T'—t and T'-\-Vo and all scales, 

 (C, T' , and t), appropriately labeled. Shading 

 or coloring the strips makes reading easier. 



For use, only that portion of the master graph 

 is utilized that corresponds to the proper V o 

 (e. g., 102) for an individual thermometer. On 

 each individual correction graph an inde.x cor- 

 rection curve is added corresponding to T' and 

 C, as shown in figure 4. 



In this form only the observed values of T' 

 and t are necessary to obtain C and /. In the 

 example T'=5.06° C. and <=15.7° C, which 



from the graph gives C=— 0.20° C. and /= 

 — 0.01°C. By means of a pair of dividers the 

 sum C+Z may be scaled off in one operation. 

 The graph recommended for the correction 

 of individual protected reversing thermometers 

 (Sverdrup et al., 1944) (7) is shown in figure 5. 

 It, like the previous graph, requires only the 

 observed values T' and t to obtain the correc- 

 tions. To facilitate the construction of this 

 type of graph, table II, page 34, has been 

 compiled, which gives 7" — i for values of T'-\-Vo 

 and C (Soule, 1933) {S). 



Figure 5. — Portion of individual protected thermometer 

 correction graph giving AT for values of T' and t. 



In constructing individual correction graphs 

 the proper Va must be subtracted from y„-f T' , 

 and T' subtracted from T'—t of table II, so 

 that the coordinates will be T' and t, respec- 

 tively. Before the temperature con-ection lines 

 are finally drawn they are adjusted vertically 

 by the amount I along the calibration points 

 of T'. 



In this form the total AT for individual 

 thermometers may be obtained in one step. 

 The same example, where yo=102° C, 

 r = 5.06° C, and <=15.7° C, giving AT 

 equal to —0.21° C, is shown in figure 5. 



Similar tables and graphs may be prepared 

 to correct unprotected thermometer readings. 

 Table III, page 36, gives the expansion cor- 

 rection, C, for values of T^ + Vo fi'om 70° 

 to 200° C. and T„-<„ from 0° to 25° C. A 



