PEOCESSmG OCEANOGRAPHIC DATA 



PHOTOGRAPHIC 

 ENLARGER 



BACK OF BT PRINT 



Figure 1. — Processing of bathythermograph data: A, BT 

 slide; B, BT grid; C, arrangement of slide and grid in 

 photographic enlarger; D, bathythermogram print; and 

 E, supplementary data on back of print. 



trace crosses zero depth on the grid — is first 

 read and recorded for comparison with the sur- 

 face temperature as obtamed separately by 

 bucket thermometer which is listed on the log 

 sheet. Temperatiu-e is also read at the 50-foot 

 level, or at any selected level where the trace is 

 clear and nearly isothermal, for use in correcting 

 and setting up the slide for printing. Depth 

 difference between the top of the trace and zero 

 depth on the grid is then read and recorded for 

 use in determining the instrumental depth cor- 

 rection. The depth correction is taken as posi- 

 tive when the trace extends above the svirface 

 line on the grid; negative when it terminates 

 below the sm'face line. 



After all readings have been recorded, the 

 differences between the two surface tempera- 

 tiu-es (bucket minus BT) are entered for each 



TEMP. 

 CORRECTION 



DEPTH 

 CORRECTION 



Figure 2. — Form for calculating temperature and depth 

 corrections in processing bathythermograph data. 



slide, and the average difference is found for all 

 of the slides in the series. This is the instru- 

 mental temperature correction. This correction 

 is then applied to each reading at the 50-foot 

 level to give the set-up temperature for each 

 slide. Finally, the depth differences in the last 

 column are averaged to give the instrumental 

 depth correction. 



These corrections are applied in the process 

 of printing, and are thus incorporated in the 

 print. The slide and grid are placed in an 

 adjustable holder in a photographic enlarger. 

 The grid is moved horizontally relative to the 

 slide until the trace crosses the 50-foot level at 

 the corrected "set-up temperature"; it is then 

 moved vertically the amount of the average 

 depth correction. This double adjustment cor- 

 rects the entire trace for calibration errors in 

 the instrument (fig. IC). With the combined 

 slide and grid used as a negative, prints are made 

 on 3 by 5-inch, double weight, low contrast 

 paper (fig. ID). Three prints are usually made. 



When dry, the prints are checked for accur- 

 acy of applied correction in printmg. The 

 backs of the prints are then stamped with a 

 data stamp, and supplementary data are 

 transcribed from the log sheet. Standard 

 abbreviations and codes are used in the entries, 

 and necessary filing keys are given. 



In the example of figure lE, the number in 

 the upper left corner is the cruise file number, 

 "V" indicating that the observation was made 

 from a vessel, "215" denoting that this was 

 the two hundred and fifteenth vessel to submit 

 data, and "l" showing that it was the first set 

 of data to be received from that ship. The 

 number "lO" on the same line is the number 

 of the slide. 



