Part I.— PROCESSING PROCEDURES 



INTRODUCTION 



Physical oceanographic measurements taken 

 at sea require careful examination, correction, 

 and conversion before they can be put in a form 

 suitable for analysis. Such processing: of ocean- 

 ographic data involves a considerable amount 

 of practical experience to judge the reliability 

 of the records from instruments which operate 

 blindly below the sea surface. Corrections for 

 instrumental errors and for errors inherent in 

 the methods of obtaining data are necessary 

 in order to determine the basic values of tem- 

 perature and salinity for different depths in the 

 sea. Conversion of sea observations to stand- 

 ard units is desirable for comparison with other 

 oceanographic data. Also, certain calculations 

 are required to derive dependent quantities, 

 such as specific volume, density, and currents. 



Processing of data is a time-consuming 

 operation, and many short cuts have been 

 devised.. The choice of method depends upon 

 the amount of data to be processed and upon 

 individual preference. For these reasons the 

 following section gives the fundamental for- 

 mulae and outlines a choice of procedures for 

 correcting and converting field data in order 

 to obtain the desired results. 



Although this section deals with processing 

 ashore, much of the processing could be accom- 

 plished aboard ship. Processing aboard ship 

 has the advantage that the results provide an 

 immediate guide for future observations. On 

 the other hand more space and more time are 

 usually available on shore, as well as more 

 stable conditions, resulting in more accurate 

 work. Regardless of where the work is carried 

 on, the following procedures, examples, and 

 tables should prove useful for the processing 

 of physical oceanographic data. 



D.I.— PROCESSING OF CONTINUOUS 

 TEMPERATURE AND SALINITY DATA 



BATHYTHERMOGHAMS 



Several instruments are in use which produce 

 a continuous record of temperature and sa- 

 linity with depth or time. The continuous 



recording instrument most widely used at 

 present is the bathythermograph, or "BT," 

 which records temperature against depth on a 

 smoked glass slide (Spilhaus, 1938) (/).* 



A standardized method has been developed 

 for processing bathythermograph slides to con- 

 vert the data into a form convenient for 

 analysis and filing. Briefly, a transparent 

 tompcrature-depth grid is superimposed on a 

 slide, the relative positioning of the slide and 

 grid is adjusted to correct for any instrumental 

 error, and the superimposed combination is 

 used as a negative in making photographic 

 prints. Pertinent meteorological and other 

 data are then entered on the back of each 

 print. 



As received for processing, the smoked slides 

 show the temperature-depth trace made by the 

 instrument, together with the following written 

 information: Slide number, time (G. c. t.), 

 date, and serial number of the BT instrument 

 (fig. lA). The trace and written data are 

 preserved bj' a coat of lacquer which has been 

 applied on shipboard. Accompanying each 

 set of slides is a log sheet listing the data given 

 on each slide, and in addition giving the posi- 

 tion of each observation, the temperature of 

 the sea surface as determined by bucket 

 thermometer, and the meteorological conditions 

 at the time of the observation. 



For each BT instrument there is an individual 

 grid (fig. IB) calibrated for use with slides from 

 that particular instrument. The grid consists 

 of lines for temperature and depth which have 

 been marked on a glass slide of the same size 

 as the bathy thermogram (1 by 1.75 inches). 



Upon receipt, the BT slides and log sheets are 

 recorded and checked for errors and discrep- 

 ancies in the data. Each slide is then placed 

 with the appropriate grid in a small magnifying 

 viewer in order to determine temperature and 

 depth corrections. A form similar to that shown 

 in figure 2 is used for tabulation and calculation. 



Surface temperature — that is, the tempera- 

 ture at top of trace or temperature at which the 



'Italic numbers In parentheses refer to References, p. 28. 



