CHAPTER 4 



DRAWING OCEANOGRAPHIC GRAPHS AND PROFILES 



4-1 GENERAL REMARKS.— Graphs and 

 profiles of oceanographic data serve many uses 

 in studies and interpretations of these data. 

 Some of the immediate important shipboard 

 appUcations include checking for possible er- 

 rors in computations, chemical analyses, spacing 

 the Nansen bottles, and obtaining the standard 

 depth values from the plotted observed values. 



All graphs and profiles should be drawn with 

 great care. Use a pencil no softer than a 

 number 3 drawing pencil. Keep the point 

 sharp and draw fine clear lines. Plot all data 

 accu^atel5^ Use french and ship curves to 

 construct lines. Draw the curves through the 

 plotted points in such a manner that the points 

 appear to lie on the curve rather than being 

 connected by curved lines. This can be done 

 easily with a little practice. 



4-2 PLOTTING OBSERVED OCEANO- 

 GRAPHIC VALUES.— Observed values for 

 temperature, salinity, dissolved oxygen, and 

 density, as well as any other determined values, 

 are plotted against depth. For this purpose, 

 Navy survey ships use a special graph printed 

 by the Hydrographic Office and known as an 

 Oceanographic Station Plotting Sheet (H. O. 

 Misc. 15,252-1). A sample sheet is shown 

 in figure 4-1. If these sheets are not avail- 

 able aboard ship, any good quality graph paper 

 scaled 10 x 10 to the H inch may be used. 



4-3 Standard Symbols and Scales. — To aid 

 in interpretation of data and eliminate unneces- 

 sary replotting ashore, the Hydrographic Office 

 uses a standard set of symbols and scales for 

 temperature, salinity, oxygen, and density, as 

 shown below. These symbols and scales are 

 given on the Oceanographic Station Plotting 

 Sheet. The point in the symbol indicates the 

 value and the symbol indicates the type of 

 observation. 



40 



On the vertical scale, K inch equals 100 

 meters of depth. If the station depth exceeds 

 the length of the graph paper extend the graph 

 by attaching part of another sheet to the bottom 

 with rubber cement. 



4-4 OBTAINING INTERPOLATED VAL- 

 UES. — Temperature, salinity, oxygen, and 

 density values for standard depths are inter- 

 polated from the plotted observed value curves 

 and are recorded on oceanographic log sheet E. 

 To find an interpolated value, simply locate 

 the intersection of the curve and the horizontal 

 line which represents the desired standard depth 

 and read the corresponding value at the top of 

 the graph. The standard depths are printed 

 on the E-sheet. 



Interpolated standard depth values obtained 

 for temperature, salinity, and density may be 

 checked by entering a Nomograph for the 

 Determination of Density from Salinity and 

 Temperature of Sea Water (tables 1 to 6, 

 identified as H. O. Misc. 15530-1 to 6) with 

 the values for temperature and salinity. 

 The resulting density value must agree with 

 the interpolated value. In like manner, the 

 density values of the temperature-salinity 

 (T-S) curve can be checked. In the event the 

 values do not agree then at least one of observed 

 values is not valid and must be reviewed. 



4-5 TEMPERATURE-SALINITY (T-S) 

 CURVES. — To plot temperature-salinity rela- 

 tionships, referred to as T-S curves. Navy 

 survey ships use special graph paper printed 

 by the Hydrographic Office called a Tempera- 

 ture-Salinity Plot (H. O. Misc. 12,252-B). 

 A sample sheet is shown in figure 4-2. This 

 graph indicates density values for the range 

 of temperature and salinity it covers. If these 

 sheets are not available aboard ship, any good 

 quality graph paper scaled 10 x 10 to the }i inch 

 may be used. The same temperature and 

 salinity scales as given in section 4-3 are used. 

 Temperature is represented on the vertical 

 scale and salinity on the horizontal scale. 



Using the data for temperature and salinity 

 from the E-sheet, plot the observed T-S values 

 for each depth. Circle each point and draw a 

 smooth curve through the plotted points. Now 



H. O. 607 



