9.3.3. Correcting the Bathythermograms by the Permanent Thermocline 



Where variations in the ocean are expected to be considerable, curve fitting 

 techniques cannot be employed. However, there is indication that the bottom-most 

 portion of the Bathythermograph will remain fairly stable even in conditions of high 

 variability in the upper level. This bottom portion of the curve will be stable if it 

 reaches the top of the permanent thermocline. This occurs only with 900 foot Bathy- 

 thermographs. 



It has been shown that the top of the permanent thermocline is fairly stable 

 all year round, having variations not greater than present limitations of correcting 

 Bathythermograph data. Where the top of the thermocline is reached by the bottom- 

 most part of the trace, the trace can be superimposed. One is not depending upon an 

 independent temperature measurement at this point, but depending upon the fact 

 that this point does not vary in time, at least to any significant extent. This is a much 

 better point to correct the Bathythermograph than the surface, which does vary 

 considerably. 



The additional information which is received and the ability to reach into a 

 fairly stable portion of the ocean warrants the use exclusively of the 900 foot Bathy- 

 thermographs. The present state of development of the 900 foot Bathythermograph 

 is such that large failures in the bellows exist at this time. However, it is felt that 

 emphasis should be placed upon extended use of the 900 foot Bathythermograph. 



9.3.4. Use of Minimum Thermometer to Correct Bathythermographs 



In cases where the bottom of the trace does not reach the top of the permanent 

 thermocline and the variability of this part of the ocean is high, an independent 

 temperature measurement would have to be made at the bottom of the trace. This 

 is still an advantageous position to take an individual temperature measurement as 

 opposed to the surface ; because whatever the variability at this point, it is less than 

 the top. 



This suggests in lieu of the bucket or injection thermometer the use of an instru- 

 ment which would measure the temperature at the maximum depth to which the 

 Bathythermograph went. Such a minimum registering thermometer will have to 

 have a good response characteristic and would have to be designed to indicate the 

 temperature at that point, when brought out at the surface. The depth value would 

 not have to be recorded since it would be fixed to the Bathythermograph. 



While not much consideration has been given to the practicality of such an in- 

 strument, nevertherless in theory it would be highly advantageous over the pres- 

 ent techniques of correcting Bathythermographs at the surface. 



9.4. Establishment of Average Bathythermograms 



In many studies it is desirable to establish a typical average Bathythermograph 

 profile which is representative of the conditions over which the average was taken. 

 The recording of temperatures at given specific depths from which an average tem- 

 perature at each depth is then taken and from which an average Bathythermograph 

 is drawn often leads to erroneous results. This is especially true where internal 

 waves exist or where large variations in Bathythermograph sets exist. Such an av- 

 erage will round off any sharp corners in the Bathythermograph profile and distort 

 the actual gradients which exist. This technique must be foregone in lieu of the more 

 accurate curve fitting techniques as described above. 



Proper curve fitting techniques can be used not only to determine the variations 

 of the ocean, but also to obtain a typical average Bathythermograph. This type of 



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