SURVEY OF OCEANOGRAPHIC INSTRUMENTATION 



MEASURE- CHARACTERISTICS 



MENT DEVICES AND 



FUNCTION LIMITATIONS 



COMMENTS 



Ocean 

 Temperature 



Mechanical (BT) 

 Bathythermograph 



Depth: to 900 feet/Accuracy: 



± 10 feet 

 Temperature: -2.2 to 32°C/ 



Accuracy: +0.rC 

 Poor accuracy 



Deep-Sea Reversing 

 Thermometer 



Depth: to 20,000 feet /Accura- 

 cy: + 100 feet 



Temperature: -2 to SCC/Ac- 

 curacy: +0.01°C 



Not continuous: too delicate 



Wire- Wound Depth: Surface 



Resistance Temperature: —5 to 30°C and 



Thermometer —25 to 5°C/Accuracy: 



+ 0.1°C 

 Poor accuracy except near sur- 

 face 



Thermocouple Depth: to 200 feet 



Temperature: -50 to 10°C/Acr 



curacy: ±0.5°C 

 Requires laborious calibration: 

 thermocouple reference junc- 

 tions must be kept at a con- 

 stant known temperature 



In temperature measurement work the Mechanical 

 Bathythermograph has long been the oceanogra- 

 pher's workhorse. The "BT," together with those 

 previously noted herein, and an airborne radiation 

 thermometer (for surface depths,- temperature 

 range — 2 to 35°C, accuracy ±0.2°C), comprise for 

 the most part present-day temperature instrumen- 

 tation. Various telemetering and self-containing 

 recording systems, infra red devices, temperature 

 probes.and electronic Bathythermographs (Hytech) 

 are also being used, developed, and evaluated. 

 Specifications for improved systems have been doc- 

 umented as those requiring repeatability and ac- 

 curacy + O.I°C (for buoyancy problems the accura- 

 cy may be approximately + .05°C), quick reaction 

 time sensors, durability, watertightness. linear out- 

 put and standardization of output signals com- 

 patible to computer and machine tabulation. 



Depth 



Edo 255 



(Depth of bottom) 



Accuracy: 0.1% of depth 

 Experiences numerous break- 

 downs 



Unprotected Probable error of depths: +15 



Mercury feet for depths less than 3,000 



Thermometer feet; at greater depths to 



about 0.5% 

 Too delicate; has limited appli- 

 cation: is not continuous 



Mechanical Pressure 

 Transducer (Bour- 

 don tube, bellows, 

 helical coil, aneroid, 

 etc.) 



Depth: to 1,500 feet/Accura- 

 cy: + 15 feet 

 Erratic 



Electronic Pressure 

 Transducer ("Vibra- 

 tion," strain gauge, 

 variable reluctance 

 gauge, etc.) 



Depth: to 1,500 feet/Accura- 

 cy :+ 4 feet (Accuracy of the 

 transducer is generally limited 

 by the recording apparatus) 



Erratic; transducer accuracy is 

 limitation 



Depth is most difficult to measure accurately. New 

 depth measuring devices, for example, require pres- 

 sure transducers which are expendable, adaptable 

 for use with various kinds of arrays, and reproduca- 

 ble. In this context, more accurate transducers are 

 coveted by the researcher. New developments in 

 this field primarily include the strain gauge trans- 

 ducers for unlimited depth measurements with an 

 accuracy of + 1 foot in 1 ,000 feet. The strain gauge 

 principle has merit because it is more feasible to use 

 a pressure sensitive device (in an environment 

 where the pressure varies from 0.44 to 0.46 psi per 

 foot of depth) and then convert pressure to depth. 



Conductivity/ 

 Salinity 



Sea Water 

 Sampler 



Nansen Bottle 



Volumetric Method 

 (Titration) 



Conductivity Bridge 

 Salinometer (Uni- 

 versity of Wash- 

 ington) 



Sahnity Accuracy: +0.02 part 

 per thousand 



Salinity Accuracy: +0.005 part 

 per thousand 



Repeatability: +0.001 part per 

 thousand 



Is not continuous; requires la- 

 borious analysis of samples 



Electrical Method 



Conductivity Cell 

 Foxboro Company 

 Serfass Bridge 



Accuracy: ±0.1 part per thou- 

 sand 



Accuracy: + 1.0 part per thou- 

 sand (0.1 part per thousand if 

 calibrated before and after use) 



Becomes unstable because of 

 change in cell characteristics; 

 actual measurements are 

 largely empirical in nature 

 and a basically incorrect as- 

 sumption is technically made 

 that the ocean water composi- 

 tion is constant 



Although measuring techniques being used for 

 salinity in situ and probes for conductivity are 

 deemed by some as "acceptable," many suggestions 

 for improvement in this field have been put forth to 

 provide accuracy for use in coastal waters — porta- 

 bility of the equipment, automated collection equip- 

 ment, sensor capability of 20-40 parts per thousand 

 ocean salinity range, accuracy + .001 part per 

 thousand (classical hydrography demands salinity 

 measurements approximately ± .01 per cent rela- 

 tive), equipment capable of easy calibration and 

 alignment, non-polarized electrodes, etc. Miniatur- 

 ized transistor salinometers, conductivity-tempera- 

 ture indicators, temperature-chloririty titrators, 

 neutron absorption, salinity-temperature-depth 

 recorders, etc., are also being used to some extent by 

 various activities. 



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