D. PRESENT DEVELOPMENT OF TEMPERATURE- DEPTH 

 INSTRUMENTS 



The most promising developments in instrumentation to measure 

 temperature at depth are the Snodgrass-type BT and the Richardson 

 chain. Basically the Snodgrass instrument senses temperature with a 

 thermistor and depth with a vibrating wire transducer. A Wein bridge 

 converts temperature electronically from a resistance change to a 

 varying frequency, and the transducer is basically a frequency- 

 sensitive device. The frequencies for temperature and depth are 

 transmitted to the ship by a single conductor cable with a sea water 

 return. These frequencies are then fed to a magnetic tape recorder 

 and/ or filtered on deck, digitized and converted to temperatures, or 

 they may be converted to voltages and fed to an x-y recorder. The 

 Snodgrass-type BT can give a continuous picture of the temperature 

 structure with depth. 



The Richardson chain is essentially a series of thermistors at 

 fixed intervals on a cable which is suspended from a ship to make 

 continuous observations of temperature with time at several fixed 

 depths. The resistances of the sensing elements- are detected sequent- 

 ially and either recorded on a potentiometer strip chart recorder or 

 digitized with a shaft position encoder and recorded on punch cards. 



The techniques represented by these two instruments are at the 

 present time the most promising for measuring ocean temperature at 

 varying depths and at fixed depths with time. 



E. CONCLUSIONS AND RECOMMENDATIONS 



Requirements exist for a number of temperature measuring instru- 

 ments. These instruments fall into two categories: either routine or 

 survey. The fundamental differences between these two categories 

 are that routine instruments must be simple and rugged for use by 

 nonscientific observers in routine observations, whereas survey instru- 

 ments must provide a high order of data accuracy for use by scientific 

 observers in special observations. Instruments in the routine category 

 are the standard bathythermograph, a hull- mounted temperature probe, 

 an air droppable telemetering BT, and an electronic helicopter BT. 

 Instruments in the survey category include an electronic bathyther- 

 mograph (single sensor, temperature continuous with depth), a ther- 

 mocline recorder (multiple sensors, temperature continuous with 

 time), and an airborne radiation thermometer. 



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