Thus, comparisons using reversing thermometer observations as absolute 

 reference temperat\ires should be quite meaningful. However, it is recog- 

 nized that reversing thermometer observations may contain some bias. A 

 survey ship is generally rolling during the approximately 5 minutes required 

 for a reversing thermometer to adjust to its surroundings. Thus, the 

 thermometer is not located within the same water mass but is continually 

 moving vertically through a column of water. The observation is actually 

 an average temperature taken over a 5- to 10-minute period within a water 

 column as much as 3 meters in thickness. 



Reversing thermometer temperatures were tabulated for each cruise. 

 Temperatures were also measured with several other instruments, including 

 an injection thermometer (read by ship's engineer and an oceanographer) , 

 bucket thermometer, BT (read in the field), BT (uncorrected print), and BT 

 (TCS added). 



Reversing thermometer observations and comparative observations 

 were generally made within 10 minutes of each other; however, some 

 paired observations were taken as much as one-half hour apart. 



Means, standard deviations, and confidence limits (t^g) of dif- 

 ferences between simultaneous observations made with various tempera- 

 ture sensors are presented in table 5» The mean difference between 

 reversing thermometer and bucket thermometer observations during all 

 cruises was slightly less than .5°F. Mean bucket observations were 

 always lower than reversing thermometer observations. The mean differ- 

 ence between reversing thermometer observations and values measured 

 with a h\ill -mounted probe submerged 3 feet (DELTA IV and ECHO V) was 

 nearly .h'^F, only .1°F better than the bucket thermometer. However, the 

 standard deviation of differences was less than half that of the bucket 

 thermometers. Thus, it appears that thermistor probes give somewhat 

 more accurate and consistent reference temperatures than bucket ther- 

 mometers. 



Means and standard deviations of the differences for DELTA V and 

 ECHO V are slightly smaller than the mean results for all cnaises. This 

 apparently indicates that stabilization of bucket thermometers for about 

 k minutes introduces a slight error. 



The statistics of all cruises indicate that injection temperatures 

 exceed measured surface temperatures by reversing thermometers by about 

 1°F, approximately the same value found by Saur (reference 5)« With the 

 exception of DELTA II, injection thermometer obsejrvations were higher 

 than reversing thermometer observations. 



Saur hypothesizes that incrustation or fouling, poor exposure of 

 the well to water flow, possible air space within the well, and heat 

 conduction by metal fittings produce greater injection thermometer bias 

 than warming of the water before it reaches the thermometer well. Saur 

 also noted that each injection thermometer exhibited a trip bias, i.e, 

 the injection thermometer error varied from trip to trip. This varia- 

 tion was also indicated by data collected by the USCGC CEENCOTEAGUE 



12 



