factor called TCS. (TCS = Mean reference temperature - Mean BT temperature) 



Reference temperatures are generally obtained with an injection ther- 

 mometer, although each BT is equipped with a small, inexpensive mercury 

 thermometer. During survey operations a more reliable mercury, "bucket" 

 thermometer is used. The TCS value, added to the surface temperature and 

 photographed with each bathythermogram, was assumed to represent instrument 

 bias and to be constant with depth. 



In order to obtain a quantitative measure of instrument bias variation 

 with depth and to obtain a clearer understanding of the effect of adding a 

 TCS, the means (X) and standard deviations (S.D.) of the differences between 

 the nine sets of paired BT observations were computed for several depths. 

 These data are presented in table k. The mean differences are also shown in 

 figixre 1(a and B). The first seven sets of observations have the TCS included 

 in the calculations. The National Oceanographlc Data Center has not included 

 the TCS factor in processing BT's since 1963» Thus the eighth and ninth sets 

 do not contain this factor. 



Analysis of table h indicates that the TCS generally improves the 

 mean sea surface temperature reading. Surface temperature differences 

 for the first through seventh sets of observations vary between 0.0° and 

 0.32°F, whereas the mean differences for the eighth and ninth sets are 

 O.Ul+° and 0.8l°F, respectively. The question arises of whether the TCS 

 decreases the differences between the two observations as depth increases. 

 The means (X) in table k indicate an improvement of about .2°F at all 

 depths. The samples used in this stucly are too small for valid conclusions. 

 Ideally, all nine sets of paired observations should have been processed 

 both with and without the TCS. 



The results also indicate that instrument bias varies with depth 

 and between pairs of instruments. The mean differences for the first 

 set of observations range from .31° at the surface to 1.30°F at i<-00 feet, 

 a difference of 1°F. Mean differences for the eighth set range from .37° 

 to .53°F, a difference of only .l6°F. The ninth set, which exhibited a 

 high correlation coefficient, has mean differences ranging from .^2° to 

 .8l°F, a difference of .39°F. 



COMPARISON OF TEMPERATURE SENSORS WITH REVERSIMG THERMOMETER DATA 



Several analytical comparisons between bucket, injection, and BT 

 temperatures (references k, 5) have qualitative conclusions which agree 

 with those of this report. However, since these analyses were not based 

 on absolute reference temperatures and assumed that bucket temperatures 

 were free of bias, their quantitative resiilts are limited. 



As indicated in table 2, 352 sea surface temperature observations 

 were recorded with reversing thermometers at DELTA and ECHO. In addition, 

 many reversing thermometer observations were made to a depth of 900 feet. 

 The reversing thermometer is considered to be an extremely accurate instru- 

 ment as free of instrioment bias as any temperature sensor presently avail- 

 able for oceanographic measurements. 



10 



