COMPARISON WITH TOWED THERMISTOR 



During the Gulf of Alaska experiments, surface temperatures were continuously 

 measured during environmental surveys 1 and 2 and during propagation loss experiments 

 Al , A2, and A3 by using a single towed thermistor bead. During the time these measure- 

 ments were made, 334 XBT profiles were obtained. The seven XBT profiles whose calibra- 

 tion lines deviated for 16.7°C by more than ±0.34°C are not used in the following analysis. 

 In addition, 82 STD/SV profiles were made at the same time the towed thermistor measure- 

 ments were made. 



The differences between the towed thermistor measurements and the XBT (•), 

 STD/SV (x), and SVTP (x) temperatures are plotted versus the XBT consecutive number 

 in figure 15.* Also indicated are the dates of the acoustic events. A visual inspection of 

 figure 15 shows that from XBT 1 to 165 the differences vary randomly about zero. However, 

 for all XBT profiles after 165, all differences except for 14 are negative and there is a larger 

 variation from difference to difference. In contrast, the STD/SV and SVTP differences vary 

 randomly about zero during the entire time period that XBT 1 to 334 were taken. 



Pertinent statistics for the comparisons presented in figure 15 are summarized in 

 table 20, and figure 16 contains ogives of the differences for XBT 1 to 165 and XBT 166 to 

 334. The differences for XBT 1 to 165 are normally distributed with a near-zero mean and 

 a standard deviation of 0.15°C. In contrast, the distribution of the differences for XBT 166 

 to 334 is skewed. The mean value is -0.3 1°C, with 148 (91.4%) of the differences negative 

 and 12 (7.4%) positive. STD/SV profiles 1 to 41 were made during the same time interval 

 that XBT profiles 1 to 165 were made, and STD/SV profiles 42 to 93 and SVTP profiles 94 

 to 1 17 were made during the same time interval that XBT profiles 166 to 334 were made. 

 The average differences between the 80 STD/SV and SVTP surface temperatures and the 

 towed thermistor surface temperatures were near zero (actually 0.007°C) with a standard 

 deviation of 0.05°C. For these comparisons, it is concluded that the XBT system was not 

 operating properly when XBT profiles 166 to 334 were made.** 



The largest negative difference between the XBT and towed thermistor measure- 

 ments was -1.15°C.*** This difference was measured by XBT 288, which is shown in 

 figure 17. The towed thermistor surface temperature was 9.06°C, which, correcting for 

 system errors, would be 8.89°C on the XBT 288 grid. An inspection of figure 1 7 reveals 

 that the profile has a poorly defined surface depth. The XBT surface temperature was read 

 at 8.07°C on the grid. Thus this large difference may be an artifact of the poorly defined 

 surface depth. The next largest negative difference of-0.69°C was associated with XBT 302. 

 This profile is shown in figure 18. In this case, the surface depth is well defined. On the 

 grid, the towed thermistor temperature was 10.65°C. Thus this surface temperature 



*The consecutive numbers for which differences are missing are those associated with XBT profiles 

 calibration lines differed from 16.7°C by more than ±0.34°C. 



''*The improper operation of the XBT system was not detected until the XBT surface temperatures were 

 compared with the towed thermistor surface temperatures. This comparison was not made until the 

 preparation of this report, some six years after the publication of reference 6. In the preparation of 

 reference 6, the XBT profiles made when the XBT system was not operating properly were accepted 

 as being correct profiles and published. In appendix B of reference 6, all XBT profiles listed after 

 XBT 224 (19 June 1971, 0400 LST) were made with the impropedy operating system. 



"♦This difference is not plotted on figure 15 due to the scale but is plotted on figure 16. 



42 



