measurements, there would be no reason to consider the XBT 55 A profile incorrect at 

 depths less than 440 m. Of special interest to underwater acoustics is the vertical temper- 

 ature gradient biasing nature of the differences, with the differences increasing with 

 increasing depth from about 60 to 440 m. 



In summary, a set of profiles (from profile set I) that reached a minimum depth of 

 200 m and whose temperatures exceeded the average hydrocast and STD/SV temperatures 

 by equal to or more than ±0.50°C at 200, 300, or 400 m, was compiled. This set contained 

 54 profiles, which was 9.7% of the total set of 559 profiles used in this analysis. An exam- 

 ination of these data showed positive differences as large as 3.02°C, negative differences 

 as large as -0.73°C, positive temperature gradient biases as large as 0.96°C/100 m, and 

 negative temperature gradient biases as large as -0.73°C/100 m. 



TEMPERATURE ACCURACY OF 1830-m SYSTEMS 



During the CAPER and RAPLOC/DEEPTOW experiments, a limited number of XBT 

 profiles was obtained with two different 1830-m XBT systems. During RAPLOC/DEEPTOW, 

 18 profiles were made from the ORB at anchor, and during CAPER, eight profiles were 

 made from the FLIP at anchor in a three-point moor. Although the sample of 26 profiles 

 is small, a discussion of these measurements provides some preliminary information on the 

 performance of the 1830-m system. 



During the RAPLOC/DEEPTOW experiments, simultaneous surface temperatures 

 were also measured by a bucket thermometer concurrent with 10 XBT profiles and by the 

 CTD/SV system concurrent with three profiles. These 1 3 comparisons showed excellent 

 agreement between the XBT surface temperatures and the independently measured temper- 

 atures. The average of the 13 differences was 0.005°C, with the differences varying from 

 -0.14°Cto+0.12°C. 



A visual examination of the RAPLOC/DEEPTOW 1830-m profiles showed that 

 seven (38.9%) profiles were catastrophic failures, three (16.7%) profiles were successes, and 

 seven (38.9%) profiles were partial successes. For one profile, the calibration correction 

 was 1 .1 2°C, greatly exceeding the maximum allowed value of ±0.34°C. Figure 38 is a copy 

 of XBT 14C, one of the successful profiles; ie, visually acceptable to the maximum depth of 

 1830 m. The differences between the XBT measured and the average CTD/SV measured 

 temperatures for the three successful profiles are listed in table 41 . For all comparisons 

 except XBT 14C at 500 m, the differences were less than ±0.24°C. 



The seven XBT profiles classified as catastrophic failures (ie, no usable temperature 

 measurements for depths greater than 50 m) were so classified because of indications that 

 the wiring insulation failed in the first 50 m of the profile. Figure 39 is a copy of XBT 9C, 

 one of the catastrophic failures. At 10 m there is an abrupt increase in temperature, or a 

 "ghtch," which suggests that the insulation was beginning to fail. However, at 30 m it 

 appears that the insulation had "healed" and that the probe was recording valid temper- 

 atures. As the measurement proceeded, the insulation appeared to fail at 110, 850, 938, 

 and 1635 m, but in each instance seemed to recover and record vaUd temperatures until 

 the insulation failed completely at 1720 m. The other six catastrophic failures showed 

 similar characteristics. There is a temptation to consider XBT 9C a vahd profile over depth 

 intervals between the apparent insulation failures. In fact, XBT 9C was originally classified 

 as a partial success. Table 42 lists the differences for the profiles originally considered 

 partial successes and subsequently reclassified as catastrophic failures on the basis of an 



96 



