TEMPERATURE ACCURACY OF 1830-m SYSTEMS 



During the CAPER and RAPLOC/DEEPTOW experiments, twenty-six 1830-m XBT 

 profiles were attempted. Of the eight profiles made during CAPER, one was a catastrophic 

 failure and seven were successes. Of the 1 8 profiles made during RAPLOC/DEEPTOW, 

 seven were catastrophic failures, three were successes, seven were partial successes, and one 

 exceeded the Cahbration correction of ±0.34°C. The eight catastrophic failures were all 

 related to an apparent temporary insulation failure in the upper 50 m of the profile. Since 

 no independent temperatures were measured concurrent with the CAPER XBT measure- 

 ments, an analysis of their accuracy was not possible. However, on the basis of information 

 available, there was no reason to question the validity of the seven visually acceptable 

 profiles. An examination of the RAPLOC/DEEPTOW 1830-m profiles showed that in spite 

 of apparent temporary insulation failure, some of the catastrophic failures and partial 

 successes appeared to record vaUd temperatures for some depth intervals. However, compar- 

 ison with CTD/SV measured temperatures showed that several of these profiles measured 

 temperatures markedly different from the CTD/SV temperatures for depths greater than 

 that of the first indication of insulation failure. For the three successful XBT profiles, the 

 temperatures measured at standard hydrocast depths from 200 to 1500 m were compared 

 with the average CTD/SV measured temperatures. The differences varied from -0.25°C 

 to 0.09°C. 



COMPARISON OF SIMULTANEOUS XBT PROFILES 



During the ORB-3 and RAPLOC/DEEPTOW experiments, 96 pairs of simultaneous 

 460-m XBT profiles were attempted from the ORB, with 20 pairs made under tow at 

 5 knots and 76 at anchor. During the RAPLOC/DEEPTOW experiments, eighteen 1830-m 

 profiles were attempted simultaneously with 460-m profiles taken on two different 460-m 

 systems. The number of visually acceptable pairs of 460-m profiles was 90, and the number 

 of visually acceptable triplets was 10. These data were used to examine the relative 

 accuracy of 460-m and 1830-m XBT systems. Temperatures at standard hydrocast depths 

 and near-surface-layer depths were compared. Comparisons were made for depths in the 

 near-surface layer, in the thermocline, and below the thermocline. 



The 460-m comparisons showed that 43 (47.8%) pairs of the 90 pairs satisfied the 

 ±0.34°C accuracy specification at all comparison depths; 62 (68.9%) satisfied the accuracy 

 specifications at all in-layer and below-thermocline depths; and 28 (31.1%) pairs did not 

 satisfy the accuracy specification at one or more in-layer and below-thermocline depths. 

 For nine (10.0%) pairs, the near-surface-layer depth difference exceeded the ±5-m accuracy 

 specification; for 81 (90.0%) pairs, it was less than the accuracy specification. For both 

 sets of comparisons, considerably more differences were positive than negative. 



In each set of comparisons, one of the systems consistently measured a higher 

 temperature than the other. Of a total of 1 1 1 6 comparisons, the absolute value of the 

 differences exceeded 0.34°C for 16.6% of the comparisons. 



An examination of individual pairs of profiles showed that many of the pairs 

 differed by large amounts. Some pairs measured large differences starting in the near- 

 surface layer, with the difference being a variable function of depth; while other pairs 

 agreed identically in the near-surface layer and began to differ at some depth below the 

 thermocline, with the difference being an increasing function of depth. Figures 43 to 



130 



