the previous analysis. For the set of 528 visually acceptable profiles, the XBT measured a 

 surface temperature that, on the average, v^as 0.1 5°C less than the independently measured 

 surface temperatures. This resulted in an average positive temperature gradient bias in the 

 surface-to-200-m layer. Analysis of the 351 profiles remaining after the elimination of the 

 profiles made with the two malfunctioning XBT systems showed that at the surface, the 

 XBT profiles measured a temperature shghtly higher than the independently measured 

 temperature; that at 200, 300, and 400 m, the XBT profile still measured temperatures 

 slightly higher than the average hydrocast and STD/SV measurements; and that the vertical 

 temperature gradient from the surface to 200 m was slightly biased. 



Quasisimultaneous XBT and STD/SV profiles were obtained during the Gulf of 

 Alaska, SUDS I, CAPER, and RAPLOC/DEEPTOW experiments. A total of 66 pairs was 

 obtained. These measurements were used to further examine the accuracy of the XBT 

 measurements at the surface and at 200, 300, and 400 m. All measurements were made 

 with the vessel hove to and drifting or. in the case of the RAPLOC/DEEPTOW measure- 

 ments, at anchor. Of the 66 XBT profiles, 20 were made when the XBT systems malfunc- 

 tioned during the Gulf of Alaska and CAPER experiments. Recall that the system 

 malfunctions were only detected because independent surface temperatures were available. 

 The statistics for all the differences for each depth were very similar to the results obtained 

 from the two previous analyses. The major difference was that the standard deviations 

 were somewhat larger for this study. The statistics for the differences associated with the 

 profiles made when the systems were not malfunctioning are also similar to the statistics 

 for the two previous studies. 



During SUDS I simultaneous XBT and thermistor chain measurements were made 

 with the vessel both hove to and underway at 3 knots. Comparisons were made at 44 

 depths spaced 5.6 m apart from the surface to 242 m, the maximum depth of thermistor 

 chain measurements. While hove to and drifting, eight XBT profiles were attempted. Of 

 the eight, one was a catastrophic failure, one was a partial success, and six were successes. 

 For the seven profiles making measurements in the near-surface layer, the average values 

 for 16 comparisons were negative for five of the profiles and positive for two profiles. One 

 of the latter was the profile that was a partial success, having failed at 90 m. For the six 

 profiles making measurements below the layer, the average values were negative for five 

 profiles and positive for one. It was concluded that the seven probes used in this compar- 

 ison measured temperatures from the surface to 242 m that were slightly lower than those 

 measured by the thermistor chain. Only two of the six probes showed excellent agreement 

 in the statistical sense. The biasing of the differences may be related to a "run" of 

 consecutive probes. 



During the SUDS I stations 3 and 4 experiments, 73 XBT profiles were attempted 

 while the vessel was underway at 3 knots. Of the 73 attempts, 62 were successes, two 

 were partial successes, and nine were catastrophic failures. Comparisons, at the 44 

 thermistor chain sensor depths, of the 64 successful and partially successful profiles with 

 single thermistor chain temperature scans starting at the same time the XBT probe was 

 released, showed that three profiles were grossly in error and these were eliminated from 

 the data set. Further analysis of the remaining 61 profiles suggested that in the thermocline, 

 below the near-surface layer, the thermistor chain was measuring temperatures slightly 

 higher than the XBT measurements. This possibly resulted from a slight shoaling of the 

 thermistor sensors as a result of the 3-knot towing speed. Since the thermistor chain depth 

 sensor was inoperative, it was not possible to check this conclusion. Comparisons of the 



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