on seven different 460-ni systems. Surface temperature comparisons showed that two of 

 the systems, after making a series of accurate profiles, malfunctioned. Comparison of 

 400-m temperatures showed that the malfunction did not result in a simple temperature 

 displacement of the profile. Consequently, it produced profiles having systematic errors 

 in the vertical temperature gradients. The profiles made after the system malfunctioned 

 were visually acceptable profiles. Of 736 profiles 36.5 percent were made by the mal- 

 functioning systems. 



• Of a total of 1961 attempted 460-m profiles, the following percentages apply: 



Visually acceptable to the maximum depth 80.1% 



Partially successful 10.8% 



Catastrophic failures 6.4% 



Miscellaneous failures 2.7%. 



• Of a total of 5 18 460-m XBT profiles made when the XBT systems were not 

 malfunctioning, only 37.8 percent of those reaching 400 m satisfied 200-, 300-, and 400-m 

 accuracy criteria at all three depths and 19.9 percent failed to satisfy the accuracy criteria 

 at all three depths (see table 32). The accuracy criteria were based on average hydrocast 

 and STD/SV temperatures. 



• Comparison of XBT temperatures with average hydrocast and STD/SV 

 temperatures, quasisimultaneous STD/SV temperatures, and thermistor chain temperatures 

 taken underway at 3 knots showed that the 460-m XBT systems measured, on the average, 

 temperatures that were higher and vertical temperature gradients that were larger than those 

 measured by the other systems. Once the profiles associated with the large differences 

 were identified and removed from the data set, the remaining profiles accurately measure 

 the temperature. For this data set, the average differences were near zero with standard 

 deviations of 0.07°C to 0.1 3°C. 



• Of a total of 559 profiles made when the XBT systems were not malfunctioning 

 and also were reaching a minimum depth of 200 m, the 200-, 300-, or 400-m temperatures 

 for 54 (9.7 percent)of the profiles exceeded the average hydrocast and STD/SV temper- 

 atures by more than or equal to ±0.50°C at one or more of the three depths. 



• The data set included 26 attempts to make 1830-m XBT profiles. Of the 26 

 attempts, 10 were successes, 7 were partial successes, 8 were catastrophic failures, and one 

 exceeded the calibration correction. The catastrophic failures were so classified because 

 of apparent temporary insulation failure in the upper 50 m. The measurements made at 

 depths greater than the apparent insulation failures for some profiles appear accurate. 

 However, use of these measurements without other confirming measurements for depths 

 greater than the first insulation failure may result in some risk. 



• "Runs" of consecutive XBT profiles were observed in which the temperature 

 measurements are accurate within prescribed limits. However, the measurements do not 

 vary randomly within these hmits and form a statistical run of biased data. 



• Comparison of 90 pairs of simultaneous visually acceptable 460-m XBT profiles 

 at standard hydrocast depths indicated the following: 



132 



