• Cf 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 cahbration 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 limits and form a statistical run of biased data. 



• An examination of individual simultaneous pairs of visually acceptable 460-m 

 profiles showed that many of the pairs differed by large amounts. Some of the pairs measured 

 large differences starting in the near-surface layer with the differences being a variable func- 

 tion of depth while others 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. 



• During the SUDS I experiments, 28 XBT profiles were judged by the observer to 

 be visually acceptable and were digitized and transmitted to the Fleet Numerical Weather 

 Center where they were used as inputs to predictions of Fleet sonar performance. Of the 

 28 profiles, 15 were made in area C, where enough hydrocast and STD/SV measurements 

 were taken to establish an average 200-, 300-, or 400-m temperature. Of the 15, 13 reached 

 a depth of 400 m. Of those reaching 400 m, the percentages satisfying the 200-, 300-, and 

 400-m accuracy criteria at the various depths were as follows: 



All three depths: 3, or 23.1% 



Two depths: 2, or 15.4% 



One depth: 3, or 23.1% 



No depths: 5, or 38.5%. 



If this sample of 13 XBT profiles is representative of the data being transmitted to FNWC 

 on a routine basis, the inclusion of many visually acceptable but actually erroneous measure- 

 ments must certainly have an adverse effect on the accuracy of the acoustic predictions 

 based on these measurements as inputs to the predictions. 



RECOMMENDATIONS 



• As a result of its review of these studies, the Sippican Corp suggests that the 

 following procedure be used for those applications requiring retention of full available 

 system accuracy. 



". . . calibrate with an A2A test canister whenever (1) a new 

 roll of chart paper is installed, (2) at four-hour intervals during 

 continuing drops, and (3) whenever the 2-second, midscale 

 calibrate trace exceeds ±.1°C from 16.7°C. In addition, a once 



