3. Establish a preliminary XBT system error by comparing XBT 200-, 300-, and 

 400-m temperatures with the hydrocast and/or STD/SV* temperature for quasisimultaneous 

 measurements.** In makmg this comparison, the appropriate STD/SV system errors are 

 appHed. If no comparisons were available, the preliminary system error was assumed to 



be zero. 



4. Establish the following 2 00- , 3 00-, a nd 400-m temperature accuracy criterion 



interval for each XBT system: T - e ± v S| + S2, where T is the average hydrocast and/or 

 STD/SV temperature for a given water mass, e is the preliminary XBT system error, sj is 

 the standard deviation of the average hydrocast and/or STD/SV temperature, and 

 S2 = 0.1 2°C, the standard deviation of the XBT system measurement accuracy. 



5. Compare each 200-, 300-, and 400-m XBT temperature with the accuracy 

 criterion interval to determine whether the criterion is satisfied. 



6. For each XBT system, compute the average 200-, 300-, and 400-m temper- 

 ature for all XBT profiles that satisfy the accuracy criterion at all three depths. *** 



7. Compare the average 200-, 300-, and 400-m XBT profile temperature with 

 the average hydrocast and/or STD/SV temperature to establish a final XBT system error. 



Average Hydrocast and/or STD/SV Temperatures 



The primary standards for comparison are the average temperatures measured by the 

 hydrocast and the STD/SV. Execution of step 1 establishes these temperatures. 



Since the temperature profile in the upper few hundred meters is different in 

 different water masses, it was necessary to first determine whether more than one water 

 mass was present in the area where the XBT profiles were obtained. In the Gulf of Alaska 

 area, three water masses were present. These were designated water mass 2, water mass 7, 

 and transition water mass (figure 2 and reference 1 1). The SUDS I data set includes 

 measurements made in areas A and C in different water masses (figure 3 and reference 7). 

 Since no hydrocasts or STD/SV measurements were made in area B, the area B XBT profiles 

 are not included in this study. The CAPER measurements were made in four water masses 

 designated water masses 1,2,3, and 4 (figure 5 and reference 1 0). Since only one STD/SV 

 measurement was made in water mass 4, no average temperatures could be established for 

 this water mass. The ORB-3, 0RB4, and RAPLOC/DEEPTOW measurements were made in 

 two water masses designated 1 and 2 (figure 4 and reference 8 and 9). However, most of the 

 measurements were made at anchor in water mass 2. The average temperature (T), the 

 number of observations (n), and the standard deviation (s) of the hydrocast and STD/SV 

 200-, 300-, and 400-m measurements are summarized in table 13. 



*In the discussion to follow, the designation STD/SV will be used collectively to refer to the STD/SV, 

 CTD/SV, and SVTP measurements. 

 **The independent surface temperature measurements are not used in this analysis because of the 

 difficulty of measuring precisely the surface temperature (see p 30-31 for detailed discussion). 

 ***The most accurate XBT profiles are the subset of the complete set of profiles that satisfies the accuracy 

 criterion at all three comparison depths. This subset is used to establish the final XBT accuracy criteria. 

 1 1 . Reference available to qualified requesters. 



26 



