c. The vertical temperature gradient from tiie surface to 200 m is slightly 

 greater than that measured by the hydrocast and STD/SV systems for 

 the Gulf of Alaska and CAPER data sets, and slightly less for the 

 SUDS I and RAPLOC/DEEPTOW data sets. 



Thus, for this data set, the answer to the first question is yes, to the extent that there were 

 minor differences associated with three of the data sets. The answer to the second question 

 is also yes. 



For completeness, the results of the analysis of the profile set lA profiles are 

 summarized in appendix C and table 35. An inspection of these data shows that for all 

 five data sets at all depths, the average differences were close to zero, varying from 

 -0.023°C to 0.126°C with eight differences being positive and seven differences being 

 negative. The standard deviations were also small, varying from 0.03°C to 0.1 1°C. 



QUASISIMULTANEOUS XBT AND STD/SV 

 MEASUREMENTS 



The third accuracy study compares quasisimultaneous XBT and STD/SV profiles. 

 A total of 66 pairs of profiles, made within 30 minutes or less of each other, were obtained 

 during the Gulf of Alaska, SUDS I, CAPER, and RAPLOC/DEEPTOW experiments. These 

 measurements are used to examine further the accuracy of the XBT measurements at the 

 surface and at the 200-, 300-, and 400-m depths. All appropriate system errors were applied 

 prior to obtaining the differences between the two measurements. The results of the 

 comparisons were similar to those obtained from the first two studies. 



The individual differences are tabulated in appendix D. Tabulated are the XBT 

 numbers, the time in minutes between the beginning of the XBT and STD/SV measure- 

 ments, and the differences for the four selected depths. If the difference is positive, the 

 XBT temperature is higher than the STD/SV temperature, and if it is negative, the XBT 

 temperature is lower than the STD/SV temperature. In the Gulf of Alaska and CAPER 

 data sets, certain of the differences are underhned. These differences are associated with the 

 XBT profiles acquired when the LEE and MOANA WAVE XBT systems malfunctioned. 

 Recall that the malfunction of these systems was discovered from an analysis of the XBT 

 surface temperature measurement accuracy. 



Histograms of the differences listed in appendix D are shown in figure 27. The 

 dot-shaded areas are associated with the measurements made during CAPER when the 

 MOANA WAVE'S XBT system malfunctioned, the line-shaded areas are associated with 

 the measurements made during the Gulf of Alaska experiments, when the LEE's system 

 malfunctioned, and the unshaded areas show the differences associated with the remaining 

 profiles. An examination of figure 27 shows that at 200, 300, and 400 m, all but one of 

 the large differences are associated with the profiles made by the malfunctioning systems, 

 and that the differences associated with the Gulf of Alaska profiles obtained when the 

 XBT system malfunctioned would not have been detected from these comparisons since 

 these differences are similar in magnitude to the differences associated with the unshaded 

 areas. The profile associated with the largest unshaded 200-, 300-, and 400-m positive 

 differences shown in figure 27 is the Gulf of Alaska ESI -146 profile shown in figure 28. 

 The "dots" in figure 28 are the temperatures measured by STD/SV 39. These measure- 

 ments were made 30 minutes apart in the very stable water mass 2. Also shown are the 

 differences between the two sets of measurements at the surface and at 200, 300, and 



74 



