400 m. The two sets of measurements agree reasonably well from the surface to about 

 60 m. From 60 m to the maximum depth, the differences increase systematically from near 

 zero to 0.97°C at 400 m. In an acoustic application, the difference between these two 

 profiles is significant since the XBT profile suggests the presence of a depressed channel 

 that is considerably stronger than the channel suggested by the STD/SV profile. 



Table 36 presents a statistical summary for the set of all visually acceptable profiles 

 and for profile set I for comparisons of surface, 200-, 300-, and 400-m measurements. For 

 the set of all visually acceptable profiles, the results are similar to those obtained in the two 

 studies previously discussed. The major difference is the standard deviations, which are 

 somewhat larger than those listed in appendices B and C. For profile set I, the average 

 differences are all positive and a greater percentage of differences is positive than was the 

 case for all visually acceptable profiles. These data give additional evidence supporting the 

 conclusion that, on the average, the XBT system measures temperatures slightly higher than 

 those measured by other measuring systems. 



Depth, 

 m 





Difference, °C 



Percent 



n 



AT 



s 



Positive 



Negative 





ALL VISUALLY ACCEPTABLE PROFILES 









63 



-0.110 



0.67 



55.4 



41.3 



200 



66 



0.049 



0.75 



50.0 



47.0 



300 



64 



0.060 



0.74 



48.4 



46.9 



400 



62 



0.090 

 PROF 



0.74 

 ILE SET I 



51.6 



43.5 







46 



0.060 



0.16 



67.4 



28.3 



200 



46 



0.082 



0.21 



56.2 



39.1 



300 



45 



0.077 



0.22 



55.6 



40.0 



400 



43 



0.073 



0.20 



58.1 



34.9 



Table 36. Summary of comparisons between quasisimultaneous 

 XBT and STD/SV profiles. 



COMPARISON WITH THERMISTOR 

 CHAIN MEASUREMENTS 



The fourth study compares simultaneous XBT and thermistor chain measurements. 

 These measurements were made during the SUDS I experiments. On 23 February 1972, 

 with the thermistor chain vertical in the water (zero tow speed), seven XBT profiles were 

 attempted between 0650 and 0726 LST. On 12 February 1972 at 0428 LST, one XBT 

 profile was made under similar circumstances. These pairs of measurements are the most 

 accurate set considered in this study since they are as close to simultaneous in space and 

 time as is possible to obtain at sea, and were made with the vessel hove to and drifting, and 

 with the thermistor chain hanging vertically in the water. During the acoustic experiments, 

 the LEE, towing the thermistor chain at three knots, made 153 XBT temperature profiles. 



77 



