The system errors for the STD/SV, CTD/SV, SVTP, and thermistor cham systems 

 were all small - varying from -0.03°C to 0.02°C. The errors for the towed thermistor and 

 the bucket thermometers were slightly larger — varying from -0.1 1°C to 0.08°C. The 

 system error for the towed thermistor, used during the Gulf of Alaska experiments, changed 

 from 0.08°C to -0.1 1°C between the measurements made during the A2 experiments and 

 those made during environmental survey 2. This may have resulted from a recalibration of 

 the system between the two sets of measurements. 



Some of the XBT system errors were substantial — varying from -0.1 9°C to 0.23°C. 

 These errors are fixed. To be certain that the absolute value of the temperatures recorded 

 by a given XBT system is accurate, it appears necessary to determine the XBT system 

 error. To do this, independent and simultaneous temperature measurements are required. 

 In the absence of these latter measurements, the absolute value of the XBT recorded 

 temperature is questionable to within approximately ±0.2°C. 



SURFACE TEMPERATURE ACCURACY OF 460-m SYSTEMS 



Independent surface temperature measurements were made at the same time XBT 

 profiles were made during the Gulf of Alaska, SUDS I, CAPER, and RAPLOC/DEEPTOW 

 experiments. A few measurements were made by using the hydrocast and STD/SV systems. 

 Most of the measurements were made by means of a towed thermistor (Gulf of Alaska), 

 thermistor chain (SUDS I), and bucket thermometers (CAPER and RAPLOC/DEEPTOW). 

 A total of 736 XBT profiles were made, together with one or more independent and 

 simultaneous surface temperature measurements. 



The purpose of these m.easurements was to check the surface temperature 

 measurement accuracy of visually acceptable XBT profiles. As the analysis proceeded, a 

 secondary purpose was reahzed. This was to use the independent measurements as detec- 

 tors of malfunctioning XBT systems. Two malfunctioning systems were detected. The 

 first system was used to make the Gulf of Alaska measurements. Comparison of the XBT 

 surface temperatures with the towed thermistor temperatures showed that the XBT system 

 began to malfunction when making XBT profile 166. Of a total of 327 profiles, the 

 accuracy of the XBT surface temperature was questionable for 162 (49.5%) profiles. The 

 malfunction of this system was not detected until the preparation of this study some 6 years 

 after the data were pubhshed. The second system was used by the MOANA WAVE 

 during the CAPER experiments. Comparison of the XBT surface temperature with the 

 bucket temperatures showed that the MOANA WAVE XBT system began to malfunction 

 when making XBT profile 46. Of a total of 1 38 profiles, the accuracy of the surface 

 temperature was questionable for 103 (74.6%) profiles. The cause, or causes, of either of 

 the malfunctions are not known. The malfunction of these two systems would not have 

 been discovered if independent surface measurements had not been made. 



An analysis of the 400-m temperatures showed that the malfunctioning systems did 

 not shift the profile by a fixed amount. The 400-m differences were not the same 

 magnitude as the surface differences. 



Once the profiles made when the XBT systems were malfunctioning were detected 

 and removed from the data set, the XBT and independently measured surface temperatures 

 were in agreement. The average of 467 comparisons was 0.02°C with a standard deviation 

 of 0.15°C. The distribution of the differences was slightly biased, with 56.5% being positive, 

 38.6% negative, and 4.9% zero. 



127 



