SYSTEM MEASUREMENT ERRORS 



The primary temperature standard for this study is comprised of the hydrocast 

 temperature measurements. Several complete hydrocasts were made during the Gulf of 

 Alaska, SUDS I, and CAPER experiments. During the RAPLOC/DEEPTOW experiments, 

 no complete hydrocasts were obtained. However, on nine CTD/SV profiles, a hydrocast 

 sampling bottle and thermometers were attached to the CTD/SV cable just above the 

 CTD/SV sensor package. At the maximum depth of the CTD/SV profile, a hydrocast 

 temperature and depth measurement were obtained. In addition, a water sample was taken 

 to provide a salinity measurement. Simultaneous CTD/SV temperature, salinity, and depth 

 measurements were made. Similar measurements also were made on some of the Gulf of 

 Alaska and SUDS I STD/SV profiles and on some of the CAPER CTD/SV profiles. No 

 hydrocast measurements were made during the ORB-3 and ORB-4 experiments. For these 

 data sets, the STD/SV sensor measurements are used as the standard for determining the 

 XBT system errors. 



This section compares the STD/SV, CTD/SV, SVTP, XBT, thermistor chain, towed 

 thermistor, and bucket thermometer temperatures with the hydrocast measurements, and 

 determines the corrections required to bring these measurements into agreement with the 

 hydrocast measurements. The corrections are referred to as system errors. Once a system 

 error is determined, it is used in all subsequent comparisons. Thus all system errors deter- 

 mined in the following analyses are referenced to the hydrocast temperatures. 



The generally accepted accuracy of the hydrocast temperature measurement is 

 ±0.02°C. 



STD/SV, CTD/SV, AND SVTP SYSTEM ERRORS 



During the Gulf of Alaska experiments, temperature accuracy checks were obtained 

 on three hydrocasts and, at maximum depth, on seven STD/SV profiles. Table 7 summar- 

 izes the differences between STD/SV temperatures and hydrocast temperatures for depths 

 greater than or equal to 1000 m. To obtain the right-hand column of differences, the 

 hydrocast sample bottles and thermometers were attached on the same cable as the STD/SV 

 sensor package. Thus these differences are the result of essentially simultaneous sets of 

 measurements. Table 8 summarizes the seven temperature comparisons obtained at the 

 maximum profile depth. On STD/SV 40, two sample bottles were placed one above the 

 other to obtain the two independent comparisons. An inspection of the differences tab- 

 ulated in tables 7 and 8 shows that for depths greater than or equal to 1000 m, the differ- 

 ences vary randomly about 0.00°C. It is concluded that the Gulf of Alaska STD/SV system 

 error is zero. 



No hydrocast measurements were made at the time the Gulf of Alaska SVTP 

 measurements were made, so no direct comparisons between hydrocast and SVTP measure- 

 ments were possible. In water mass 2, the temporal and spatial variabiHty in temperature 

 for depths greater than 200 m was small. The maximum depth of the SVTP profiles was 

 600 m. At this depth, the average of 1 5 SVTP measurements was 3.32°C with a standard 

 deviation of 0.04°C. The average of 41 STD/SV measurements was 3.29°C with a standard 

 deviation of 0.03°C. On the average, at 600 m, the SVTP measured a water temperature 

 0.03°C higher than the STD/SV. It is concluded that the Gulf of Alaska SVTP system 

 error is -0.03°C. 



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