temperature, is discussed in the section, Procedure for Determining XBT System Error. The 

 author agrees that the procedure Sippican now recommends will materially improve the 

 accuracy of XBT measured temperatures. In the future, this should become a part of the 

 standard operating procedure for making XBT measurements. 



NOTEC 



The author recognizes the importance of a depth error on the temperature at any 

 depth, and that its contribution to the temperature error is a function of the magnitude 

 of the vertical temperature gradient at the depth under consideration. The 200-, 300-, and 

 400-m depths were selected for comparison since, for all data sets, these were below the 

 thermocline where vertical gradients are smaH. 



Using Sippican's depth error of ±15 ft (4.6 m) from the surface to 230 m and ±2% 

 for depths greater than 230 m, temperatures were measured at 200 ±4.6, 300 ±6.0, and 

 400 ±8.0 m for selected XBT profiles made in each of the water masses where measurements 

 were made. The vertical temperature gradients at 200, 300, and 400 m were computed 

 from these measurements. In the following tabulation of these gradients, the units are °C/m. 



Depth, m 



200 



GULF OF ALASKA 



Water mass 2 0.000 



Water mass 7 -0.007 



Transition water mass 0.001 



SUDS I 1972 



Area A -0.009 



AreaC -0.038 



ORBS -0.017 



ORB 4 -0.009 



CAPER 



Water mass 1 -0.024 



Water mass 2 -0.010 



Water mass 3 -0.001 



RAPLOC/DEEPTOW -0.024 



300 



400 



0.001 



0.004 



0.000 



-0.001 



0.001 



0.001 



-0.007 



-0.004 



-0.012 



-0.005 



-0.018 



-0.007 



-0.014 



-0.007 



■0.013 



-0.020 



-0.013 



-0.017 



■0.008 



-0.016 



-0.004 



-0.005 



It is believed that the overall contribution of the system depth error to the 

 temperature error at 200, 300, and 400 m is minor compared to other factors contributing 

 to the observed temperature differences. 



141 



