temperature-gradient errors, sound-speed gradient errors, sink-rate and depth errors, and the 

 adequacy of a temperature profile unaccompanied by a salinity profile for sonar range 

 predictions were studied. 



In 1977, the Naval Research Laboratory published a memorandum report discussing 

 subtle malfunctions of the 460-m (T-4 probes) XBT systems. The report stated: 



"Malfunctions such as that exhibited in this report have been 

 observed, identified, and tallied in several multi-ship experi- 

 ments. The results are rather startling, in that most of the 

 T4 malfunctions actually are subtle and easily could slip by 

 the uninformed operator." 



Their analysis discusses possible causes of the malfunction. They also state that the 

 malfunction was only positively identified in two batches of probes and that, "further 

 extrapolation to it being a general Fleet problem is open to speculation." 



On 22-23 October 1977, the Naval Underwater Systems Center conducted an 

 accuracy study of the T^ XBT probe. The primary purpose of the test was to identify 

 which portions of Navy stock XBT probes were unsuitable for tactical Navy use. They 

 used 1250 probes from Navy stock and 264 probes purchased from the manufacturer. They 

 sorted the XBT profiles into five mutually exclusive categories. Two of the five categories 

 were analogous to the XBT profiles that the Naval Research Laboratory study (ref 4) 

 referred to as containing "subtle malfunctions." A considerable number of the profiles 

 were in these two categories. 



Beginning with the Naval Undersea Center's Gulf of Alaska acoustic experiments in 

 1971, the author began accumulating XBT temperature profiles as well as supporting 

 temperature measurements, with the objective of examining the accuracy of routinely 

 acquired XBT temperature profiles. The purpose of this publication is to report the results 

 of these studies. 



This report includes discussions of the following studies of 460-m XBT system 

 temperature measuring accuracy: 



a. Determination of system errors for the various temperature measurement 

 systems used. 



b. Comparison of XBT surface temperature measurements with indepen- 

 dent surface temperature measurements. 



c. Two comparisons of XBT measured temperatures with average hydrocast 

 and STD/SV measured temperatures. 



d. Comparison of XBT measured temperatures with quasisimultaneous 

 STD/SV measured temperatures. 



e. Comparison of XBT measured temperatures with simultaneous thermis- 

 tor chain-measured temperatures. 



f. Discussion of selected individual XBT profiles. 



4. Naval Research Laboratory Memorandum Report 3612, Subtle T4 XBT Malfunctions, by J.P. Dugan 

 and A.F. Schuetz, September 1977. 



5. Naval Underwater System Center, letter report Ser 8431-17, 13 February 1978. 



