• Incorporate a depth sensor in test probes. 



Possible, but only with extensive design effort. When feasible, suggest location 

 over bottom of known depth and use of "glitch" occurring on chart paper as probe strikes 

 bottom as a depth check indicator.* 



• Identify possible "bad" traces before archiving data. 



Possible, through use of "second drops" in questionable cases. Still requires 

 training in judgement and/or supplying information on what trace should look like; 

 definitely a recommendation to pursue. 



• Eliminate causes of XBT system "failure." 



From the preceding discussion it appears that more extensive use of A2A and A4 

 testers will eliminate most of the apparent system failures encountered. The new MK8 

 recorder performs more "self-checking" but still requires a test canister to "know" the 

 launcher is "OK." As long as a launcher is required, a test canister should be used as often 

 as possible when full system accuracy is required. 



• Implement a precision digitizer and/or a more accurate display. 



Sippican MK8 or AN/BQH-7 systems provide precise recording of full digital data 

 on cassette storage for ease of data handling and includes a self-calibrated strip chart display 



AUTHOR'S NOTES RELEVANT TO SIPPICAN RESPONSE 



NOTE A 



In this section. Procedure for Determining XBT System Error, 200-, 300-, and 

 400-m temperature accuracy criteria intervals are defined. For convenience, these intervals 

 are referred to in the text as accuracy criteria. The accuracy criterion, as defined, is a 

 variable, being a function of depth, the average hydrocast temperature, and its variability 

 (table 13), the XBT system error (table 16), and the manufacturer's stated absolute value 

 of the accuracy of the XBT system converted to a standard deviation. The accuracy 

 criterion is not assumed to be ±0.24°C, a constant, but takes into account the variability 

 present in the various water masses where the hydrographic casts and XBT measurements 

 were made. 



For example, in the Gulf of Alaska at 200 m in water mass 2, the standard deviation 

 of 65 hydrographic cast measurements was 0.04°C, while in water mass 7 it was 0.67°C 

 for eight measurements (table 13). Thus the accuracy criterion at 200 m in water mass 2 

 was 3.88- 4.1 2°C and in water mass 7 was 4.11 - 5.47°C. If an XBT profile measured a 

 200-m temperature in water mass 2 that was within the above interval (0.24°C), it satisfied 

 the criterion. Likewise, if a measurement made in water mass 7 was within the appropriate 

 interval (1 .36°C), it also satisfied the accuracy criterion. 



NOTEB 



At the time of this analysis the procedure, recommended by Sippican and 

 concerning the use of the calibration line on the XBT profile for determining the measured 



*See author's note F. 



140 



