ERRORS RELA'IED TO DIGITIZED BT DATA 



BT's in original stored form are not adaptable to high-speed computer 

 analysis techniques. A punchcard format vas developed for analysis of 

 these data. Reading, coding, and punching of BT's on IBM cards introduce 

 additional potential sources of error. These errors may be divided into 

 two classes: (l) gross reading or key-punch error and (2) small reading 

 variations. Key-punch operators generally have highly efficient verifi- 

 cation techniques. Therefore, no attempt was made to separate and evaluate 

 this type of error. 



Hazelworth (reference l) described the SERC punchcard format which 

 has been used by the Naval Oceanographic Office for several research proj- 

 ects. The SERC punchcard contains water temperatxire in degrees and tenths 

 (Op) at 20-foot intervals to 360 feet and at to-foot intervals at greater 

 depths. A study of a large number of punchcards indicated that the most 

 common type of error made by the reader-coder was inaccuracy in reading 

 the temperature by 5° or 10°F. Errors of this magnitude can significantly 

 influence a statistical analysis and must be eliminated. A computer can 

 be programmed to filter them out. 



In order to evaluate coding error and reading accuracy, 100 to 200 

 bathythermograms from each of five ocean weather stations that were coded 

 and on punchcards were reread by several readers. The means and standard 

 deviations of differences between the two readings were computed (table 7) • 



TABLE 7 



MEANS AND STANDARD DEVIATIONS OF DIFFERENCES BETWEEN 

 TWO READINGS OF THE SANE BATHTTHERMOGRAMS 



Ocean 

 Weather 

 Station 



Number of 



Individual 



Readings 



BRAVO 



1736 



CHARLIE 

 DELTA 

 ECHO 

 HOTEL 



2751 

 1586 

 3081 

 6086 



Mean 

 Differences 



.039 



.072 

 .076 

 .246 

 .063 



Standard 

 Deviation 



of 

 Differences 



.07 

 .18 



.10 



.31 

 .Ik 



Table 7 indicates that different individuals usually read BT prints 

 with a variation of less than .1°F. Some variation can be attributed to 

 differences in reading ability and to the inconsistent quality of BT prints. 



CONCLUSIONS 



The object of this study was investigation of the accxiracy of BT 

 Instruments used in routine svirvey operations. All observations were taken 

 by trained oceanographers using accepted avirvey procedures to record the 

 thermal structure with a maximum degree of accuracy. No attempt was made 



17 



