Page 159 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

138 Maritime Archaeology: A Technical Handbook, Second Edition
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28 26 24 22 20 18 16 14
990206 990208
T1 T2 T3 T4 T5 T6 T7 T8
990210 990212 990214
Date decimal time (yymmdd.hh)
990220 990222
990224 990226
990216 990218
Transponders transposed
Correction error
Unknown
Spurious reading
Figure 4.23 Corrected depth measurements on the Pandora site.
analysis revealed a number of anomalies in these data that were useful in identifying the sources of errors. For example, note that the depths on Feb- ruary 7 are all systematically too small, indicating a possible error in the use of the tidal predictions. On February 11 it is almost certain that the operator has mistaken T2 and T3, on February 21 at T3 there is a spurious depth reading, and on February 22 there is an obvious anomaly in all but possibly one of the depth readings. These data were rerun using the new tidal corrections applied to all measurements. This resulted in a noticeable improvement in the depth and position residuals.
4. The Adjustment Program
Having developed the HPASSConvert program to a state where it was able to deal with the problems of the processing data from the diver unit, the analysis of the data using the adjustment program was then assessed. At the time of the 1999 Pandora expedition, the expedition team was eval- uating a program called Site Surveyor, a more advanced version of the Rule Web program. Up to that time HPASS had used Web, but we were aware of its limitations, particularly in handling large data sets. Previously, HPASS- Convert provided output in Web format, and these data were then adjusted using Web and the final results were presented in a text report or graphic DXF format. Peter Holt of 3H Consulting Ltd was approached seeking his assistance with the development of HPASSConvert so that it could be used
Depthin metres