Page 156 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 4: Conventional Survey 135
Figure 4.19 HPASS diver unit. Operator on left is holding the mobile recording transpon- der. (Courtesy of Gary Cranitch, Queensland Museum.)
°C), depth (in meters), and the six transponder-to-diver-unit distances (in meters). Associated with each of these measurements (excluding time) was the standard deviation of the measurement and the number of measurements used to obtain the final value (the unit usually made 20 measurements to each transponder and the program rejected readings that lay outside a predetermined range). In studying the resulting data, it was found that there were a number of interesting factors that affected the results.
2. Temperature Considerations
The Pandora site lies on the edge of the continental shelf in a region where there are numerous reef and lagoon areas. With the tidal range, the water is noticeably variable in the current strength and temperature, sug- gesting that water from the warm lagoon areas and the colder deep ocean was ebbing and flowing in an unpredictable manner through the site. Read- ings showed a remarkable variation in temperature, varying between 24.3 and 28.8°C over the period of the expedition and by up to 0.6°C over the course of a dive (Figure 4.20). These variations suggested that using the