Page 44 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 3
Search and Survey
I. INTRODUCTION
When I wrote the first edition of this book in 1989, much of the chapter on search and survey had not changed fundamentally for over 20 years. Surveys were regularly conducted with sounding sextants (a system that had changed little from the mid-19th century) with all the complexities and dif- ficulties of using these instruments. In most cases surveys were crude and the techniques were difficult to use. Who could have imagined, ten years later, that for a few hundred pounds one could have a hand-held instrument that could provide position, anywhere on the surface of the Earth, to a pre- cision of a few meters? The introduction of the Global Positioning System (GPS) in the 1980s was the start of this revolution. However, in the early days of GPS, with Selected Availability switched on, positions could only be obtained to an accuracy of ±50m. However, on May 1, 2000, NASA turned selective availability off and GPS was then able to give a position accurate to a few meters.
This chapter deals with methods of search and survey which require knowledge of position. Up until the availability of GPS, locating a position at sea was notoriously difficult. The first part of this chapter deals with posi- tion location and describes its largely redundant techniques and then con- centrates on the GPS system. It then goes on to describe the methods used to search and survey for sites (the actual survey of sites is dealt with in the Chapter 4). Most of the techniques described are used in other fields, par- ticularly the offshore oil industry. Although the equipment and resources that are generally used by maritime archaeologists are very modest in
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