GEOPHYSICAL SURVEY IN ARCHAEOLOGICAL FIELD EVALUATION Andrew David 1, Neil Linford 2, Paul Linford 3, 3 English Heritage Geophysics Team, Fort Cumberland, Eastney, Portsmouth PO4 9LD English Heritage V1.5, 60 Pages 2008 PEMD #383 2008 Geophysical Survey in Archaeological Field Evaluation Preface to the Second Edition exploitation, and integration with other imperative now that maritime archaeological These guidelines are intended to help prospecting disciplines. It is clear from our conservation is in the ascendant. archaeologists, particularly curators, consultants consultations that in these circumstances there and project managers, to better understand remains a need for independent guidance, The first edition of this guidance was published and engage with the techniques of geophysical which the following document is intended in 1995, and this revision is offered in the hope survey, for the best results. It is hoped too that to provide – not only for curators of the of maintaining a balanced and independent practitioners of geophysical survey will find archaeological resource, but also for others view on best practice in the context of progress them helpful and that, altogether, the guidance who need to know about the potential and since then.With the benefit of much positive can contribute to raising the consistency and pitfalls in more detail. Our purpose here advice, comment and discussion from many quality of geophysical survey in archaeological is above all dedicated to bettering the colleagues, for whose patience and advice we field evaluation. consistency and quality of geophysical survey are very thankful, we hope we have improved in evaluations, especially those arising from the content, and its presentation and clarity. Geophysical survey in archaeology continues development proposals. As the document is available on line to flourish. As of 2006, it is estimated to (http://www.english-heritage.org.uk/upload/ be a component of at least 23.4% of all Much of what was presented in the first edition pdf/GeophysicsGuidelines.pdf) we expect evaluations arising from planning applications remains valid and will be re-iterated here. to make future revisions and updates more (http://csweb.bournemouth.ac.uk/aip/aipintro.htm). There are, however, changes reflecting shifts immediately and easily in future and would, in thinking and approach that have taken place as ever, welcome comment and advice The techniques are also finding an increasing over the last few years.To take one example, towards these. role in the presentation and interpretation the debate on the efficacy of topsoil magnetic of archaeological sites, in contributing to susceptibility as an aid to evaluation, which was archaeological and forensic research, and very topical in the early 1990s, has moderated in helping to satisfy the demand for media now that it is increasingly accepted that detailed coverage of archaeological subjects. magnetometer coverage is preferable, and more feasible, over yet larger areas. More importantly, Geophysical survey has a wider academic and there have been changes in geophysical professional forum than was the case several instrumentation, technology, methodology and years ago. Since its inauguration in 1995 at software, all of which are having an impact on Bradford University in the UK there has the choice and performance of geophysical subsequently been a succession of biennial survey under varying conditions. A particular conferences on Archaeological Prospection, example is the great improvement in the virtues held in Japan, Germany, Austria, Poland, Italy of ground penetrating radar (GPR), now that and Slovakia, and attended by an ever more software and computing power enable both cosmopolitan variety of specialists in geophysics greater coverage and production of more and remote sensing.The Environmental and comprehensible display and interpretation. Industrial Geophysics Group (EIGG) of the Another significant development, following Geological Society has similarly hosted a the influential example of European practice, continuing series of biennial one-day meetings is the increasing awareness and availability of devoted to recent research in the subject.The alkali-vapour as well as fluxgate magnetometers. journal Archaeological Prospection, initiated in Both types of magnetometer, as well as other 1994, has gone on to establish itself as the main types of sensor, are now being deployed as vehicle for publication of relevant research and arrays on mobile platforms, with considerable case studies; and an International Society for potential to raise the versatility and speed Archaeological Prospection (ISAP) was initiated of ground coverage. in 2003 (http://www.archprospection.org). Archaeological geophysics is now a component Other areas of rapidly advancing progress of undergraduate teaching in at least 12 include the further integration of geophysical universities, although the only post-graduate data within Geographical Information Systems degree courses devoted to the subject are (GIS), which has in turn increased the need for the MSc in Archaeological Prospection at the consistency of data geo-referencing and archiving. University of Bradford (http://www.brad.ac.uk/ In parallel, there are a growing number of survey archsci/msc_ap.htm) and the MSc in projects that seek to integrate ground-based Archaeological Geophysics recently offered prospecting methods, together with remote at Orkney College of the University of the sensing technologies such as lidar, to maximise Highlands and Islands interpretative and analytical potential. (http://www.orkney.uhi.ac.uk/courses/archaeology/ geophysics-at-orkney-college-uhi). That said, wetlands, alluviated and urban environments persist as challenges to Despite the increasing familiarity with methods geophysicists. While not relevant here, but and techniques, and a growing number of to be the subject of future guidance from practitioners, geophysical survey can be both English Heritage (forthcoming 2008) it is a very technical subject, as well as a fertile worth noting that the remote examination area for continuing innovation, commercial of the shoreline and seabed is a growing 2 Contents Part I Standards for Geophysical Survey Preface to the Second Edition . 2 Part III Guide to Choice of Methods . 13 1 Introduction 1 Introduction . 13 There is currently no formalised standard for the conduct of geophysical survey in 2 Choice of geophysical survey . 13 Part I Standards for Geophysical Survey archaeological field evaluation. For the purpose 1 Introduction . 3 3 Costs . 14 of this guidance, however, it is expected that 4 Urban (and brownfield) sites . 14 such survey will, as far as is reasonably possible, 2 Guidance . 3 5 Cemeteries . 15 determine the nature of the detectable archaeological resource within a specified area 2.1 Justification for survey . 3 6 Alluvium . 16 using appropriate methods and practices1 . 7 Wetlands . 16 2.2 Fieldwork . 4 These will satisfy the stated aims of the 2.3 Data treatment . 4 8 Road and pipeline corridors . 17 survey project. Members of the Institute 2.4 Data interpretation . 4 9 Wind farms . 17 of Field Archaeologists (IFA) will, and other 2.5 The survey report . 4 10 Extremely large areas . 18 practitioners should, comply with the Code of conduct, Code of approved practice for 2.6 Dissemination . 5 the regulation of contractual arrangements in 2.7 Data archiving . 5 Part IV field archaeology, and other relevant by-laws 2.8 Competence of survey personnel . 5 Practitioner’s Guide to Good Practice of that Institution2. 1 Application of techniques . 19 1 Part II Geophysical Survey and Planning 1.1 The survey grid . 19 All relevant fieldwork must conform to the Standard and Guidance set out by the Institute 1 Archaeology and planning . 6 1.2 Magnetometer survey . 20 of Field Archaeologists for archaeological 1.3 Earth resistance field evaluation. 2 MoRPHE . 6 (resistivity) survey . 24 (http://www.archaeologists.net/modules/ 2.1 Start-up and planning . 6 1.4 Ground penetrating radar . 28 icontent/inPages/docs/codes/fldeval2001.pdf) 2 2.2 Execution . 6 1.5 Electromagnetic methods . 34 The IFA is the professional body for archaeologists in the United Kingdom 2.3 Closure . 7 1.6 Topsoil magnetic (www.archaeologists.net). It exists to advance susceptibility survey . .36 the practice of archaeology and allied disciplines 3 Briefs and specifications . 7 1.7 Other geophysical methods . 37 by promoting professional standards and ethics 3.1 The brief . 7 1.8 Metal detecting . 40 for conserving, managing, understanding and promoting enjoyment of heritage. It has about 3.2 The specification . 8 1.9 Geochemical methods . 40 2500 members in the UK and abroad. 1.10 Remote sensing . 41 4 The survey report . 9 This basic requirement for geophysical survey 4.1 Summary . 9 2 Analysis of geophysical data . 41 in archaeology is fairly straightforward, although 4.2 Introduction . 9 2.1 Data processing . 41 much will depend on the definition of what is ‘reasonably possible’.To help address this, 4.3 Methods . 9 2.2 Data display . 45 we initially itemise below some more precise 2.3 Data interpretation . 49 4.4 Results . 9 requirements that must be achieved; followed 4.5 Conclusions . 9 in Parts II–IV by more specific guidance on 4.6 Site location plan(s) . 9 References . 50 best practice. Part II (Geophysical Survey and 4.7 Data presentation – Glossary . 54 Planning) and Part III (Guide to the Choice of Methods) are aimed at those who commission plots and plans . 10 surveys; Part IV is a more in-depth description 4.8 Plots of raw data . 10 Appendix I Related standards, and assessment of the main methodologies, 4.9 Plots of processed data . 10 codes and guidance . 56 for those more concerned with these. 4.10 Interpretative diagrams . 10 Appendix II Contacts . 57 Appendix III Useful websites . 58 2 Guidance 2.1 Justification for survey 5 Dissemination . 10 Appendix IV List of consultees . 59 Prior to fieldwork, the geophysical survey 5.1 Sources of information . 10 requirements must be integrated within 5.2 Dissemination requirements . 11 Contributors . 60 a written statement (the project design, Acknowledgements .