Sunday, 29 November 2015

The Origin of Archaeological Geophysics

Archaeology owes a lot of its traditions and working methods to military developments (and some civillian applications) on both sides of the Atlantic. In particular, more modern methods of recording archaeology have been passed down as ex-military hardware and software. Geofizz has since become a mainstay in archaeology, made famous by Time Team and other TV programs. I will outline the developments of the principles of archaeological geophysics (or geofizz), while looking at the development of geofizz and the links to developments in other fields. Geophysics (the seperate geological subject) can trace its origins to the principles of magnetism to before Newton (see here); the Chinese invented the compass before 1000AD, knowing that it pointed towards the north pole because of the earth's magnetic properties, which they may have used to help circumnavigate the earth before Columbus (this is a very contentious issue! See here for more information).

Today I will look at the history of geophysics in archaeology and its development particularly in relation to the UK, although many other parts of the world have their own traditions in archaeologcial prospection.

See the end of the article for suggested reading! The suggested reading is also my bibliography.

The recorded history of Geophysics in Archaeology

It is tricky to mark the start of geofizz before World War 2. Pitt-Rivers arguably was the first person to record his geophysical efforts by using bowsing at Cranbourne Chase from the 1880's until the start of the 20th century. This involved slamming the flat end of a pick on the ground and listening to the change in tone. Some methods previously used include random and systematic shovel tests, trenching, soundings, probing and nose-sensitive dogsAugering is any method that makes sound travel through the ground and returns a response. As sound travels in waves, the frequency of the waves changes depending on the solids that are within the ground and reflect off different surfaces and different depths at varying frequencies (which will change the pitch and volume of the returning sound) . It's very simple- you can use a mallet and record the sound (in decibels or with a more subjective opinion) and then simply record where you hit the ground. Easy! Trouble is that augering is not very precise, and it hasn't been used by any serious archaeologists since at least World War 2. However it's a good way of explaining simple physical principles.

These approaches have been inaccurate, potentially destructive and not statistically representative, not to mention expensive. As a result many sites remained deeply buried or otherwise invisible and unstudied. A few rudimentary geophysical surveys that attempted to map buried cultural remains were carried out in Europe and America in the 1920's and 1930's,  using magnetic and resistance equipment that were developed for mining operations and often found geological anomalies rather than archaeological features but proved to be difficult to interpret.

A geophysical survey by Atkinson in 1946 at Dorchester-on-Thames is considered by many to be the starting point in modern archaeological geophysics. By using a wenner array, he could identify pits and ditches which were later verified by excavation. It was so successful (and ground-breaking, excuse the pun) that the results were published in French too. Others including Webster then went on to experiment with magnetic methods for investigating buried archaeological features in the 1950's and 1960's, most notably at Durobrivae near the A1 in the UK, where a Roman kiln was found with one of the first proton magnetometers developed for field use...

...But, the first accurately documented survey happened in Williamsberg, Virginia, where Mark Malamphy and Hans Lundberg used electromagnetic and inductive techniques from the 1920's onwards. Lundberg used an aeromagnetic survey from a hot air balloon in 1921 and may have completed the first electromagnetic survey from the air in the 1940's and he developed a vertical component magnetometer for use from a helicopter in the 1946. However, Malamphy gets the credit because Lundberg was involved in a car accident before the survey was due to take place.
By 1938 Marie Bauer Hall had set out a problem for the geophysicists at Williamsberg: a buried church that should have had a stone vault about 3 metres below the ground surface at the western end of the church. She engaged a geophysical company to investigate the site and the first technique they used was an "equipotential survey". By using grounded electrodes, a generator and a set of headphones (because the change in voltage was shown by changes in audio form an audio amplifier which was connected to two remote probes!). This was essentially a resistance survey! The survey was completed in 3rd November 1938 by Malamphy and an anomaly was found. Had they found the vault? Probably not; the anomaly was excavated and small fossil shells were found instead in a sandy sediment about 4 metres deep! Many other geophysicists carried out valuable early work but often went un-noticed because they were not based in the UK or US and hence rarely got published into English. Aktinson's work also had a far greater impact on archaeology and hence usually gets more credit.

Malamphy's results of the survey at Williamsburg. The lines in the top left are the direction of the electrical current in the ground based on a the acoustic response from the equipment.

The Start of Modern Archaeological Geophysics

During the 1950s modern archaeological geophysics began with crude but effective methods that could generate maps of buried sites, which piqued the interest of some archaeologists. Sometimes involved no more than a car battery a voltmeter and some wires and some were little more than sophisticated metal detectors! Nonetheless it paved the way for all future geophysics. Early collection was just data points on paper for later hand mapping. Some was recorded on magnetic tape for later digitisation, although this was exceptional. Sometimes field data, particularly radar, were printed on paper and could later be analysed for 3D, but this was time consuming and fraught with processing and interpretation problems. This was also very time consuming, limiting the areas that could be surveyed.
Relatively inexpensive computers in the 1980's helped increase the survey area hugely as data could be processed much more quickly by storing data in disks or on tape (in the field for the office later). The quality of the data was also improved as was the interpretations. Computer collection was quickly utilised by archaeological geophysicists and its expansion in the 1990's up to the present day.

Since Atkinson's surveys many institutes have been set up to study archaeological geophysics including MASCA in the USA and CRNS in France. One side effect was the influential journal Prospenzioni Archeologiche where many pioneering ideas and methods were tested, although many of the results were inconclusive, although this is down to the nature of the technology rather than the method itself. The UK had the Geophysics Section within the Ancient Monuments Laboratory, itself part of the Inspectorate of Ancient Monuments (now Historic England). The AM Lab was involved in the development of the fluxgate gradiometer, and they developed a way of continuously recording data for the first time. As a result this method dominated fluxgate surveys in the UK for 15 years from the 1970's, although coincidentally this coincided with a decline in advancement in archaeological geophysics globally. However many universities decided to teach geophysics as part of their curriculum by this point, starting with a postgraduate course at Bradford University in 1971 titled "Scientific Methods in Archaeology", followed by the undergraduate degree of Archaeological Sciences in 1975 and Bradford took over from Oxford as the leading UK archaeological geophysics centre, including developing the twin probe array for resistivity surveys, and creating software for the PC age in the 1980's, which is the mainstay for many resistance surveys today in the UK.

Today many countries have different ways of using geophyics within archaeology although many incorporate it into their archaeological strategy to identify features over a wide area. In the UK, the emphasis was on isolated sites until the late 1970's, when British Gas got the ball rolling by using geophysics in archaeological survey in a major pipeline survey across southern England as it would be buried in a known archaeologically sensitive area. Coinciding with this development was the introduction of more ubiquitous and cheaper technology, particularly GeoScan and Bartington equipment, which is still used today (albeit in improved forms). With instant data storage, less time was spent processing data, so the gratification of "instant results" was readily attainable. However, the sea-change came more completely with the change in legislation in the UK with the Planning Act and the introduction of PPG16, where the developer was made to pay for archaeological investigation in developments, leading to an unprecedented level of surveys. In 1980, barely 60 surveys were completed, mostly by the AM Lab. By 2003 over 250 surveys were completed, mostly by private firms for commercial puposes, although even today, as a guess, there are less than 500 people employed directly in archaeological geophysics, more likely closer to 250. Many amateur groups also have access to geophysical equipment. On a side note it has been argued that this legislation has made the archaeology merely a barrier to development, rather than a resource that can be used effectively to inform, entertain and educate the public, local groups and clients.

So while there are only a limited number of specialists today, geophysics in archaeology is considered an important part of the archaeologist's toolkit particularly in investigating and researching the landscape. There are many other areas of geophysics that are being explored today which I haven't touched on such as gravity for space, mineral and marine exploration among other fields. I've not even touched on the use of ground penetrating radar's contribution which has given us some amazing results! to give you an idea of a radar survey see the vidoe below. One day these other fields may provide archaeology with more mehods of searching for archaeology! However I could only find fleeting overlaps between geofizz and geophysics (excepting the geological principles), so perhaps my research hasn't been very thorough or archaeologists and geologists haven't spoken to each other enough! 

Suggested reading:

Bevan, B.W. 2000. An Early Geophysical Survey at Williamsburg, USA. Archaeological Prospection 7. Pp.51-58

Bevan, B.W and Kenyon 1975 MASCA Newsletter 11(2). Pp. 2-7, 

Conyers, L. B. 2013. Ground Penetrating Radar for Archaeology. Altamira Press, Plymouth. Pp.4-6

Conyers L.B, 1995 Geoarchaeology: An International Journal10 (4). Pp. 275-299

Gaffney, C and Gater. J. 2003. Revealing the Buried Past: Geophysics for Archaeologists. Tempus, Stroud. Pp.13-23

Van Leusen, 1998. Dowsing and Archaeology. Archaeological Prospection 5. Pp. 123-128

P.S. This is the second "tribute" post to Joe Raine!