Schlagwort-Archive: magnetometer

On the tracks of ancient cultures: Archaeological Geophysics

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As a team member of the first MUAFS season 2018/2019 responsible for magnetic investigations I would like to introduce the geophysical methods used for archaeological purposes. These methods will also be highly relevant for the DiverseNile project.

In the last decades, geophysics became a substantial part of archaeological projects. Depending on several factors, the most suitable geophysical method is chosen: the environment (desert, steppe, swampland etc.), the archaeological period and the used archaeological materials (stone, mudbrick etc.), but also the questioning (settlement layout and extension, cemetery detection etc.).  Additionally, the decision is influenced by available time, financial means and sometimes the season.

Still the fastest and most effective geophysical method in archaeology is magnetometry. It provides getting an overview of a site as well as its environment, extension and layout. Magnetic prospecting enables us to distinguish between settlement and burial sites, their structure, special buildings, open areas, as well as fortifications. Depending on the chosen sensors, we can learn more about the geology and environment and their changes over time. Accompanying measurements of magnetic susceptibility deliver information about magnetic properties of scattered objects and building materials as well as archaeological sediments and can be used in archaeological excavations as well.

Magnetic gradient investigations in Ginis 2019, site GiE 001 (Photo: Giulia D’Ercole).

But how does it work? Magnetometers are recording the intensity of the earth magnetic field with high-resolution. Nowadays, the earth magnetic field in the Attab to Ferka region has an intensity of around 39.400 Nanotesla (nT). With sensitive total field magnetometers, magnetic anomalies of less than 1 nT can be detected during archaeo-geophysical surveys, displaying even archaeological features like mudbrick walls or palisades.

Magnetic investigations benefit from varying magnetic properties of archaeological soils and sediments as well as materials. Every human activity regarding the surface is detectable because of different magnetic response. For example, digging a ditch, building a wall or using a kiln is changing or disturbing the actual earth magnetic field. What else can be detected? Architecture, streets, canals and riverbeds, ditches, pits and graves can be revealed just as palisades, posts and fire installations. Additionally, more information about geological and environmental conditions can be collected using magnetometry, e. g. paleo channels or former wadis.

For detecting stone architecture and for example voids, resistivity (areal or profile) and Ground Penetrating Radar (GPR) methods are applied, partly in addition to magnetic investigations. While magnetometry gives an overview about buried features beneath the surface in a ‘timeless picture’, GPR and ERT (Electrical Resistivity Tomography) provide more information about the depth and preserved height of the features. Of course, more than one geophysical method can be applied to get a comprehensive dataset for more complete interpretation of the results. Combined with archaeological work – survey and excavation – we can increase our knowledge and understanding of physical properties of archaeological and geological features as well as improve our interpretation.

Geophysical prospecting was originally developed for military purposes to detect submarine boats, aircrafts or gun emplacements. Furthermore, natural and especially mineral resources can be located. Geophysical methods and first of all magnetometry are used in archaeology since the late 1950s, when Martin Aitken detected Roman kilns in the UK. In Sudan, magnetometry is used since the late 1960s when Albert Hesse started investigations at Mirgissa in Lower Nubia. Since then, instruments as well as software programs for data collecting, processing and imaging have been developed and improved and offer detailed mapping of sites. First, geophysical prospecting can be applied fast, nondestructive and comprehensive. For magnetic prospection there is a variety of configurations to use, from handheld one/two-sensor instruments to motorized and multisensory systems but also different types of sensors. Through geographic information systems (GIS) geophysical investigations are benefiting from integrating high-resolution satellite images, drone images and models, survey and excavation data for a comprehensive interpretation of results.

After collecting magnetic data in the field, the files are downloaded and processed to get an idea of the first results. With that the field measurement proceeding can be adjusted as well as excavation trenches can be chosen. The detailed processing and analyzing of the collected field data are conducted back home on the desk.

References

Campana, Stefano; Piro, Salvatore (eds.) (2009): Seeing the Unseen. Geophysics and Landscape Archaeology. London: Taylor & Francis.

Dalan, R. (2017): Susceptiblity. In: Allan S. Gilbert, Paul Goldberg, Vance T. Holliday, Rolfe D. Mandel and Robert Siegmund Sternberg (eds.): Encyclopedia of Geoarchaeology. Dordrecht: Springer Reference (Encyclopedia of Earth Sciences Series), 939–944.

Fassbinder, Jörg W. E. (2017): Magnetometry for Archaeology. In: Allan S. Gilbert, Paul Goldberg, Vance T. Holliday, Rolfe D. Mandel and Robert Siegmund Sternberg (eds.): Encyclopedia of Geoarchaeology. Dordrecht: Springer Reference (Encyclopedia of Earth Sciences Series), 499–514.

Herbich, Tomasz (2019): Efficiency of the magnetic method in surveying desert sites in Egypt and Sudan: Case studies. In: Raffaele Persico, Salvatore Piro and Neil Linford (eds.): Innovation in Near-Surface Geophysics. Instrumentation, Application, and Data Processing Methods. First edition. Amsterdam, Oxford, Cambridge: Elsevier, 195–251.

Schmidt, Armin; Linford, Paul; Linford, Neil; David, Andrew; Gaffney, Chris; Sarris, Apostolos; Fassbinder, Jörg (2015): EAC Guidelines for the Use of Geophysics in Archaeology. Questions to Ask and Points to Consider. Namur: Europae Archaeologia Consilium (EAC Guidelines, 2).

Report on the test excavations of the 2020 season: GiE 001

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The world has changed since last week – COVID-19 has a major influence on archaeological fieldwork, universities and museums. MUAFS was very lucky in this respect – after our odyssey with the extra day in Khartoum and a night in Istanbul, we made it safely to Munich, just in time before borders got closed and flights cancelled. Of course all planned fieldwork in Egypt in April had to be cancelled and I could also not make my home visit to Vienna. But difficult times require flexibility and the most important thing now is of course to flatten the curve and to stay safe (and home)!

Well – research for MUAFS is of course still possible and all of us are using the time in home office for reading things and compiling the data from the 2020 season.

The following is just a short summary of our test excavations of the 2020 season – this season was a preparation season for the next, longer field season which will be the start of my new European Research Council Project DiverseNile. Thus, the focus was on promising sites dating to the Bronze Age/Kerma Period in the Ginis East area where also Egyptian presence of the New Kingdom is attested.

In order to get familiar with the site formation processes and sedimentation in the area, we conducted at four sites in the district of Ginis East small test excavations. A total of 8 trenches were excavated by the team; local workmen will be engaged in the next season.

Location of sites and test trenches at Ginis East 2020.

As you will see in the following – the results from the individual sites were not as we hoped for but are nevertheless very important outcomes of what was designed as a test season.

I will start with site GIE 001 and a separate post will present the results from the other sites at Ginis East.

GiE 001 – a New Kingdom (and Kerma?) settlement site

Recorded by Vila as 2-T-36B, this domestic site at Ginis East can be assigned to the Egyptian New Kingdom, showing also an intriguing Kerma presence according to the surface finds. Magnetometry was conducted by MUAFS in 2019. In the 2020 season, two trenches were laid out above promising anomalies in the magnetometry in the northeastern part of the site.

Trench 1 (6 x 4 m) yielded, apart from surface finds which were mixed and dated from the Kerma Period, the New Kingdom, the Napatan Period and Christian times, some Kerma Classique sherds from lower levels. However, no structures were found and the magnetometry seems to show natural features, especially more sandy areas which contrast to clay layers/alluvial sediments.

Trench 2 (10 x 4 m) generated large quantities of ceramics and stone tools from the surface. The main archaeological features found in this trench were sub-recent pits deriving from marog activities. The largest of these pits in Trench 2, Feature 1, is 2.40 m in diameter and 75 cm deep. It was filled with fine sand and the traces of the tools the marog diggers used are clearly visible on the sloping edges. We documented everything in 3D according to our standard procedure. The find material comprised mostly mixed pottery from the New Kingdom, Napatan and Medieval era as well as some recent date seeds and small pieces of charcoal and bone.

Feature 1, the marog pit, in Trench 2 at GIE 001.

Both trenches in GiE 001 did not yield mud bricks or any structures from the New Kingdom; it is likely that this part with the trenches is already located outside of the former settlement area. That the area was inhabited and used during both the 18th Dynasty and the Ramesside period, becomes nevertheless evident from the find assemblages we collected.

Excavation and processing of data at GIE 001 will continue, but for now the New Kingdom site with later use seems associated with gold exploitation in the periphery of Sai Island and Amara West, as I have already proposed in an earlier post based on the finds (ceramics and stone tools).

Summary of week 3 at Ginis East

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Our third week of the 2020 just ended and was very successful. We concentrated during the week on site GiE 001. Recorded by Vila as site 2-T-36B in the 1970s, this domestic site at Ginis East can be assigned to the Egyptian New Kingdom, showing also an intriguing Kerma presence according to the surface finds as well as Napatan ceramics. Magnetometry was conducted by MUAFS in 2019.

In the 2020 season, two trenches were laid out above promising anomalies in the magnetometry in the northeastern part of the site, just south of the modern car track. Trench 1 (6 x 4 m) yielded, apart from surface finds which were mixed and dated from the Kerma Period, the New Kingdom, the Napatan Period and Christian times, some Kerma Classique sherds from lower levels. However, no structures were found and the magnetometry seems to show natural features, especially more sandy areas which contrast to clay layers.

Trench 2 (10 x 4 m) is the area where we found plenty of evidence for marog digging. The pottery was abundant and is again a mix of predominantly New Kingdom material with Kerma, Napatan and Christian wares. Work in Trench 2 is not yet finished and will continue in the upcoming week.

All in all, remains in GiE 001 are clearly not as we were hoping according to the magnetometry, but it is still a very interesting site to study, especially within the context of the question of Egyptian presence during the New Kingdom in the area of Attab/Ginis/Kosha, thus in the periphery of Amara West and Sai Island.