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Archaeological Survey Methods Mosul University Archaeology Program 1 Overview • Archaeological survey methods allow for a regional, diachronic study of past human activity • The analysis of surface artifacts and features provides a great deal of information • Aerial photographs and satellite imagery can help identify and locate archaeological features in a large area • Geophysical methods can locate subsurface archaeological features • A geographic information system can provide can organize and analyze all these data in an accessible manner 2 Objectives • In this lecture, you will learn the following elements of archaeological method and theory: – Pedestrian survey – Mapping – Geographic information systems – Remote sensing techniques – Geophysical survey methods 3 Key Terms • • • • • Sampling strategy Intensive versus extensive pedestrian survey Geographic information system Remote sensing Electromagnetic spectrum Photo: Author’s own 4 Archaeological Survey • Locate, measure, map, and quantify archaeological features and materials over broad area • Purpose is to understand regional patterns and long-term change • Combines multiple techniques Photo: Author’s own 5 Research Questions • Human-environment interaction – Seasonality, agriculture, animal husbandry, geomorphology, landscape degradation – How people experienced their surroundings • Settlement patterns – Hierarchy, infrastructure, resource management • Networks: political, social, economic – Trade, pilgrimage, communication • Change over time 6 6 Survey versus Excavation • Benefits: – Non-destructive – Faster data processing time – Lower financial investment – Less personnel – Easier permit process (usually) • Hindrances: - Some methods require specialized software, equipment, or personnel at an extra cost - Results can vary with each season - Ground-truthing may be needed 7 7 Pedestrian Survey • Locates, describes, quantifies archaeological materials found on the surface of a specific area • Unsystematic vs. systematic Photo: AROURA Project 2011 8 8 Reconnaissance • Uses textual sources, maps, photography • Scout, locate, map prominent archaeological features surface • Unsystematic and opportunistic • Results are biased Photo: Author’s own Photo: Author’s own Photo: Author’s own 9 9 Unsystematic Survey • Visually scan the surface • Record information • No sampling strategy • Usually in conjunction with reconnaissance • Results considered inherently biased Photo: A Smith 10 10 Systematic Survey • Survey boundaries defined • Area is divided into sectors • Sampled in grid or traverse system Photo: AROURA Project 2010 Photo: AROURA Project 2011 11 11 Traverse and Grid TRAVERSE X X X X X X X X X X X X X X X X GRID 12 12 Survey Design • Study history of cultural and natural events • Boundaries • Scope – Intensive – Extensive Photo: AROURA Project Photo: AROURA Project Photo: Author’s own • Collection strategy Photo: Author’s own 13 13 Extensive Survey • Study of large area or multiple regions • Low coverage • Narrow sampling strategy • Random sampling Image: AROURA Project 14 14 Intensive survey • Small area, typically one site • High to total coverage • Stratified and selective sampling • Perfect total coverage usually impossible Image: AROURA Project 15 15 Sampling Strategy • • • • Stratified Random Stratified Selective Goal is to avoid bias in data Random 16 16 Collection Management • Determine how material will be processed, collected, and stored • Collect or field process? • Processing and storage space? Photo: Author’s own Photo: Author’s own Photo: AROURA Project 2012 17 17 Documentation • • • • • • • • Location Visibility Slope and terrain Materials collected Sediment Weather Time of day ID of surveyor Photos: Author’s own 18 18 Archaeological Mapping • Scale: – Region – Site – Feature • Precision vs. Accuracy Image: AROURA Project 19 Image: AROURA Project 19 Mapping: Manual • Equipment: – Compass – Measuring tape • Best for mapping small areas/ features, laying survey grids • Accuracy dependent on terrain, slope, user Photo: MF Lane 2011 Photo: Author’s own 20 20 Mapping: Digital • Equipment – Laser survey equipment – Satellite-based locational system • Best for covering large areas • Equipment very precise, occasionally to a fault Photo: Author’s own Photo: AROURA Project 2010 21 21 Geographic Information System • Designed for the collection, storage, retrieval, analysis, and display of data • Can combine multiple types of data • Not just for making maps! Image: AROURA Project 22 22 GIS Image: AROURA Project Image: AROURA Project 23 23 GIS Data Components • Combines both locational and attribute date • Vector – Points – Lines – Polygons • Raster Point -2 -1 0 1 Line 2 Polygon -1 0 0 0 1 0 0 0 1 2 0 0 1 2 3 1 1 2 2 3 Raster 24 24 Spatial Analysis • Use computational algorithms to carry out statistical analysis • Can create new information • Only as valuable as the data used Image: WikiCommons 25 25 Remote Sensing • Ground based: – Geophysical prospection • Low altitude: Image: AROURA Project – Aerial photography – LiDAR Image: AROURA Project • High Altitude: Image: WikiCommons – Multispectral satellite imagery – SRTM 26 Image: WikiCommons 26 Satellite Imagery • Higher the spatial resolution, the lower the spectral resolution (vice versa) • Types of satellites: – LANDSAT – GeoEye – DigitalGlobe Image: WikiCommons 27 27 Electromagnetic Spectrum • Frequencies of radiation • Characteristics: – Wavelength – Frequency (Hz) – Wavelength is inversely proportional to frequency – Visible spectrum = what humans can see Image: WikiCommons 28 28 Imagery Distortion • Results can vary seasonally • Refraction and reflection • Resolution – Spatial: IFOV – Spectral – Temporal Image: WikiCommons 29 29 Crop Marks • Subsurface features can efect vegetation health • Structures hinder growth • Ditches can encourage growth Image: WikiCommons Image: WikiCommons 30 30 Surface Features • Some features are so large they are impossible to comprehend at ground level • Imagery can be used to understand spatial layout Image: WikiCommons Image: WikiCommons 31 31 Multispectral Satellite Imagery • Satellite sensors measure EM spectrum • Requires processing software • Sensors: True Color – 3 visual spectrum – Infrared – Thermal infrared False Color 32 Image: WikiCommons 32 Processing Multispectral Imagery • Can combine multiple bands to produce true and false color images • Can classify spectral data to identify anomalies Photo: AROURA Project 33 33 Digital Elevation Model • 3D representation of Earth’s surface • SRTM – Radar antennae mounted to space shuttle – Global coverage – low spatial resolution • LiDAR – can be attached to plane, helicopter, even tripod – Local coverage – Higher spatial resolution Image: WikiCommons Image: WikiCommons 34 34 Aerial Photography • Image sensors mounted to plane • Great deal of declassified military data available • Targeted photos can be expensive Photo: AROURA Project 35 35 Balloon/Kite Photography • Inexpensive • Does not require exclusive equipment or personnel • Can specifically target desired features • Oblique and vertical angles • Must take care in high winds, trees, power lines Photo: Author’s own 36 36 Geophysical Methods • Active: emits and • Important factors: - Nature of archaeological receives signal • Passive: takes measurements features - Sediment composition - Size of survey area - Surrounding modern elements - Time of day - Collection speed 37 37 Magnetometry • Method: passive – Measures small changes in magnetic field of archaeological features – Must calibrate against Earth’s magnetic field – Does not require surface contact • Bad for: built structures (unless made of fired brick or magnetic soil) • Good: ditches, pits, burnt features Photo: Author’s own Image: AROURA Project 38 38 Electromagnetic Susceptibility • Method: Active – Transmits & receives EM wave – Measures both magnetic susceptibility – Does not require surface contact Image: WikiCommons • Can detect a variety of built and in-filled features • Performs well in dry climates 39 39 Resistivity • Method: Active – Sends electric current into ground – Resistance to flow is measured – Requires surface contact • Can detect a variety of built and in-filled features • Results can vary with soil moisture Photo: M Staudter 40 40 Ground Penetrating Radar (GPR) Photo: T. Parno • Method: Active – Transmits radio pulse into ground, measures amount of time for signal to reflect back to antenna – Can provide 3D view of subsurface: “time-slices” – Requires surface contact • Good for: stone and brick • Bad for: soils with high conductivity (wet or finegrained sediments) Photo: C. Dayton 41 41 Lesser Used Methods • Microgravity • Seismology • Metal detecting Image: WikiCommons 42 Conclusions • Archaeological survey studies past human activity across space and time • Multi-scalar temporal and spatial approach best achieved using multiple methods • The study of ephemeral surface features and artifact scatters require a systematic approach to collection, analysis, and interpretation • Ground-based, high- and low-altitude remote sensing can identify subsurface features • Not a means to an end (excavation) 43 Further Reading • G.G. White and T.F. King (2007) Archaeological Survey Manual. Left Coast Press: Walnut Creek, CAs. • E.B. Banning (2003). Archaeological Survey. Springer: London. • P. Howard (2007) Archaeological Surveying and Mapping: Recording and Depicting the Landscape. London: Routledge. • H. Chapman (2007). Landscape Archaeology and GIS. London: Tempus. • D.C. Comer and M.J. Harrower (2013). Mapping Archaeological Landscapes from Space. Springer: London. • R. Lasaponara and N. Masini (2012) Satellite Remote Sensing: A new Tool For Archaeology. London: Springer. • J. Gater and C. Gaffney (2003) Revealing the Buried Past: Geophysics for Archaeologists. London: Tempus Press. 44 44