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June 2004 |
Geomatics in archaeology High tech for old digs
The new ultra-high (less than 1 meter) spatial resolution satellite systems are now providing archaeologists what they have long desired: the ability to actually locate the faint vestiges of ancient landscapes from space around the world (Fowler, 1996), although cost is always a real problem for archaeologists. There are several examples of new sites, road networks, and other archaeological remains having been located on these new space images.
Another important type of remote sensing for archaeology is geophysical remote sensing. Once we locate a site on aerial imagery of through field survey, we need to know how and where to excavate it, or if it is worth excavation at all. Ground remote sensing tools such as ground penetrating radar, resistivity, and magnetometry allow us to create non-destructive images of features below the ground. These tools, especially when used together, can provide important information of the depth and content of buried features. New digital systems produce data that can be directly entered into the GIS environment for analysis and comparison with aerial imagery and other GIS data.

Silk Route, China (SIR-C/X-SAR C, L bands)
This composite image is of an area thought to contain the ruins of the ancient settlement of Niya. It is located in the southwest corner of the Taklamakan Desert in China's Sinjiang Province. This region was part of some of China's earliest dynasties and from the third century BC on was traversed by the famous Silk Road. The Silk Road, passing east-west through this image, was an ancient trade route that led across Central Asia's desert to Persia, Byzantium and Rome. The multi-frequency, multi-polarized radar imagery was acquired on orbit 106 of the space shuttle Endeavour on April 16, 1994 by the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR). The image is centered at 37.78 degrees north latitude and 82.41 degrees east longitude. The area shown is approximately 35 kilometers by 83 kilometers (22 miles by 51 miles). The image is a composite of an image from an Earth-orbiting satellite called Systeme Probatoire d'Observation de la Terre (SPOT) and a SIR-C multi-frequency, multi-polarized radar image. The false-color radar image was created by displaying the C-band (horizontally transmitted and received) return in red, the L-band (horizontally transmitted and received) return in green, and the L-band (horizontally transmitted and vertically received) return in blue. The prominent east/west pink formation at the bottom of the image is most likely a ridge of loosely consolidated sedimentary rock. The Niya River -- the black feature in the lower right of the French satellite image - meanders north-northeast until it clears the sedimentary ridge, at which point it abruptly turns northwest. Sediment and evaporite deposits left by the river over millennia dominate the center and upper right of the radar image (in light pink). High ground, ridges and dunes are seen among the riverbed meanderings as mottled blue. Through image enhancement and analysis, a new feature probably representing a man-made canal has been discovered and mapped.
Image courtesy of NASA Jet Propulsion Laboratory (Pasadena)
Global positioning System
One of our traditional problems while doing field surveys was to determine our accurate location. GPS has revolutionized field survey methods by allowing archaeologists to easily and accurately locate our position and to record on a data logger (and digital camera) what we find in the field. All of these are then entered into the GIS environment for further analysis. Another frequent use of GPS in the field is to download coordinates and navigate ourselves to a particular location on a featureless plain or vast forest zone. We do this when we find an interesting feature on an aerial or satellite image, or develop a GIS based predictive model of site locations, and want to go to that specific point on the ground. At the very least, we spend a lot less time being lost in the field! Site excavations now routinely rely on laser theodolites, tied into a GPS network, for precise mapping of excavation features and to 'tie in' the excavation data with the rest of the GIS database.
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