Archaeological Applications

Visual image interpretation has proven particularly useful in locating sites whose exisence has been lost to history. Both surface and subsurface features of interest to archaeologists have been detected using visual image interpretation.

Surface features include visible ruins, mounds, rock piles, and various other markings. Examples of visible ruins are rock structures such as Stonehenge, castles, and Indian dwellings in serpent-shaped Indian mounds of the Midwestern U.S. Examples of rock structures are the various medicine wheels such as the Bighorn Medicine Wheel in Wyoming. Other surface markings include Indian pictographs and the ancient Nazca Lines in Peru.

Subsurface features include buried ruins of buildings ditches, canals, and roads. When such features are covered by agricultural fields or vegetation, they may be revealed on aerial or satelite images by tonal anomalies resulting from the subtle differences in soil moisture or crop growth. On occasion, such features have been revealed by ephemeral differences in frost patterns.

The spectrum of sunlight reflected by the Earth's surface contains information about the
composition of the surface, and it may reveal traces of past human activities, such as agriculture.
Since sand, cultivated soil, vegetation, and all kinds of rocks each have distinctive temperatures
and emit heat at different rates, sensors can "see" things beyond ordinary vision or cameras.
Differences in soil texture are revealed by fractional temperature variations. So it is possible to
identify loose soil that had been prehistoric agricultural fields, or was covering buried remains.
The Maya causeway was detected through emissions of infrared radiation at a different
wavelength from surrounding vegetation. More advanced versions of such multi-spectral scanners
(Visible & IR) can detect irrigation ditches filled with sediment because they hold more moisture
and thus have a temperature different from other soil. The ground above a buried stone wall, for
instance, may be a touch hotter than the surrounding terrain because the stone absorbs more
heat. Radar can penetrate darkness, cloud cover, thick jungle canopies, and even the ground.

Remote sensing can be a discovery technique, since the computer can be programmed to look
for distinctive "signatures" of energy emitted by a known site or feature in areas where surveys
have not been conducted. Such "signatures" serve as recognition features or fingerprints. Such
characteristics as elevation, distance from water, distance between sites or cities, corridors, and
transportation routes can help to predict the location of potential archeological sites.

Here is a list of the wavelengths that are best at detecting these differences (signitures), as well as additional useful information.

Here is more information on this diagram: http://www.ghcc.msfc.nasa.gov/archeology/remote_sensing.html

Interesting Links about the application of remote sensing to archaeology:

1) The Satellite Remote Sensing and Archaeology homepage: http://ourworld.compuserve.com/homepages/mjff/homepage.htm

2) Here is a story about how scientists have been "finding fossils from space" http://earthobservatory.nasa.gov/Study/Fossils/

3) Information concerning underwater archaeology: http://www.hamilton-scourge.city.hamilton.on.ca/remote.htm

4) This page details sources of imagery for use by the Satellite Archaeologist: http://ourworld.compuserve.com/homepages/mjff/sources.htm

5) An interactive map showing different areas of the world containing satellite images of archaeological features throughout the world. http://ourworld.compuserve.com/homepages/mjff/atlas.htm