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Monday, April 18, 2011

Monday Ground Up: The Role of Aerial Imagery in Archaeology

Guest article by John Carter

Long before Google Earth ever became a fixture on the Internet we’ve had aerial photos. In fact, the first aerial photo in the world was taken from a balloon of Boston Harbor in Massachusetts by James Wallace Black on October 13, 1860. There had been earlier attempts at aerial photography in Paris, France, but these were taken from a kite. From these humble beginnings, the use of aerial photography spread to many other disciplines including archaeology, but its main early use was in warfare. Extensive use was made of aerial photos taken from balloons during the American Civil War.

first aerial photograph used in archeology
(This is the first aerial photograph used in archeology. The site is Stonehenge in the United Kingdom. There have been many advances in aerial photography used in archeology since; one of them is Google Earth a powerful tool. This photo was taken by Lt. P.H. Sharpe from a balloon in 1906.)

The first aerial photos of an archaeology site were a set of photographs of both oblique and vertical taken by Lieutenant P.H. Sharpe in 1906 of the famous megaliths at Stonehenge. Between 1908 an 1911 a group of Italian engineers photographed the Forum Romanum along with the harbor works at Ostia. In 1912 a group of Italian archaeologists photographed a site that was thought to be a Roman fort from the air using a balloon. However later excavations proved this site was a Roman villa not a fort as first believed.

The first big improvement for aerial photos came about because of WWI.  World War I introduced the idea of dedicated aerial cameras to the field. During WWII further advancements in aerial photography were introduced including the use of color film. The growth of aerial photography touched off a revolution in the use of the full magnetic spectrum in what is now called “remote sensing.” If the whole magnetic spectrum were to run through a pipe it would have the diameter of the Earth, but the visible spectrum that we can see with our eyes would only have the diameter of a pencil. It is the unseen portions of the magnetic spectrum that are taken advantage of in remote sensing.

castle at Malden Hill, Somerset
(This is the castle at Malden Hill, Somerset an aerial photo of an Iron Age hill fort that was taken by the English Heritage Foundation. This is a good example of how aerial images are used in archeology.)

There are many uses for remote sensing across the broad spectrum of the disciplines that are used by mankind, archaeology being only one of them, but for the purposes of this paper we will only consider those that apply to archaeology within the visible spectrum, and specifically Google Earth and its close relatives.

Google Earth For DummiesA preliminary version of Google Earth was launched in April 2005 with Google Maps including satellite views, and Google Earth was finally launched as a free standing member of the Google family in June of the same year. There are similar products available from Teraserver and Flashearth and a whole collection of aerial imagery from the United States Geological Survey (USGS) that are all useful in archaeological studies.

Because of copyright constraints on Google Earth you must look up the sites on Google Earth yourself, but we will give you the geographic coordinates that appear at the bottom of the screen. This is one of the most useful of the many features of the program. As we understand these coordinates are accurate to 8 inches and can be used with a hand held Global Positioning device. Another useful feature of Google Earth is the ability to zoom in or out on your site of interest.

I recently wrote an article titled the First Mountain Railroad in the World  where I used Google Earth to trace the route of the Boston & Albany across the Berkshires from Chester to Pittsfield, Massachusetts allowing me to accurately trace the twists and turns of this railroad that was built in the 1840s. The coordinates for Chester, MA are: 42­­o 16’ 45.22” N 72o 58’ 43.18” W.

Great Pyramid of Chephren at Great Pyramids of Giza, Cairo, Egypt Photographic Poster Print by Cindy Miller Hopkins, 36x48Integrating Google Earth allows you to examine existing archaeological sites in full color like the Great Pyramids at Giza in Egypt. The Great Pyramid of Cheops can be seen at: 29o 58’ 33.74” N 31o 07’ 50.67” E that puts the cursor right at the pyramid’s pinnacle. By observing the shadows on the pyramid you can even determine the time of day the photo was taken. In this case the shadows indicate the exposure was made at about noon on the first day of summer. The shaded area is on the north face of the pyramid. The small blue squares are of the different photos of the site that have been uploaded. See if you can find the Sphinx in these aerial photographs, it is there.

Rome is an archaeologist’s paradise because there are so many archaeological treasures to be seen. Two of them are Capitoline Hill located at: 41o 53’ 34.22” N 12o 28’ 59.93 E and the Colosseum at: 51o 53’ 22.77 N 12o 29’ 30.29” W.

Google Earth has many features that are useful in archaeology along with other disciplines, the first of which is the ability to look down upon a site from above giving us the ability to see things that are not often seen from the ground. Among these many things are both present and future archaeological sites. Many of these sites are at present unknown, but by the use of aerial imagery they become apparent. There are many clues visible from the air causing these sites to stand out from the background. It is possible to make out the traces of old foundations or roads where future archaeological digs could take place. Some of the most obvious signs are stressed vegetation or sudden changes in the ground cover that are almost always sites requiring further examination.

It is not the purpose of this article to queue a full explanation of the things that are possible with Google Earth or photo interpretation, rather this article is intended to only act as an introduction to the subject. A great deal has been written on the subject already, and there are even associations that cover the discipline for those who are interested. One of these societies is the American Society of Photogrammetry and Remote Sensing (ASPRS),  where you can learn a great deal about the subject of not only aerial images, but also the field of remote sensing.

Author Bio

John Carter is a geologist that paid his way through college as a commercial helicopter pilot in the NY Metro area. He has had extensive experience as a prospector, and operated an environmental consulting firm specializing in environmental site assessments and is certified by the State of Connecticut as an Environmental Analyst III. In his early life he worked as an experimental machinist on aircraft and electronic parts before receiving his degree as a geologist.


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