The Application

Of

Remote Sensing Technology

As it Applies to

The Field of Archeology

by

Mike Dixon

FORESTRY 4217

REMOTE SENSING TERM PAPER

The Application

Of

Remote Sensing Technology

As it Applies to

The Field of Archeology

By

Mike Dixon

An Undergraduate Term Paper Submitted

In Partial Fulfillment of the Requirements for

The Degree of Honours Bachelor of Science in Forestry

Faculty of Forestry and the Forest Environment

Lakehead University

April, 2003

CONTENTS

PAGE

List of Figures (I)

INTRODUCTION 1

DISCUSION 2 History of Remote Sensing and Archeology 2 APPLICATIONS OF TECHNOLOGY 3 Crop Circles, A Plausible Explanation 3 Landsat Thematic Mapper 4 Radar, the Next Big Breakthrough 6 Ground Penetrating Radar 10

CONCLUSION 12

Literature Cited 13

List of Figures

Page

Figure 1. Landsat image of Roman Villa 4 Figure 2. Landsat Image of the “Roads to Ubar” 5 Figure 3. SIR-C Image of Angkor, Cambodia. 9 Figure 4. Ground Penetrating Radar Unit. 10 Figure 5. Discovery Trenches. 11

INTRODUCTION

Remote sensing began with the use of aerial photography and is acknowledged

as a valuable tool for viewing, analyzing, characterizing, and making decisions about our

environment. In the past few decades, remote sensing technology has advanced on three

fronts: 1) From a predominantly military uses to a variety of environmental analysis

applications that relate to land, ocean, and atmosphere issues; 2) From photographic

systems to sensors that convert energy from many parts of the electromagnetic spectrum

to electronic signals; and 3) From aircraft to satellite platforms.

Today, we define satellite remote sensing as the use of satellite-borne sensors to

observe, measure, and record the electromagnetic radiation reflected or emitted by the

Earth and its environment for subsequent analysis and extraction of information.

The basic principles of remote sensing are derived from the characteristics and

interactions of electromagnetic radiation (EMR) between sources to the sensor. The

principles are as follows: 1) The source of energy and the type and amount of energy it

provides; 2) The absorption and scattering effects of the atmosphere on EMR; 3) The

mechanisms of EMR interaction with Earth surface features; and 4) the nature of sensor

response as determined by the type of sensor.

Archeology is the art and science of the study of past human life and activities

through the remains of the culture of a people. It is, for the most part, a “low tech”

discipline, that relies on historical accounts, legends and supposition to locate areas of

interest. Many artifacts are hidden through time by the normal environmental processes

such as vegetation growth or through catastrophic events such as earthquakes or

volcanic eruptions. Labour intensive efforts are required to unearth these hidden

mysteries of the past once their location has been estimated. This is a costly venture that

frequently produces unsatisfactory results.

It is the intention of this paper to explore the application of various tools of the

remote sensing technology as they pertain to the field of archeology and to determine if

remote sensing is a suitable tool for locating archeological sites.

DISCUSION

History of Remote Sensing and Archeology

It can be argued that the greatest advancement in archaeology since the shovel is

remote sensing. To be able to determine an archaeological site before actually digging it

out saves time and money allowing the archeologist to concentrate efforts in likely areas

without wasting resources (Anon,2003). This type of determination can take place either

from a sensor platform orbiting the earth, from on board an aircraft or through ground

efforts with sophisticated devices.

The first known aerial photographs of an archaeological site were taken from a

war balloon in the early 1900s over England. The target was Stonehenge. In World War

I, photographers conducting military reconnaissance flights observed sites of

archaeological interest that were not visible from ground level observation points. These

aerial observation benefits soon became useful tool used for the discovery of until then,

unknown archeological sites (Anon,2003).

Aerial platforms for remote sensing are limited by two significant drawbacks, a

finite ceiling of flight and the ability of the human eye to see only so much detail in a

photograph. It was not until the launch of multi-spectral imaging platforms that orbit the

earth that the appreciation of remote sensing was fully realized by archeologists

however. Multi-spectral data that has been classified and enhanced by various computer

programs has returned images of the earth that was not imagined possible by the early

pioneers of archeology.

The field of remote sensing in archeology is not the final solution to finding new

“digs”, but must be used with common sense in conjunction with historical accounts of

events and legends. The location of various sites can be pin-pointed using various

imaging methods but you still must now the general area in which to look. There is little

likelihood of finding a Roman Legion fort on the Black Bay Peninsula for instance, but

likelihood increases when images of various regions of Europe are examined where the

activities of the Roman Empire were known to occur.

APPLICATIONS OF TECHNOLOGY

Crop Circles, A Plausible Explanation

Although Mel Gibson has recently released a version of the origin of crop

circles, a more likely explanation can be found through remote sensing and archeology.

When aerial observations of previously undiscovered archeological sites were

first discovered, they were detected by the presence of crop circles or patterns found in

observed farmers fields. These patterns were displayed as either lighter of darker in

colour than the vegetation on either side. Crop circles observed were buried structure

under the crops that effected the vegetation in some way. These circles could either be

“positive” as in holding soil moisture longer than the surrounding soil, or, “negative” as

in deflecting moisture away from the vegetation directly overtop the structure. Figure 1,

depicts a buried Roman villa found in Burgundy, France that has been imaged using

Landsat thematic mapper and enhanced.

.

Figure 1. Landsat image of Roman Villa Source: http://www.geo-informatie.nl Landsat, Thematic Mapper

One of the more common remote sensing platforms used for image analysis and

archeology is the Landsat series 4 and 5 satellites that are equipped with “thematic

mapper”. The space-bourn thematic mapper (TM) is capable of returning seven channels

of digital data back to a receiver on earth, three in the red, green, blue visible spectrum,

three in the reflective infrared (IR) spectrum, and one in the thermal IR spectrum. These

“multi-spectral” images are processed and enhanced by various computer programs to

bring out features that are not discernable to the human eye. An example of this feature

can be found below in Figure 1. Landsat was able to detect variations in the topography

of the image that led archeologists to the mythical lost city of Ubar located in Oman.

Ubar was a fortress across the city that existed from 2500 BC to around 300AD and

serviced the incense trade that crossed the Rub al Khali desert or, the “empty quarter” of

southern Arabia.

Several previous expeditions had previously attempted to find Ubar starting with

Bertram Thomas who found evidence of a caravan route across the desert some 60+

years ago. Thomas found shards of pottery along the route and a local Bedouin guide

called it "the road to Ubar", but Thomas was turned back by the inhospitable conditions

of the desert itself after mapping the location of the caravan route. Another expedition

headed by an archaeologist named Wendell Phillips attempted to find Ubar in the 1950s

using trucks and camels to cross the desert. Phillips was successful in finding Thomas’s

caravan route but the desert sand dunes prevented him from finding the city itself.

It was the Gulf War of 1991 that provided images of the region to an amateur

archeologist named Nicholas Clapp who had been on previous expeditions to find Ubar

unsuccessfully. These images from Landsat showed a series of roads in the desert that

pointed to a location near the village of Shisur. After investigating the scene with ground

penetrating radar ( to be discussed further on) and excavating walls and pillars, the lost

city of Ubar was rediscovered.

Figure 2. Landsat Image of the “Roads to Ubar” Source: http://www.pbs.org

Biblical accounts, and those found in the Koran, described the demise of Ubar as

a result of God’s displeasure with the city’s inhabitants. The wrath of God caused the

city to be destroyed overnight leaving only the desert to remain. Excavations on site

revealed that the walls of the fortress had been constructed over an immense limestone

cavern that had collapsed - burying the city beneath the sands. Not only was the city

found where historical accounts had recorded it’s location but, the destruction of the city

was reasonably explained and accurate (Conyers,2003).

Clearly, finding the lost city would likely never have occurred without the use of

remote sensing and common sense interpretation of the legends surrounding the

location.

Radar, the Next Big Breakthrough

Radar (RAdio Detection and Ranging), simply measures the strength and round-

trip time of the microwave signals that are emitted by a radar antenna and reflected off a

distant reflecting surface or object (Freeman,2003). The unit alternately transmits and

receives pulses at particular microwave wavelengths (in the frequency range of 300

MHz to 30 GHz).

For an imaging radar system, about 1500 high- power pulses per second are

transmitted toward the target or imaging area.. At the Earth's surface, the energy in the

radar pulse is scattered in all directions, with some reflected back toward the antenna,

known as back splatter. Backscatter, or echoes return to the radar as a weaker radar echo

and is received by the antenna. These echoes are converted to digital data and passed to

a data recorder for later processing and display as an image. A radar pulse travels at the

speed of light and the roundtrip time is measured to calculate range to the reflecting

object (Freeman,2003).

So, how is radar used in archeology? Various sensor platforms have been

launched with radar units on board. One such unit is the SIR-C unit that was on board

shuttle launches during the early 1990’s. Built by the Jet Propulsion Laboratory (JPL)

and the Ball Communication System Division for NASA, SIR-C uses radar imagery to

make measurements of: Vegetation type, extent and deforestation; Soil moisture content;

Ocean dynamics, wave and surface wind speeds and directions; Volcanism and tectonic

activity; Soil erosion and desertification.

Space borne radar is a capable of penetrating vegetation, ice, and soil and is

particularly useful in penetrating dry soils such as found in desert conditions(Freeman,

2003). As an application for archeology, radar is able to look beneath visible surface

details to see hidden structure underneath. Figure 2 details the city of Angkor in

Cambodia, Angkor was a vast complex of more than 60 temples dating back to the 9th

century that served as the spiritual center for the Khmer people(Anon, 2003). At its

pinnacle, the city housed a population of about 1 million people and was supported by a

massive hydrological system of reservoirs and canals. Angkor existed for approximately

800 years and gradually was abandoned over time. As the rainforest encroached over

time, details such as irrigation canals, lesser temples and courtyards were lost

underneath. Archeologists studying this image believe the blue-purple area slightly

north of Angkor may be previously undiscovered structures (Anon,2003). In the lower

right is a bright rectangle surrounded by a dark reservoir, which houses the temple

complex Chau Srei Vibol. The colors in this image were obtained using the following

radar channels: red represents the L-band (horizontally transmitted and received); green

represents the L-band (horizontally transmitted and vertically received); blue represents

the C-band (horizontally transmitted and vertically received)(Anon,2003). The urban

area at the lower left of the image is the present-day town of Siem Reap. The adjoining

lines are both modern and ancient roads and the remains of Angkor's vast canal system

that was used for both irrigation and transportation. The large black rectangles are

ancient reservoirs(Anon,2003).

Figure 3. SIR-C Image of Angkor, Cambodia. Source: http://www.jpl.nasa.gov

Ground Penetrating Radar

As powerful a tool to archeology that space borne radar is, it is limited by

various soil characteristics such as mineral content, water and vegetation and image

availability to the archeologist. Another radar unit available and more accessible to the

archeologist is the ground penetrating radar (GPR) unit that may be suspended from an

aircraft or simply dragged along the ground (Figure 4). GPR works in much the same

way as space borne radar does but is able to be directed more precisely.

.

Figure 4. Ground Penetrating Radar Unit. Source: http://www.du.edu

Investigations of suspected sites in the past would have the archeologist start the

investigation by digging a series of orderly trenches either by hand or by machinery

(Figure 5). This method established the perimeter of the dig but could often be

somewhat destructive to artifacts buried beneath the surface. Another problem would be

that many times a village site or campground etc. had been built over top of other

structures and the potential to miss these other structures would be significant (Conyers,

2003).

Figure 5. Discovery Trenches. Source: http://www.du.edu GPR has the ability, under the right circumstances to be able to identify

structures layered over top of one another without destructive sampling Conyers, 2003).

Transferred directly to a portable computer, the GPR image is processed and enhanced

providing valuable information about what lies beneath before the first shovel of dirt is

moved. This remote sensing application saves time and money when used by taking the

guess work out of where to dig fist, and how deep to dig.

CONCLUSION

The field of remote sensing obviously has more potential than that of resource

management uses previously explored in the 4217 elective. The ability to access imagery

that has been archived can reduce the overhead cost and analysis methods would be

similar to what has been experienced so far. Archeology and the use of remote sensing

would appear to be a logical combination of lower resolution images such as Landsat to

identify potential areas with higher resolution images such as found with IKONOS to

narrow done the field of interest. Radar imagery can isolate hidden features and subtle

changes in topography to further identify potential archeological sites of interest. All of

this can be done at a considerable lower cost than traditional methods enabling more

funds to be allocated to the actual dig than to the exploration for hidden sites.

The most important tool to the archeologist may be the shovel and common

sense but remote sensing technology places a traditionally low tech science associated

with digging in the dirt, jungles, deserts and harsh living conditions, into the realm of

space age intelligence gathering.

Literature Cited

Anonymous, 2003. Archeological Remote Sensing. http://gncc.msfc.nasa.gov/archeology/remote_sensing.html. 03/28/03

Anonymous, 2003. The Sky’s Eyes: Remote Sensing in Archeology. NOVA Online.

http://www.pbs.org/wgbh/nova/ubar/tools/ 03/28/03 Conyers, L. 2003. GPR in Archeology: Using radar geophysics to locate and map

buried archaeological features. http://www.du.edu/~lconyer/. 03/28/03 Freeman, T. 2003. What is Imaging Radar? Http://southport,jpl.nasa.gov/ 03/28/03 Pinson, L.C. S. Newby. 2003. Remote Sensing Equipment.

http:www.archeologyinc.org/hightec.html. 03/28/03