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Remote Sensing Technologies
Bible Research Applications
Remote sensing and Geographic Information Systems (GIS) offer great advantages for archaeological related research. The following provide brief descriptions of these technologies and their use in this field.
GIS
A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on our planet. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies. GIS provides the power to create, map, integrate information, visualize scenarios, solve complicated problems, and develop effective solutions like never before. GIS is a tool used by individuals and organizations, schools, governments, and businesses seeking innovative ways to solve their problems.
Example of a GIS display of Terrain Data
Mapmaking and geographic analysis are not new, but a GIS performs these tasks better and faster than do the old manual methods. Before GIS technology, only a few people had the skills necessary to use geographic information to help with decision making and problem solving.
Today, GIS is a multibillion-dollar industry employing hundreds of thousands of people worldwide. GIS is taught in schools, colleges, and universities throughout the world. Professionals in every field are increasingly aware of the advantages of thinking and working geographically.
Courtesy-USGS
A working GIS integrates five key components: hardware, software, data, people, and methods:
Hardware
Hardware is the computer on which a GIS operates. Today, GIS software runs
on a wide range of hardware types, from centralized computer servers to
desktop computers used in stand-alone or networked configurations.
Software
GIS software provides the functions and tools needed to store, analyze,
and display geographic information. Key software components are:
Tools for the input and manipulation of geographic information
A database management system (DBMS)
Tools that support geographic query, analysis, and visualization
A graphical user interface (GUI) for easy access to tools
Data
Possibly the most important component of a GIS is the data. Geographic data
and related tabular data can be collected in-house or purchased from a commercial
data provider. A GIS will integrate spatial data with other data resources
and can even use a DBMS, used by most organizations to organize and maintain
their data, to manage spatial data.
People
GIS technology is of limited value without the people who manage the system
and develop plans for applying it to real-world problems. GIS users range
from technical specialists who design and maintain the system to those who
use it to help them perform their everyday work.
Methods
A successful GIS operates according to a well-designed plan and business
rules, which are the models and operating practices unique to each organization.
How GIS Works
A GIS stores information about the world as a collection of thematic layers that can be linked together by geography. This simple but extremely powerful and versatile concept has proven invaluable for solving many real-world problems. The Figure below shows an actual screen shot of archaeological database of Egypt combined with roads, terrain data and a satellite image overlay. By clicking on any point of interest, data about it is made available to the user.
Click for larger image (180k) GIS Data of Archaeological Sites in Egypt
Geographic References
Geographic information contains either an explicit geographic reference,
such as a latitude and longitude or national grid coordinate, or an implicit
reference such as an address, postal code, census tract name, forest stand
identifier, or road name. An automated process called geocoding is used
to create explicit geographic references (multiple locations) from implicit
references (descriptions such as addresses). These geographic references
allow you to locate features, such as a business or forest stand, and events,
such as an earthquake, on the earth's surface for analysis.
Vector and Raster Models
Geographic information systems work with two fundamentally different types
of geographic models--the "vector" model and the "raster"
model. In the vector model, information about points, lines, and polygons
is encoded and stored as a collection of x,y coordinates. The location of
a point feature, such as a bore hole, can be described by a single x,y coordinate.
Linear features, such as roads and rivers, can be stored as a collection
of point coordinates. Polygonal features, such as sales territories and
river catchments, can be stored as a closed loop of coordinates.
The vector model is extremely useful for describing discrete features, but less useful for describing continuously varying features such as soil type or accessibility costs for hospitals. The raster model has evolved to model such continuous features. A raster image comprises a collection of grid cells rather like a scanned map or picture. Both the vector and raster models for storing geographic data have unique advantages and disadvantages. Modern GISs are able to handle both models.
Bible Archaeological Applications
Databases detailing climbing expeditions and associated imagery (photos and video) can be combined with Digital Elevation Models (DEM) and overlaid with satellite and aerial photos. Multispectral or hyperspectral imagery can be analyzed using classification algorithms to identify surface objects. This data can be combined with thermal IR imagery, to evaluate by thermal surroundings. The remote sensing imagery can be orthorectified and registered to fit on the DEM. We would then have a geospatial "fish net" model combined with actual imagery. SAR imagery and GPR data could also be added to reveal subsurface features. This data can be displayed 3 dimensionally and even "fly throughs" produced. This kind of technology can help answer the long sought after question "Where is the final resting place of Noah's Ark?"
Global Positioning System (GPS)
GPS measurements are useful for establishing the absolute location of data points. The data points could be used as a data overlays on the GIS maps. Remote sensing data such as Ground Penetrating Radar (GPR) readings can be correlated with GPS allowing the measurement locations to be shown on a GIS map. The GPR data can then be analyzed geographically. Other uses include establishing known reference points for aerial and satellite images, photographs, video, hiking trails, and documentation of climbing expeditions.
Courtesy Trimble
Multispectral and Hyperspectral Imagery
Multispectral imagery allows us to use filters that filter light into selected frequency bands. These filters are sensitive to a number of bands of light that passes through the filter (and rejects unwanted light frequencies). Therefore, by using a combination of filters, objects can be classified by their response (or lack of) to the bands of light (wavelength) that are allowed to pass through the filters. This technique has been useful in applications such as crop detection and mineral detection.
Hyperspectral imagery is composed of multispectral images in many, very narrow, contiguous spectral bands throughout the visible, near IR, and mid IR portions of the spectrum. Hyperspectral images can be composed of 200 or more channels of data. Imaging requires a hyperspectral camera, which is capable of separating light into the contiguous spectral bands. Processing can be accomplished on a computer that has software with special algorithms. Hyperspectral imagery can detect objects such as wood, rock and even identify petrified wood. It can also identify species of wood.
Hyperspectral data can be represented as a cube. In this case,
the top of the cube is a quasi-natural color image made from the reflectances
associated with three narrow spectral channels in the visible wavelengths
of light. On the left and right front sides are color representations of
the spectra for each of the pixels located along the lines joining the top
image with the spectral dimensions. The top corresponds to the low end of
the spectrum and the bottom the high end. Blacks through purple and blue
are assigned to low reflectances; yellows through red and then white denote
high reflectances. The area shown was imaged by AVIRIS during an aircraft
flight over the southern part of San Francisco Bay. Landing strips at Moffett
Field next to NASA's Ames Research Center locate that part of the image
within Mountain View, Calif.
NASA
The above photos show how various crops can be determined from hyperspectral imagery. Materials can be classified by their spectral properties. Multispectral and hyperspectral imagery can benefit archaeological research by analyzing surface features. High resolution imagery could reveal any exposed material.
Thermal IR
Thermal Infrared (IR) can photographically measure direct temperature effects of objects, by sensing radiation emitted from solids, liquids, and gases in the thermal infrared region of the spectrum.Thermal IR sensing of solids and liquids takes place in two "windows" of the atmosphere where absorption is at a minimum. The windows normally used from aircraft platforms are in the 3 - 5 µm and 8 - 14 µm wavelength regions; windows between 3 and 4 mm and between 10.5-12.5 µm are commonly used on spaceborne sensors.
All matter (above 0 deg Kelvin) absorb and radiate thermal energy. By making photographic measurements of these properties, we can gain important information about objects. The figure below shows absorbsion and radiation of various materials throughout a 24 hour period.
Courtesy NASA
Thermal IR imagery would benefit archaeological research by identifying surface features by their thermal characteristics. For example, various exposed or slightly covered-over rocks and wood could be viewed.
Subsurface Measurements
Ground Penetrating Radar
Ground penetrating radar (GPR) utilizes radio waves to penetrate the ground. Unlike conventional radar, GPR equipment is typically mounted on a cart or sled and moved over the area to be surveyed. This results in a series of measurements which are analyzed by the operator. GPR equipment doesn't produce a traditional image like radar does. Instead it produces a plot showing distance vs depth. GPR would be extremely useful when combined with SAR data for verification of any archaeological candidates discovered in the SAR imagery. A GPR plot taken in Antarctica is shown in the figure below.
GPR typically operates in a frequency range of 75 to 500 MHz. The lower frequencies allow better ground penetration while the high frequencies allow for smaller antennas and more portability. Ground Penetrating Radar concepts have been in use for more than 20 years in contrast to more than 50 years for conventional radar systems. GPR has been used in archeological research for many years and has been very beneficial in some areas while unproductive in others. It was used to survey the Great Pyramid, but was unable to penetrate it due to its high conductivity. However, ice has electrical parameters which permit GPR probing with significant penetration. Ice also has a complicated morphology with layering and other structure which can provide information on past weather conditions. GPR was successfully utilized in detection of buried WW II aircraft in the Greenland ice cap. It was also used to survey the Eastern Plateau of Mt Ararat in 1988. Future plans include measurements using GPR in other areas on Mt. Ararat. It would be a great advantage to log the GPR data with GPS data. Mt. Ararat's rugged terrain and a past history of access problems could make this a difficult and time consuming process to survey the entire mountain.
Ice Penetrating Radar Image of land beneath Antarctic Ice
Radar Imagery
The origins of SAR go back to the development of radar during Wold War II. Radar which is an acronym for Radio Detection and Ranging. Unlike optical sensors, which passively sense reflected radiation, from the Sun or thermal sources, radar generates its own illumination. We refer to this as an active sensor. Radar sends out its own pulse of Radio Frequency energy. The energy strikes an object and is reflected back to a receive antenna. This reflection is displayed on an imaging device such as a radarscope (now days computers). We determine the distance to a target by timing the pulse. We start our clock when the radar pulse is transmitted and stop it when the pulse is returned. After dividing by two (for return distance) we now know how far away the target is. Radar also transmits its energy in narrow beams. The beamwidth helps reduce the scattering effect, thus helping to resolve the target. During the World War II era, it was discovered that an airborne radar antenna could be pointed at the ground, and an image would be produced of the ground even when clouds obscured ground visibility. This became known as radar navigation.
Aircraft radar imaging antennas are usually mounted on the lower sides of an aircraft fuselage. In this way, the beam can be directed at 45 degrees. This concept became known as SLAR (Side Looking Airborne Radar). A real aperture SLAR system operates with a long (~5-6 m) antenna usually shaped as a section of a cylinder wall. This type produces a beam of noncoherent pulses and utilizes its length to obtain the desired resolution (related to angular beamwidth) in the azimuthal (flight line) direction. At any instant the transmitted beam is propagated outward within a fan-shaped plane perpendicular to the line of flight.
A second type of system, Synthetic Aperture Radar (SAR), is exclusive to moving platforms. It uses an antenna of much smaller physical dimensions, which sends forth its signals from different positions as the platform advances, simulating a real aperture by integrating the pulse "echoes" into a composite signal. It is possible through appropriate processing to simulate effective antennae lengths up to 100 meters or more. This system depends on the Doppler (frequency shift produced by movement) effect to determine azimuth resolution. As coherent pulses transmitted from the radar source reflect from the ground to the advancing platform (air or spacecraft), the target acts as though in apparent (relative) motion. This motion results in changing frequencies, which give rise to variations in phase and amplitude in the returned pulses. Digital Signal Processing (DSP) methods are used for correlation processes in which the pulses can be analyzed and recombined to synthesize signals equivalent to those obtained by a narrow beam, real aperture system.
SAR Imagery
Images produced from SAR data provide researchers aerial imagery of their areas of interest. The image below shows the area surrounding the Dead Sea along the West Bank between Israel and Jordan. A portion of the Dead Sea is shown as the large black area in the image. The Jordan River is the white line at the top of the image which flows into the Dead Sea. The yellowish area in the upper left corner is Jericho. This image was take from the space shuttle Endeavour with the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on October 3, 1994.
The radars illuminate Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The colors are assigned to different radar frequencies and polarizations as follows: red is L-band, horizontally transmitted and vertically received; green is L-band, horizontally transmitted and horizontally received; and blue is C-band, horizontally transmitted and vertically received. The SIR-C/X-SAR data can be complemented by additional imagery and ground studies to provides researchers additional data for their analysis.
SIR-C SAR Image of the Dead Sea Area
Click here for larger image (200 K image)
IR enhanced LandSat image of the Dead Sea and Jericho
Ice Penetrating Radar for Remote Sensing
Advances in digital signal processing technologies enable us to use SAR technology to see beneath forest canopies, ground, and ice. Such SARs are known as FOPEN SARs (Foliage Penetrating). These types of SARs operate at much lower frequencies than conventional SARs. FOPEN SARs could be useful for ice penetration applications, since the radio waves are capable of penetrating ice, such as glaciers. Mt Ararat is covered with a glacier that never entirely melts. Therefore, this technology could be very useful in the search for Noah's Ark.
Depiction of SAR Equipped Aircraft Surveying Mt Ararat
SAR Ice Penetration
Last Updated 2-03-2005
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