GPR Ground Penetrating Radar

Ground Penetrating Radar (GPR) is a tool archaeologists will use more and more for excavations in the 21st century. GPR allows archaeologists to survey archaeological sites in a short amount of time with precision and without digging.

Basic Principles Uses radio waves to create picture of underground before excavation Picture is used to locate any variations in the sub-surfaces

Basic Mechanism Electrode magnetic waves emitted into the ground and time measured for wave to be reflected and received When wave hits areas of change in soil, it is hit back to receiver antenna Changes in soil can include objects buried underneath the surface

Greater surface difference = Stronger signal Strong signal has large amplitude Weak signal has small amplitude Amplitude wavelength and time are used to create image of what is underground

RDP Relative Dielectric Permitivity “RDP is ability of a material to store and allow passage of electromagnetic energy when a field is imposed upon it.” RDP of a substance = electrical permitivity / vacuum

K = RDP C = Speed of light V = Velocity of radar energy

GPR Depth Determination D = (5.9t)/sqrt of (Er) Dielectric constants for common materials D = depth of target (in) t = wave travel time (nanosec) 5.9 = a constant incorporating speed of light and unit conversions Er = dielectric constant of subsurface material Air 1 Pure water 81 Fresh water (ice) 4 Granite (dry) 5 Clay (saturated) 8-12 Sand (dry) 4-6 Sand (saturated) 30

Example How deep below the surface is an object that is detected at 46 ns in dry sand (Er = 4)? Answer: D = (5.9 x 46) / sqrt (4) D = 135.7 in Therefore the object is about 11 ft underground

Equipment Consists of: 1. control unit 2. display unit 3. transmitting and receiving unit

Case Studies Cave of Letters Bethesaida, Israel Forum Novum

Cave of Letters Site located in Nahal, Hever (a canyon by the Dead Sea) GPR was used to map possible excavation sites in the Cave of Letters

Artifacts Found Coins Clothes Letters mentioning Jewish leader Bar-Kokhba who had fought against the Romans around the middle first century

Bethesaida, Israel Located in Northern Israel near the sea of Galilee Was an active fishing community 2000 years ago Site where Jesus healed a blind man and walked on water

Overview Movie http://www.joeinfo.com/gpr/overview.MOV

Bethsaida Excavation GPR has tested land for cave locations Artifacts found: 1. coins (dated as far back as 1st and 2nd Century) 2. child’s sandal 3. fabric 4. pottery 5. human bones and remains

Antenna Movie http://www.joeinfo.com/gpr/antenna.MOV

Recently, Dr. Harry Jol, professor of geography at the University of Wisconsin - Eau Claire, used GPR to map an area by the city gates of Bethsaida

Vescovio, Italy Romaneque church of Santa Maria Remains of marketplace, living quarters, storage areas, hallways and door entrances reconstructed visually

Forum Novum Remains of marketplace, living quarters, storage areas, hallways and door entrances reconstructed visually Believed to be Roman marketplace which initially began construction in the 1st century BC and flourished through the 4th century AD as the Roman town of the Forum Novum

Excavation British School of Archaeology in Rome have conducted excavation sites Sites include: 1. an amphitheatre 2. a bath complex 3. the villa 4. a tomb complex 5. crypts from the 8th to 9th centuries located behind the church

GPR reading from Forum Novum

Wrap up… GPR usage has become more wide-spread Now used in construction Average person can now purchase GPR equipment