Ground penetrating Radar

Question 1

Ground Penetrating Radar (GPR)

Answer 1

• Uses Radio waves which are applied to the ground from
  a transmitter
• Radio waves are transmitted, then absorbed by the
  ground or scattered
• A sound pulse is emitted and reflect sound is detected
• Distance = time it takes for reflected sound/pulse
• Direction = information provided by turning radar
• Frequency of 100 MHz to reduce absorption by salt
  water
• Pulse is short - Distances are short
• Depth limited to a few metres as soil and rocks absorb
  radio waves
• Non-directional, radar equipment moved to find targets
• Use the highest possible frequency while assuring the depth required is achieved

Question 2

Attenuation

Answer 2

• the amount of absorption
  Attenuation = I0/It

WHERE:
I0 = initial signal intensity
It = signal intensity after 1 metre
dB (decibel) = factor of 10

Question 3

GPR Equipment

Answer 3

How it works:

• a radiowave pulse is created by discharging a capacitor
• Sending (T) and Receiving (R) antennas are mounted face down
• Mounted on a small cart (or a compact handheld device)
• Works best on flat surfaces
• Most expensive equipment of all geological methods

Question 4

Use to detect …

Answer 4

• Changes in density of material
• A body buried under a concrete
• Can detect buried firearms
• Useful in checking below concrete before excavation

Question 5

Uses of GPR

Answer 5

• Depth information
• Measured along survey lines
• Fast search can be conducted at walking pace, 2m
  spacing of survey lines.
• Computer processing to show survey results
• 3D information can be obtained if multiple survey lines
  are present
  IN FORENSIC SCIENCE:
• Different frequencies used (200, 400-500 or 900 MHZ)
• Compromise between soil penetration and resolution
• Can detect 5cm cavity at 1m depth
• Can detect large objects at 3m depth
• Can penetrate = Flooring, concrete or tarmac
• Cant penetrate = clay, salt water or sheet metal