What does gpr stand for?

Ground Penetrating Radar (GPR) is the general term applied to techniques which employ radio waves, typically in the 1 to 1000 MHz frequency range, to map structures and features buried in the ground (or in man-made structures). Historically, GPR was primarily focused on mapping structures in the ground; more recently GPR has been used in non-destructive testing of non-metallic structures.
 

The concept of applying radio waves to probe the internal structure of the ground is not new. Without a doubt, the most successful early work in this area was the use of radio-echo sounders to map the thickness of ice sheets in the Arctic and Antarctic and sound the thickness of glaciers. Work with GPR in non-ice environments started in the early 1970s. Early work focused on permafrost soil applications.
 
GPR applications are limited only by the imagination and availability of suitable instrumentation. These days, GPR is being used in many different areas including locating buried utilities, mine site evaluation, forensic investigations, archaeological digs, searching for buried landmines and unexploded ordnance, and measuring snow and ice thickness and quality for ski slope management and avalanche prediction, to name a few.

How does it work?

1. Emits weak radio frequency signals
2. Detects the echoes sent back and uses them to build an image
3. Displays signal time delay and strength

GPR is just like a fish finder & echo sounder

1. The finder sends out a ping
2. Signal is scattered back from the fish
3. Signal is scattered back from the bottom

1. As the boat moves it collects recordings
2. The recordings are displayed side by side
3. The result looks like a cross section

GPR Exploration Depths

Exploration depth is site specific

• soils absorb radio waves
• sands and gravel are favorable for GPR
• fine-grained soils such as silt and clay absorb signals
• salty water is totally opaque

What’s so tough about GPR?

1. The ground is more complicated
2. Man-made structures are complex
3. Some things simply do not reflect
4. Some grounds absorb all of the signals

Why doesn’t the pipe look like a pipe?

• the GPR record is a pseudo image of the ground
• localized features become hyperbolas (inverted V’s)
• the GPR sends signals into the ground in all directions
• echoes are observed from all directions
• closest approach (over target) occurs at the apex of V
• the shape of inverted V helps determine the exact depth