converting sonar for seismic use?

[Randy Seden]

Carl and group,

How hard would it be to convert a sonar unit to send sound thru the earth to locate bedrock? This would be a very hot item that has alot of economic potential for the inventor. Seems to me it would take adjusting the software to calculate the velocity of soil as opposed to water. Any ideas? Or does anyone know of software that allows you to use the pc soundcard inputs for a simple reflective seismic measurement?

Randy Seden

[Raymond]

Re: converting sonar for seismic use?

There are several systems that do this already, depending on how deep you want to go and whether or not you are in water. The problem with sidescan is that most are 50 KHz or above and so do not penetrate the bottom.

Sub bottom profilers are low frequency acoustic devices that will penetrate the seabed, they can be towed like a sidescan; resistivity sytems use electric currents to generate resistivity profiles of the strata which can then be used to generate sub bottom images and some low frequency echosounders will penetrate the bottom up to 60m depending on the frequency and power output.

The resistivity system is the only one that can truly tell you where the bedrock is as the others bounce sound off the rocks and would not penetrate a bit of "broken" bedrock. I have see this is South Africa where a SBP indicated the bedrock formation but a resistivity survey proved that a large part of the original bedrock had brocken away. This then had to be removed before the area was suitable for construction.

[Randy Seden]

Re: converting sonar for seismic use?

Thank you for your reply. What I had in mind was a standard sonar fish finder being converted to a land seismic by changing the time contants, has someone tried that? The maximum depth I'm looking at is 60'.
I would appreciate any further ideas as I cannot justify the cost of standard seismic. Sure would be neat also to just use the soundcard of a pc with 2 geophones for reflective shots.

Randy Seden

[Carl-NC]

Re: converting sonar for seismic use?

I believe there is an issue of acoustic impedance mismatch. That is, you would need the ultrasonic transducer to be buried in the soil, possibly even in a matching gel, much like is done with medical ultrasound. I suspect fish finder transducers are optimized for water use only.

- Carl

[Teo]

Re: converting sonar for seismic use?

You need ground penetrating radar (GRP)