Trough

Figure 2. Entire trough used for sand transmission tests.

Sound transmission in geological materials

Mikel-Stites M.1,2, Ulrich R.2,3, El Shafie A.2 1 Dept. of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, 2 W. M. Keck Laboratory for Space Simulation, Arkansas Center for Space

and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, 3 Dept. of Chemical Engineering, University of Arkansas, Fayetteville, AR 72701

Conclusions Acoustic transmission is a potentially viable option

for subsurface depth measurements and possibly more detailed mapping

There are still problems to overcome

- Attenuation in loose media

- Differentiation between surface and subsurface waves

- Distortion The energy required to produce a usable signal for

large depths may be significant.

Future Work

• Further experimentation with transmission through various materials, especially combinations of materials

• A change from mechanical pulse generation to sonic generation (speakers) as well as extended tones.

• Vertical test chamber with surface microphones

• Differentiation between Rayleigh and P waves

• Testing resonance methods as an alternative to pulse generation

Introduction

•The purpose of this project is to ascertain the feasibility of sonic imaging of subsurface geological layers of Mars by examining the transmission of sound waves through various materials.

•The objective is to measure the velocity of sound in the materials tested based on the time delay in the reception of the sound wave between them. In the future, a similar technique could be used to measure the depth of surface layers.

•In order to do this, we are developing methods to measure the speed of sound through various geological material including icy regoliths. The development of these techniques are described here.

•The steel plate is hit with a hammer

in order to produce a pulse of sound

which will run the length of the trough

The trough is roughly2.46 meters long and

filled with sand to awith sand to a depth

of approximatelyof .178 meters

Data and DiscussionSound in sand

•Pulse produced by hitting the steel plate placed on top of the sand with a hammer

•Same process used to record the pulse, using contact microphones

•High degree of attenuation

•More distortion

•More difficult to analyze waves

Sound in air

•A pulse was made by clapping hands in front of the first microphone (top line)

•The wave travels through the air until it reaches the second microphone.

•X axis is time, Y axis is amplitude

•Some attenuation is visible, but velocity can be determined by the time it takes for the pulse to travel the distance between the microphones

•The distance between the microphones is approx. 5.87 meters and since the time delay is 0.016 seconds, we can calculate the velocity to be approximately 366.72 m/s, which is a little high compared to 346 m/s for room temperature, but likely due to error in measurement.

Discussion

•Best transmission medium in terms of distortion and attenuation has been air. However, thus far, reception of surface (Rayleigh) waves has impaired signal processing and accurate measurement of sound speed in the other media.

•High transmission speed materials, such as concrete, also increase error since the time interval is significantly smaller.

•Thin, densely packed layers may provide a similar challenge in signal processing.

•Because of the high speed of sound in concrete, the time difference between the first and second microphones is so small (approx. 0.02948 seconds) that it is difficult to get an accurate measurement of the velocity.

Sound in concrete

•Pulse made by hitting the floor with a hammer

•Rapid propagation

•Little distortion

•Some attenuation

Acknowledgments I would like to acknowledge Dr. Rick Ulrich, Ahmed El Shafie, Robert Pilgrim and Walter Graupner for their assistance with this

project would also like to thank the University of Arkansas and the Center for Space and Planetary Sciences for making this research possible.

Methodology

•Microphones were placed a measured distance from each other on or in the chosen material

•The surface was struck with a hammer just before the first microphone to produce a sound pulse which could be measured.

•The pulse was recorded using SoundStudio and a Macintosh computer and analyzed using the same program.

•The time interval between the arrival of the pulse at the first microphone and its arrival at the second microphone.

Trough and steel plate

Figure 1. Steel plate in trough used for sand test