Sound+And+Terrorism

Can low frequency sonar be used to locate underground combatants such insurgents of terrorists?
 * Research Question**:

In the modern era, nation against nation warfare is rare, and doesn’t pose a large threat to the developed nations of the world. It has been replaced by more insidious and covert operations that are carried out by small, decentralized groups. These groups are almost impossible to fight by traditional means because they are hard to find. They use the terrain to their advantage. New tools are need by the military to locate these combatants and bring them to justice in such hot zones as the mountainous areas of Pakistan, Afghanistan, and Iraq. With this project, we will explore the possibility of using sonar-like technology to locate underground combatants. Due to resource constraints, no quantitative experimental data on ground piercing data could be gathered. The technology does not exist, and the closest possible piece of technology would be dangerous and expensive to use. However, we chose to explore the possibility of this technology in a number of different ways. First, we examined the underlying physical principles of sound propagation and reflection upon which sonar is based and how they apply to ground piercing sonar. Second, we examined related technologies currently available, how they work, and how they might apply to the research question. Last we conducted a scaled down proof of concept study using an aqueous terrain and an ultrasound device. Through these methods of investigation we hope to arrive at an, if not definitive, at least educated answer to our research question.
 * Introduction:**

Yes, Low frequency sonar-like devices could be used to locate underground combatants
 * Hypothesis:**

**Proof of Concept Test:** As part of the project we have created several small demonstration pictures. These pictures all demonstrate how a portable sonar device views various objects in an aqueous simulated terrain. a picture of the simulated will be posted later with an explanation. The terrain had to be aqueous due to the limited range of frequencies employed by the device. Water transmits sound waves better than earth and it can transmit higher frequencies without random scattering or just bouncing them back. Each of these pictures views one of several objects at one of two possible frequencies. I believe these picture illustrate well some of the advantages and disadvantages of sonar technology. These videos also illustrate several basic sonar principals such as the negative correlation between frequency and image resolution and the difficulties involved in generating sound waves the don't reflect off of solid surfaces. More of the pictures will be on the board, than will be posted on the website. Each picture will be given a caption and an explanation of how it pertains to sonar. Here is a picture of the aqueous terrain. One can observe a layer of foam at the top. The middle layer is made of sponges, and the bottom layer is covered in rocks and sand. The device was constructed of substances of varying density and grit in order to show contrast in the sonar photos. Air filled tubing was also buried in the device in order to show what insurgent caves might look like in sonar images. This is another picture of the device from the top this time. I looks like an elegant brown rectangle with tubing, the most sonorous of shapes.

In this picture one can see the lengthwise image of two tubes. They appear as long lines of slightly brighter than average material. One goes from the bottom center of the screen to the lower right area. The other has a similar trajectory right above the first. The bright white area at the bottom right center area of the screen is either an air bubble or a fold in the tube. The tubes are a brighter color in these images because the plastic reflects sound. Actual caves would be darker than the surrounding rock because they reflect less sound.

This last image is different from the others because the sound for this one was emitted at 3 megahertz rather than 5. As a consequence the wave goes through most things instead of reflecting off of them. Only a tube is really visible because it is the most reflecting thing in the tank. The area below the tube is brighter because of the sound shadow cast by the tube. The highlights of rocks can also be seen near the bottom where the sonar has a hard time penetrating.


 * Background Information:**

Basic Question Info: The speed of sound traveling through a medium is represented by the equation: speed through medium= wavelength x frequency. However, this equation cannot be directly usefull in terms of sound's effectiveness in finding underground terrorists. The fundamental concept that this equation is based on is that the medium is somewhat uniform, such as water or air might be. "Ground" itself is a general term; the composistions of "ground" vary from region to region. Furthermore, soil and rock are, in themselves, not even slightly uniform, thereby skewing the results derived from this equation. Based specifically on the relation of speed through a medium and wavelength x frequency, sound waves from such machines as an ultrasound cannot be used to locate underground terrorists.

Sonar Propagation through Various Substances: Common frequencies for sonar are 200 or 400 KHz for most fresh water and salt water applications. However, water has a better tendency to absorb high-frequency sound waves than low-frequency waves. This means that the reflected signal of low-frequency sonar is stronger than that of high-frequency sonar. For this reason, 32KHz or 50KHz sonar frequencies are used for probing greater depths and longer distances. However, these signals will reveal less detail in the space between the point of transmission and the point of reflection because their relative strength allows them to penetrate more material without being absorbed or reflected. Therefore, resolution is generally lower for low-frequency sonar. Objects that it encounters between transmission and reflection are indistinct, more difficult to recognize. Low-frequency sonar can also be transmitted through denser materials because of the same properties as mentioned above. The relative strength of the sound waves allows propagation through materials that would immediately reflect higher-frequency sonar. This is the basis for the hypothesis of our research. The possibility of locating subterranean caverns or bunkers is real, but difficult. The propagation of low-frequency sonar through rock is considerably less predictable than its propagation through water. Pockets of different kinds of rock can lead to confusion about the reflected image as different rock types have different physical properties. Also, the ground would need to be a fairly aqueous environment for the sound waves to travel any considerable depth, as rock simply does not propagate sound waves efficiently due to the rigidity of solid matter. However, some basic rules are listed below: f = (T,p,S) where c(T,p,S) is the speed of propagation as a function of temperature (T), pressure (p) and salinity (S). A few general rules to remember are that
 * 1 degree C**elsius increase in temperature produces about **3 m/s** increase in speed.


 * 100 meters** of depth increase produces **1.7 m/s** increase in speed.


 * 1 ppt** (part per thousand) increase in salinity produces **1.3 m/s** increase in speed.

More useful information: wavelength = speed of sound in the medium/ frequency Speed of sound through water is roughly 1500 air is roughly 340

Thumper Devices Guest Written By Ryan Stroud The sound nature of a thumper device is to generate immense sound vibrations. The vibrations then go through the rock. Different types of rock create different reverse vibrations as the sound bounces back off the rock and the vibrations return to the thumper device. Then this allows the people using the super to determine the composition of the rocks that the thumper is being used on. Thus, thumper devices can determine the composition of underground rock with out having to exhume them. One problem with thumper devices are how inaccurate they sometimes are because of the similar nature of rock structures. One needs to take thumper devices with an air of inaccuracy in order to get the most benefit from them


 * Related Technologies:**

** Technology and Applications ** We’ve all heard of military applications of sonar in the Navy; particularly its use to locate submarines. However, sonar technology has also been applied to many other useful situations. This includes Obstetric Ultrasounds, in which high frequency sound waves are sent from the exterior into the womb and the reflected waves are used to create an image. These sonograms allow doctors to examine the developing child for abnormalities or any other issues that may be afflicting the baby, and act accordingly. Modern sonograms have been perfected to the point that 3-dimensional pictures can be generated from recorded sound waves. Ultrasounds are particularly used to check for heart development abnormalities. In addition to the medical field, sonar technology has also been applied for convenience in the commercial market. Before the development and extensive use of infrared technology, sonar was used in auto-focus devices in cameras made by Polaroid. The camera would send out sound waves and use the reflected waves to measure distance to determine how to focus accordingly. Though problems arose particularly when one was taking pictures through windows, it was a start, and the concept of reflection is used in modern cameras today using infrared. An application of sound waves through rocks to survey and map out under-surface environments such as caves would be similar to that of application of shock waves. Much of oil surveying over land is done through the use of shock-wave reverberation. Whole trucks are designed to slam heavy plates into the ground to send shock waves into the ground, and reflect back to detection and measurement arrays. Thus, a rough image can be mapped out. However, this technology, though better than its predecessors is still relatively inefficient. The success of accuracy rate of this seismic technology is only around 10%. The estimated success of underground mapping devices employing sonar is a bit higher, given that shock fronts are nonlinear waves that abruptly change the state of the approaching medium, while sound w aves are small-amplitude compression waves that propagate at the local sound speed and leave the state of the medium (media) unchanged. This would garner better results, but the variability of frequencies of sound waves to be employed and their nature at different depths and densities still poses a significant problem (see conclusions.) Last, but not least, is the potential application of sonar triangulation technology in robotics. Already there are prototypes for sonar devices mounted on autonomous robots that would be sent into deep sea environments to survey the area in preparation and/or maintenance of civil structures such as underwater pipelines. This would alleviate a demand for manpower in addition to increasing efficiency for the laying of those pipelines. Already are there arrays being designed for deep ocean environments that take into account pressure, salinity, and temperature of the depths.

Discussion: So, after all this examination, would it be possible to use sonar to locate underground combatants? It certainly is possible to examine the subterranean world with sonar like devices, but most of those devices are designed to locate huge underground geological structures, not little caves. As was mentioned earlier, lower frequencies can go through more things, but, as a consequence, they don’t reflect back off of small objects, so they don’t show up on lower frequency sonar. The low frequencies of the waves necessary to travel a long way through the rock would mean that the device probably wouldn’t show any small caves. The image quality is further reduced by the fact that most thumper devices use one blast to generate sound rather than creating constant noise. This means that the device won’t be able to remove errors by averaging the reflections over multiple cycles. However, if a large terrorist cell were hiding out in a large cave not hugely far beneath the surface, Sonar technology could find that cave, but you might have to know where to look first. Unfortunately, in order to attain the amplitude of the wave required to get through all that rock most of such devices focus their sound waves in a narrow cone less dispersed the cone is, the less area is being affected by the initial energy. Less area at the base of the cone means less initial energy is needed. Since a huge amount of energy would be needed to blanket large areas in sonar we would have to already know mostly where the caves were to find them. One possibility would be creating an array of low frequency sonar devices. Such an array would of course increase the area covered, but that’s not all. An array would also increase accuracy and image quality because the images could be cross referenced and averaged. The benefits of using an array might be enough to counteract many of the problems mentioned earlier. Still, insurmountable problems exist. An array would be extremely difficult and costly to deploy. Also, such an array would have no way of telling if a cave was occupied by terrorists or not. The mountains of Afghanistan are riddled with caves and the vast majority of them are unoccupied. Also, most of the air pockets picked up by the array probably wouldn’t even be connected to the surface. There are probably hundreds and hundreds of underground air pockets that a sonar device could pick up. Conclusion: So what does it all mean? It means that there is very little possibility that sonar could help find caves, and, if it could, it would probably find so many that it wouldn’t significantly aid in the search process. These problems, combined with the cost that such a system might entail, lead us to conclude that such a solution would be impossible or at least impractical.

Bibliography: Russel, Mark. "Sonar and How it Builds a Spacial Mapping through the use of sound." 2007.http://web.arch.usyd.edu.au/%7Edensil/DESC9137/Russell.pdf (accessed 10/23/08).

Central de Lyon, Ecole. "The Propagation of Sound." 1998.http://www.jhu.edu/virtlab/ray/acoustic.htm (accessed 10/23/08).  "Acoustic Location." __Acoustic Location__. 08. Wikipedia.org. 7 Sept. 08 .

"Bathymetry." __Bathymetry__. 08. Wikipedia.org. 14 Oct. 08 .

Broholm, Colin. "Wave-equation for sound propagation in a fluid." 11 Nov. 97. PHA. 25 Oct. 08 <[|http://www.pha.jhu.edu/~broholm/l28/node4.html]>.

"Listening Closely to 'See' Into the Earth." __Oceanus__. 5 Mar. 04. Woods Hole Oceanographic Institution. 25 Oct. 08 .

"Low Frequency Active Sonar." __Low Frequency Active Sonar__. 08. NURC. 7 Sept. 08 .

"Multibeam Echosounder." __Multibeam Echosounder__. 08. Wikipedia.org. 3 Oct. 08 .

"Propagation of Sound." __The Propagation of Sound__. Autumn 04. 11 Nov. 08 .

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Members: Nate Neligh and James SC Sze

Guest Starring: Ryan Stroud, Chris Lowe, Will Paces, and PCP

Log Sheet

Nate Sze Nate Nate Nate Nate Nate Sze Sze and Nate || Oct 21 Nov 11 Nov 16 Nov 17 Nov 29 Dec 1 Dec 2 Dec 3 Dec 3 Dec 4 || 2:00 4:14 1:07 6:33 5:58 5:54 9:04 6:55 6:43 2:30 || Investigated sound propagation Updated demonstration type. Found 2 sources for theoretical devices in robotics applications. updated demonstration info More updates. What video and picture formats are supported and how do I post video? Minor trimming and edits. Decided to go with pictures instead. Uploaded 2 pictures. Uploaded more pictures. Major updates, added intro, discussion, conclusion Wrote on applications and sonar technology, thumper devices, and found photos. Project is relatively finalized. ||
 * Name(s) || Date || Time || Content ||
 * nate || sept 27 || 8:30 || assignment ||
 * nate || sept 30 || 8:19 || assignment ||
 * Nate || Oct 3 || 1:33 || assignment/new member ||
 * Asian || Oct 3 || 1:34 || added to team to the thunderous applause of the team ||
 * Nate || Oct 4 || 9:00 || minor layout and font repairs ||
 * Minority || Oct 6 || 7:05 || Found some articles regarding Sonar Triangulation. ||
 * Nate || Oct 20 || 3:46 || small update ||
 * Nate || Oct 21 || 1:40 || added source, updated experiment ||
 * Ryan || Oct 21 || 1;55 || Added research info and discussed with team mates. ||
 * Chris || Oct. 21 || 1:56 || added source regarding low-frequency sonar and its modern day use ||
 * Will