Chapter 9 

Government secrets of the oceans,
atmosphere, and UFOs

(Last updated 10/26 with link to Project Mogul picture)
© 2001 Richard A. Muller

Index for this chapter:

Flying saucers
Rescuing pilots
Back to rescuing pilots
Sound channel and whale songs
GPS
The Cold War -- and SOSUS
Sound -- doesn't travel straight
Sound channel explained
Atmospheric sound channel
Project Mogul
The flying disks crash

"Flying Saucers" crashed near Roswell New Mexico in 1947!

Strange but true: In 1947, devices that the U.S. government called "flying disks" crashed in the desert of New Mexico.  The debris was collected by a team from the nearby Roswell Army Air Base, which was one of the most highly classified locations in the United States.  The government put out a press release announcing that flying disks had crashed, and the story made headlines in the respected local newspaper, the Roswell Daily Record. Take a moment to look at the headlines for July 8, 1947: RAAF Captures Flying Saucer. (RAAF stands for Roswell Army Air Force.)

The next day, the U.S. Government retracted the press release, and said it was in error.  There were no flying disks, the government said.  "It was only a weather balloon."

Anybody who had seen the debris knew it wasn't a weather balloon.  It wasn't.  The government was lying, in order to protect a highly classified program. And everybody knew the government was lying.

The story I have just related sounds like a fantasy story from a supermarket tabloid -- or maybe like the ravings of an anti-government nut. But I assure you, everything I said is true. The story of the events of Roswell New Mexico are fascinating, and not widely known, since many of them were classified until recently.   In this chapter I'll fill in the details that will make the Roswell story make sense.

(Incidentally, if you are unfamiliar with the name Roswell, that means you have not watched the TV program "The X-Files" or read any of the other voluminous literature about flying saucers and UFOs.  Try doing a web search on Roswell 1947 and see what you find. Be prepared to be astonished.)

To understand what really did happen at Roswell, we will have to work through some other very interesting stories, including the history of the role of submarines in the cold war between the U.S. and Russia, details of whale communication, the effects of the ozone layer, the behavior of sound on a summer evening, and the design of modern fiber optics.

What does this have to do with physics? This is really an introductory chapter on the subject of waves: sound waves, light waves, seismic waves. To understand Roswell, we're going to have to understand what waves are, and why they don't always travel in straight lines.

 

Rescuing pilots shot down in World War II

The true story of the flying disks begins with an ingenious invention made by the physicist Maurice Ewing near the end of World War II.  The invention involved small objects called "Sofar" spheres that were in the emergency kits of pilots flying over the Pacific Ocean. If the pilots were shot down, but they managed to inflate and get on to a life raft, then they were instructed to take one of these spheres and drop it into the water. If they weren't rescued within 24 hours, then they should drop another.

What was in these miraculous spheres? If the enemy had captured one, and opened it up, they would have found that the spheres were hollow, with nothing inside. Nothing. How could hollow spheres lead to rescue? Can you guess how they worked?

Hint: they used the same phenomena that whales use to communicate with other whales.

Here's the answer: Ewing had been studying the ocean, and he was particularly interested in the way that sound travels in water. He knew that the temperature of the water got colder as it got deeper -- and that should make sound travel slower. But as you go deeper, the pressure gets stronger, and that should make the sound travel faster. The two effects don't cancel. When he studied it in detail, he concluded that the sound velocity would vary with depth. And his most interesting conclusion was that at a depth of about 1 km, the sound traveled slower than at any other depth. As we will discuss later, this implies the existence of a "sound channel" at this depth, a layer that tends to concentrate and focus sound and keep it from escaping to other depths. Ewing did some experiments off the coast of New Jersey, and verified that this sound channel existed, just as he had predicted.

What is sound? How can it travel in water? Sound in air results when air is suddenly compressed, for example from a moving surface (e.g. vocal cord or bell). The compression pushes against adjacent air, and that pushes against the air in front of it, and so on. The amazing thing about sound is that the disturbance travels, but the air returns to its original position. That is the feature of all waves.

Sound also results when anything is suddenly compressed. Suppose you hit a hammer on a railroad rail. The metal is compressed. The compression will travel down the rail. If someone puts their ear to the rail, a mile away, they will hear the sound as it passes them. Because steel is so stiff, it turns out that sound travels in steel much faster than in air. In air, sound takes 5 seconds to go one mile; in steel, sound will go that same distance in less than 1/3 second.

Sound travels in any material that is springy, i.e. which will return to its original shape when suddenly compressed. Water isn't very compressible, but it does compress more easily that steel. The speed of sound in water is about 1 mile per second, but it depends on the temperature and depth of the water.

A surprising but remarkable fact: The speed of sound doesn't depend on how hard you push; it depends only on the properties of the material being pushed! No matter how loud you shout, the sound doesn't get there any faster.

Why is that? Remember, at least for air, the speed of sound is approximately the speed of molecules. The signal has to go from one molecule to the next, and it can't do that until the air molecule moves from one location to another.

The table below gives the speed of sound in several materials:

material and temperature speed of sound
air at 0 C = 32 F 331 meters/sec  = 1 mile every 5 seconds
air at 20 C = 68 F
 343 meters/sec
water at 0 C 1402 m/sec
water at 20C  1482 m/sec  =  almost 1 mile per second
steel 5790 m/sec  =  3.6 miles per second
granite 5800 m/sec

Sound traveling in rock gives us very interesting information about distant earthquakes. We'll come back to that in a later chapter. Measurements of the surface of the sun show sound waves arriving from the other side. Sound has been detected traveling through the moon, created by meteorites hitting the opposite side.

There is no sound in space, despite science fiction movies, because there is nothing to shake. A famous tag line from the science fiction movie "Alien" was: "In space, nobody can hear you scream." The sound that traveled through the moon did not leave the surface, because there was no atmosphere to carry it. It was picked up by sensitive microphones left on the surface by the Apollo astronauts.

Puzzle: why is sound faster in warm air than in cold air? Look at the table above. Can you think of any reason why this is true? The answer is posted here, but see if you can figure out why. Try rereading the last section ("A surprising but remarkable fact"), and look for the clue.

 

Back to rescuing pilots

We have digressed a little from the Ewing invention, in order to discuss the properties of sound. Let's get back: what was the magic of Ewing's Sofar spheres?  They were hollow, and yet they were made of heavy material. Since they weighed more than an equal volume of water, they didn't float, but sank. (If the metal were so thin, that the weight of the spheres was less than an equal volume of water, they would have floated.)

As the spheres sank, the pressure of water got greater and greater. In air, the air pressure comes from the weight of the air above you. When you are under water, the pressure is the pressure of the air (pushing on the surface of the water) increased by the weight of the water. If you dive 30 feet, the pressure is twice that of the air at the surface.

Ewing designed the spheres to be strong enough to withstand the pressure of water down to a depth of 1000 meters. But at that depth, the pressure finally was too much, and the spheres were suddenly crushed. (Like an egg, the round surface provides lots of strength, but when it breaks, it breaks suddenly.) The water and metal collapse, and bang against the material coming in from the other side. It's like a hammer hitting a hammer, and it generates a loud sound. The energy released from a sphere with radius 1-inch at a depth of 1 km, is approximately the same as in 60 milligrams of TNT.  That doesn't sound like a lot -- but it is about the same you might find in a very large firecracker.

In the air, the sound of a firecracker doesn't go far, perhaps a few kilometers.  But the sound channel is quiet.  Only sounds generated in the sound channel itself are carried.  So microphones placed within the sound channel can hear sounds that come from thousands of kilometers away.

The Navy had arranged for several such microphones placed at important locations, where they could pick up the ping of the imploding Ewing spheres.  They could locate where the implosion had taken place by the time of arrival of the sound.  If the sound arrived simultaneously at two microphones (for example), then they knew the sound had been generated somewhere on a line that is equally distant from the two microphones.  With another set of microphones they could draw another line, and the intersection of the two lines gave the location of the downed pilot.

Historical note: I learned about the Sofar spheres from Luis Alvarez, who knew about them from his scientific work during World War II. I have spoken to several other people who remember them, including Walter Munk and Robert C. Spindel. Spindel believes that the spheres contained a small explosive charge to enhance the sound. We have not yet found any historical documentation for these questions.

The sound channel -- and whale songs

What does the sound channel look like? The word "channel" can be misleading, since it brings up a vision of a narrow corridor. It is not like a tube. It is a flat layer, existing about a kilometer deep, spreading over most of the ocean. Sound that is emitted in the sound channel tends to stay in the sound channel. It still spreads out, but not nearly as much as it would if it also spread vertically. That's why it can be heard so far. It tends to get focused and trapped in that sheet.

In fact, the sound channel is like one floor in a very large building, with ceiling and floor but without walls. Sound travels horizontally, but not vertically.

If sound is emitted at the surface of the ocean, then it does not get trapped. So the sound of waves and ships doesn't pollute the sound channel. The sound channel is a quiet place for listening to Sofar spheres, and other sounds that were generate in the sound channel.

Whales discovered this, probably millions of years ago. We now know that whales like to sing when they are at the sound channel depth. These songs are hauntingly beautiful. If your computer has the right software, you can listen here to the recorded song of the humpback whale and of the gray whale. You can find other recordings on the web, and you can buy recordings on CDs.

 

Global Positioning System (GPS)

A favorite gift for hikers, boaters, and travelers is a GPS receiver. This is a small device that will tell you where you are on the earth, to an accuracy of a few feet! You can buy one at a sporting goods store for about $100. If you rent a car, for a small charge you can get one with GPS built in -- to keep you from getting lost.

Why am I talking about GPS? Because GPS uses the same idea that Maurice Ewing used for locating pilots. For GPS, however, the signals are sent using radio waves rather than sound. And instead of using microphones set on the edges of the ocean, it uses radio receivers orbiting the Earth.

The GPS system works because there are a large number of satellites in space that are emitting signals. Each signal contains the time when it was emitted, and the position of the satellite when it was emitted. (How do you suppose the satellite knows this?) The GPS also has a small computer, and an accurate clock.

When the GPS receiver receives a signal, it looks at the time, reads the message saying when the signal was emitted, and determines how long the signal was traveling. It multiplies that by the speed of light, and that gives it the distance to the first satellite. Of course, it also knows exactly where that satellite was when it emitted the signal. Once the GPS knows its distance from three different satellites, it can use geometry to calculate where it is. Can you see why that works?

Geometry: How does the GPS system get its location by knowing the distance to three satellites? It's easy to see by analogy. Suppose you didn't know where you were in the US, but knew that you were 1000 miles from Denver, and 1500 miles from San Francisco. You could get a map, draw a circle around Denver with a 1000 mile radius; then draw a 1500 mile circle around San Francisco. The circles intersect at two points. If you knew your distance to one other city, you would know which of those two points was your location.

Interesting detail. If the GPS receiver gets a signal from four satellites, then it can see if the distance to that satellite is exactly what it expected. It should come out right -- since the GPS already knows its own position. Suppose it turns out to be wrong? The only explanation can be that the GPS clock has drifted and is no longer accurate. So the GPS can use the 4th satellite to fix its clock! The result is that if it can pick up 4 satellites, the receiver does not need an accurate clock.

The Cold War -- and SOSUS

During World War II, the part of the military that used submarines was called "The Silent Service." This reflected the fact that any sound emitted by a submarine could put it in danger, so submariners trained themselves to be very quiet. Someone in a sub who drops a wrench makes a sound that is unlike any other in the ocean. Fish don't drop wrenches. The wrench clatters against the hull, and the hull carries the sound to the water, and the vibrations of the hull send the sound into the ocean. Ships on the surface, and other submarines, had sensitive microphones to listen to possible sounds emitted from submarines.

The presence of the sound channel did not remain secret for long, but its properties did. In the period from the 1950s to 1990s, the United States spent billions of dollars to put hundreds of microphones into the channel at locations all around the world, to carry the signals back to an analysis center, and then use the world's best computers to analyze them. The system was called SOSUS, an acronym for "SOund SUrveillance System." The magnitude of the SOSUS effort was one of the best-kept secrets of the Cold War. Effective use of SOSUS required the Navy to make extensive measurements of the ocean and its properties, and to update the temperature profile of the ocean all around the world. (The ocean has weather fronts analogous to those in the atmosphere.)

Book to read (optional). If you really want to know more about this subject, one of the best introductions is the novel "The Hunt for Red October" by Tom Clancy. When this novel came out in 1984, much of the material in it was still classified. Clancy had a talent for reading documents, talking to people, and figuring out from what they said, what was really true. The book was so detailed, and so accurate (it does have some fiction in it too -- and some things that he got wrong) that new people joining the Submarine service were told to read the book in order to get a good picture of how operations worked! Many of the details of the SOSUS system were finally declassified in 1991, seven years after Clancy's book was published.

Sound -- doesn't always travel straight

The magic of the sound channel is that sound always bends towards it. So if sound is rising above the channel, it bends downwards back into it. If it passes through and goes below, then it tends to bend upwards. Why is this?

The reason is that waves always tend to bend towards a region where they travel slower. To understand why this is so, imagine that you are walking arm in arm with a friend. If your friend is on your left side, and slows down, that pulls your left side backwards, and turns you towards the left. If your friend speeds up, that pulls your left arm forward, and turns you to the right (and also turns your friend to the right). The same phenomena happens with waves.

Remember it this way: Waves tend to change their direction towards the side that has a slower wave velocity.

EXAMPLES

Sound during the day. At high altitude, the air is usually colder. Imagine a sound wave that is initially traveling horizontally, near the surface of the earth. Above it, the velocity is lower, so it will tend to bend upward. This is shown in the following diagram.

The sound bends away from the ground.

Sound in the evening. When the sun sets, the ground cools off rapidly. (It does this by emitting infrared radiation; we'll discuss this further in the chapter on "invisible light".) The air does not cool so quickly, so in the evening, the air near the ground is often cooler than it is up higher. This phenomena is called a "temperature inversion." Sound tends to bend down towards the ground, as shown in the figure below.

Sound during the day, again. Now let's look at the morning situation again, with warm air near the ground, and cold air up high. But let's draw many sound paths, all coming from the same point. This is done in the diagram below.

The solid line at the bottom represents the ground. Note that it blocks certain paths -- the ones that drop too steeply. In the lower right corner is a small region that none of the paths can reach, since to reach this region the sound waves would have to go through the ground. (We'll assume for now that the ground absorbs or reflects sound, and does not transmit it, at least, not very well.) If the sound were coming from the point on the left, and you were standing in the shadow zone, then you wouldn't hear any sound at all. You are in the sound shadow of the ground!

This diagram shows why mornings tend to be quiet. Sounds bend up towards the sky, and if you are near the ground, there is no way that most of them can reach you.

Sound in the evening, again. In the diagram below, I've redrawn the evening situation, with the inverted temperature profile (cold at the bottom, warm at the top).

Note that there is no shadow zone. No matter where you stand, there are paths by which the sound can reach you.

Have you ever noticed that you can hear more distant sounds in the evening than in the morning? I've noticed that in the evening I can often hear the sound of distant traffic, or of a train; I rarely hear such sounds in the morning. (This phenomenon first mystified me when I was a teenager, living 1/4 mile from the beach. I noticed that I could hear the waves breaking in the evening, but almost never in the morning.

The explanation is in the diagrams above: in the morning there is a shadow zone for most sound, and if I am near the ground, then many sounds can't reach me; they are bent up to the sky.

An exception: predicting a hot day. There are times when I wake up in the morning and hear distant traffic. Then I know that it will probably be a hot (and maybe smoggy) day. Why?

The reason is that hearing distant sounds means there is an inversion, i.e. the high air is warmer than the low air. The presence of an inversion in the morning leads to a special weather condition, because it means that as the air near the ground warms, it will not rise. Normally, hot air rises into cold air, since hot air is less dense. But if there is hot air above, that kind of convection doesn't take place. With no place to rise to, the hot air accumulates near the ground, making for a hot day. Smog and other pollutants also accumulate. The weather forecast on the radio or TV will often announce that there is an "inversion". Now you know what that means.

Focusing sound: the sound channel explained

In the ocean, the temperature of the water gets cooler as we go further down. This would make the speed of sound less. But, as mentioned earlier, the water is also getting more and more compressed (i.e. denser) because of the increasing pressure. This tends to make sound go faster. When these two effects are combined, we get a gradual decrease in sound velocity as we go from the surface to about 1 km depth, and then the sound velocity increases again. This is illustrated in the diagram below. Darker means slower sound (just as it did in the atmosphere diagrams).

I've also drawn the path of a ray of sound. Notice that it always bends towards the slow region. The path I drew started with an upward tilt, was bent downward, passed through the slow region, and then was bent upward. The path oscillates up and down, but never gets very far from the slow region, the 1 km-deep "sound channel".

Exercise: Draw some other paths, starting at different angles. What happens if the ray starts out horizontally? Vertically?

Back to UFOs: a sound channel in the atmosphere?

Soon after he did his work in the ocean, Maurice Ewing realized that there would be a sound channel in the atmosphere! His reasoning was simple: as you go higher, everyone knows the air gets colder. Mountain air is colder than sea level air. The temperature of the air drops about 4 degrees Fahrenheit for every 1000 feet of altitude gain.

That means that the velocity of sound decreases with altitude. But he also knew that when you get to extremly high altitudes, the temperature begins to rise again. Starting at about 40-50,000 ft, the air starts getting warmer. This is shown in the following figure:

That means that the speed of sound is fast at both high and low altitudes, and slower at about 50,000 ft.

Look at the diagram above the previous one, the diagram that showed sound moving in a wiggly line through the ocean. Exactly the same diagram can be used for sound in the atmosphere! There is a sound channel centered at about 50,000 feet. (The exact altitude depends on latitude, as well as on the season of the year.)

Ozone: the cause of the high altitude heating. Why does the air get warm at very high altitude? The reason is the famous ozone layer. At about 40-50,000 feet, there is an excess of ozone, and this ozone absorbs much of the ultraviolet radiation from the sun. (Ultraviolet is that part of sunlight that is more violet than violet. This light is there, but invisible to the human eye. The ozone layer protects us, since ultraviolet light when absorbed on the skin can induce cancer.

Why is the ozone layer famous? At the end of the 20th century, scientists began to fear that the ozone layer could be destroyed by human activity, and that would let the cancer-causing ultraviolet radiation reach the ground with greater intensity. In particular, they worried about the release of certain chemicals into the atmosphere (CFCs, an abbreviation for "chloro-fluoro-carbons", a chemical used in refrigerators and air conditioners). CFCs release fluorine, and fluorine catalyzes the conversion of ozone O3 into ordinary O2|. (To balance the equation, 2 molecules of O3 turn into 3 molecules of O2.) The use of CFCs was outlawed internationally, and this is expected to solve the problem.

Looking at the ozone layer (and the sound channel): thunderhead tops. On a day where there are large thunderstorms, you can see where the ozone layer is: right at the top of the tallest thunderheads. A thunderstorm grows from hot air at the ground, rising up through the colder (and denser) air above it. When the warm air hits the warm air of the ozone layer, it no longer rises. The cloud spreads out, making the "anvil head" shape that people associate with the biggest storms. So when you see the flat top of a large thunderhead cloud, you are looking at the ozone layer, and at the middle of the sound channel.

Project Mogul and the "flying disks"

Maurice Ewing had an urgent application for his predicted atmospheric sound channel: the detection of nuclear tests in Russia. In the late 1940s, the "Cold War" had begun, and there was growing fear of the totalitarian communism represented by Russia. They had great scientists, and there was widespread belief that they would be building an atomic bomb soon. At that time, Russia was a very secret and closed society. (In fact, Stalin was starving 30 million "Kulak" farmers, and he could get away with it because he controlled information going in and out. In 1948, George Orwell wrote "1984". You might enjoy my essay "1989 was 1984".)

Ewing realized that as the fireball from a nuclear explosion rose through the sound channel, it would generate a great deal of noise that would travel around the world in the channel. He argued that we should send microphones up into the sound channel to detect and measure any such sound. The microphones that he used were called "disk microphones". You can see them in photographs of old radio shows. Click for an old photo of a disk microphone. There is also a photograph of a somewhat smaller disk microphone used by Orson Wells in his famous 1938 broadcast of the "War of the Worlds", when he actually convinced many listeners that the world was under attack by Martians!

Ewing's idea was to string the microphones under a high-altitude balloon, have them pick up the sounds in the sound channel, and radio them back to the ground. The disk microphones were called "flying disks." (The word flying was not confined to airplanes; it was equally used by ballooners when they went up.) The balloons were huge, and the string of microphones was 657 feet long, longer than the Washington Monument is high: see the diagram of Project Mogul and the Eiffel Tower.

The project was a success. The system detected American nuclear explosions, and then, on August 29, 1949, it detected the first Russian test.

The Roswell crash of 1947

One of the Project Mogul balloon flights crashed near the Roswell Army Air Force base on July 7, 1947. It was recovered by the Army, who issued a press release stating that "flying disks had been recovered." The Roswell Daily Record had headlines the next day: RAAF Captures Flying Saucer.

It was not a flying saucer; it was a complex balloon project that carried flying disks -- microphones to pick up Russian nuclear explosions. The program was highly classified, and the press release said more than the security people considered acceptable, so the next day the press release was "retracted." A new press release stated that what had crashed was a "weather balloon." It wasn't a weather balloon. The US Government was lying.

discussion question: should the US Government ever lie? This is just the sort of issue that you should confront before you become president!

The government tells the truth. In 1994, at the request of a congressman, the U.S. government declassified the information they had on the Roswell incident, and prepared a report

Documents available for you to read are:

Of these articles, you should read at least the New York Times article. The Popular Science articles give interesting background. The Official US Government report gives details that some of you might find interesting.

How do we know the government isn't lying now? Many people believe the official government report on Project Mogul is just an elaborate cover-up. They believe that a flying saucer really did crash, and the government doesn't want the public to know. Maybe I am part of this conspiracy, and part of my job is to mislead you into believing that flying saucers don't exist! (According to the movie "Men in Black", the job of the Men in Black is to make sure the public never finds out.)

I suggest the following answer: the people who continue to believe that Project Mogul never happened, probably don't understand the remarkable science of the ocean and atmosphere sound channels. I could not have invented such a wonderful story. It has too many amazing details. In contrast, it is relatively easy to make up stories about flying saucers. Those don't require much imagination. So here is my hypothesis: it is possible to distinguish the truth by the fact that it is more fascinating!

Of course, I might be lying.