Radar in the Modern World
Radar is usually taken for granted in these days of modern technology. Many people do not know how radar is really used, how it works, or why we need it. People are familiar with several uses of radar like police enforcement radar guns and radar that measures how fast a baseball is pitched in a major league game. These are only a few of the many uses radar has to offer. Radar can determine several properties of an object from a distance, such as its position, speed, direction of travel, and shape; it can also detect objects out of the range of sight in all weather conditions, making it a fundamental utility for many industries.
The term radar actually came from the acronym representing RAdio Detection And Ranging. Radar is a detection system used to locate and identify objects. Simply put, radar is the process in which radio waves are emitted from the source of the system; those waves ricochet off objects in their path, and the radar system detects the echoes of signals that return.
“One would think that so important a contribution to the world’s technology would be chronicled with great care at every stepThis, unfortunately, is not the case, and for reasons quite understandable” (Page 14). Sometimes history can be hard to distinguish from truth and legend, the history of radar is no exception. Many contributions have been made to the development of radar over the years. For many years prior and during the Second World War, radar was considered a top-secret military tool. Once it was made public, people used the existing information about radar to come up with their own variations for different applications. As a result, the true origin of radar has become blurred within conflicting claims.
Radar can be traced back as far as 1832 when British physicist Michael Faraday suggested the existence of an electromagnetic field between certain objects from his scientific observations. Working from these ideas, British physicist James Clerk Maxwell predicted mathematically the existence and behavior of radio waves in 1873. In 1886, physicist Heinrich Hertz from Germany and Elihu Thomson from America confirmed the existence of radio waves with demonstrations showing examples of reflection, refraction, and direction finding of radio waves. By 1904, Christian Hulsmeyer, a German inventor, applied for a patent for a device that used radio waves in a collision-avoidance device for ships. Hulsmeyer’s system was not very accurate and only signaled when two ships’ radio waves were in concurrent directions, which meant that they were headed directly for each other; however, it was only effective for a range of one mile. His detection device worked off the ship’s existing low-frequency radios which did not travel very far. In June of 1922, Italian radio expert, Guglielmo Marconi drew attention to the fact that he had observed the reflection of high-frequency waves by metallic objects many miles away (Page 183); soon after this discovery, many people from around the world began developing devices to use this discovery for navigation purposes .
The first true discovery of radar was in September of 1922 when Americans Albert H. Taylor and Leo C. Young observed the interruption of high frequency radio communication by ship passing between transmitter and receiver. They also observed “beats” produced by large objects when they moved within the transmission area (between the source and receiver). Taylor and Young named it the beat method for a reason. While working with a high frequency radio communication from opposing sides of a river in New York, the normal steady tone that they were working on suddenly grew twice in loudness then faded into nothing. A short time after, the tone grew back to twice its original loudness, and then back down to its original decibel level. In curiosity, the men looked out to see that a large steam boat had just passed through their line of radio signal causing the gap in radio contact. Since both men were employed by the U.S. Navy, they knew the difficulties the navy had with guarding a harbor in low visibility (Page 21). At that moment, the first practical use of radar was born.
Radar was still in its infancy, but ideas were showing up everywhere. In 1930, Young and Lawrence A. Hyland were studying at the U.S. Naval Research Laboratory, experimenting with a short-wave transmitter and receiver over several miles. The receiver started to pick up unusual reception, and the tone fluctuated up and down. Looking for what was wrong, Hyland checked and rechecked all the possibilities. Finally, he discovered that at every instance the mysterious action took place, an airplane was flying overhead. With this new discovery, radar became a known science, and the military set up a formalized project titled Detection of Enemy Vessels and Aircraft by Radio (Page 26). These two discoveries by Young, Taylor, and Hyland were crucial in the development of the original form of radar. Without these discoveries, there would be no radar.
In 1925, Gregory Breit and Merle A. Tuve, two research workers from Carnegie Institution of Washington, performed many ionosphere experiments, the technique used in modern day radar (Shafford). Ionization is the formation of electrically charged atoms or molecules; initially, atoms posses a neutral charge and when an atom loses a negatively charged electron for one reason or another, it becomes a positively charged ion.
The ionosphere is a layer of ions in the atmosphere approximately 50 miles above the earth’s surface extending up to 600 miles or more above the Earth. At these altitudes, the air is extremely thin allowing air particles to spread out. When the atmospheric particles are ionized by radiation, usually by the ultraviolet rays from the sun, they tend to remain ionized, because few molecular collisions occur in the upper atmosphere which would change them back to non-charged molecules. Most molecules at these extreme altitudes are ions making a layer of charged particles allowing the gas to become a conductor of electricity.
Using this charged layer, scientists could rebound radio waves off the reflective layer. The ionosphere also curves with the earth; therefore, it was possible to bounce a wave off the ionosphere and beyond the horizon to the receiver. Without this discovery, people would not know the possibilities of sending radio signals beyond the horizon because electromagnetic waves travel in a straight line to infinity until it meets an object obstructing its path. That object in this instance is the ionosphere.
It is important to remember when a transmitter sends out a signal, the echo returns. That return of the echo is the most important part of the process of locating remote objects. The receiver picks up radar because of pulses. The transmitter sends out pulse after pulse in even increments. When the returned pulses are received, the time is calculated to figure out the distance of a remote object. These timings are in microseconds since the waves travel at the speed of light. The development of pulse radar began on March 14, 1934 at the Naval Research Laboratory and continued on throughout WWII.
The ideas basic to radar are listed by Robert page who studied at the Naval Research Laboratory in Washington DC and held 37 patents in radar:
1) Electromagnetic radiation at high radio frequency be employed for the detection and location of remote objects, or “targets,”
2) Radiation is sent out in pulses not more than a very few microseconds in duration, separated by time intervals tens to thousands of times greater than the pulse duration,
3) Reflections of the short pulses scattered back from targets be received and displayed by a receiver in close proximity to the transmitter,
4) Distance to targets be determined by measuring the time of travel of pulses to the target and back, and
5) Direction to targets be determined by using highly directive antennas for transmitter, or for receiver, or for both. (37)
These basic ideas can be applied to any type of radar used today, and Page wrote this in 1962. Radar may involve intricate mathematics, but these principles describe the basic ideas of how radar works.
Most radar systems in use today use the Doppler Principle, named after the man who discovered its effects, Christian Doppler (1803-1853). He worked with different kinds of sound waves. A source of sound emits waves out into the environment; as the waves move out from the source, they spread out. As a source of sound travels past a fixed point, the frequency starts to condense as the source gets closer to the point, and it spreads out as it moves away from the point. It is for this reason that the siren on a fire truck seems to be increasingly higher pitched as it gets closer and increasingly lower pitched as it travels away; the firemen on the trucks do not hear a change in pitch because they are in the same location relative to the siren.
Radar relies heavily on the Doppler Principle. The electromagnetic pulses that the source sends out are much like the waves of sound except the pulses move at higher frequencies and faster speeds. The return of the waves is the most important part of the functionality of the radar system; the receiver picks up the returned waves and calculates the spacing between each wave giving the location of the object targeted. The exact process for triangulating the location of an object using electromagnetic waves requires complicated trigonometry and calculus equations that are difficult to comprehend.
The implications of radar are unimaginably diverse, from police enforcement for speed all the way to satellite imaging. One of the most common encounters with radar people deal with is police-issued radar guns. Law enforcement officers use radar in order to tell them how fast drivers are traveling. Police must aim the radar at a reflective surface, such as a piece of metal on a car, and the gun picks up the returning waves; the returned waves are measured and calculated internally using the Doppler Principle. Doppler radar is used in many ways, and the most common way people encounter is on the television.
The news at five o’clock always shows the weather predictions for the upcoming days. The meteorologist shows several images of the United States. What he/she shows are the weather movements. They can easily look up weather movements using satellite imaging and radar. This radar is called Doppler Radar; it uses electric pulses out into the atmosphere almost constantly. The radar that returns is from the raindrops within a cloud. They can create a digital picture of the cloud shape from the different lengths of the returned microwaves. Over time, the cloud(s) move, and the radar in conjunction with satellite imaging, which also uses radar, creates a picture on a computer screen in turn, showed on viewers’ home televisions. Viewers are now accustomed to seeing the forecasts with the radar-produced images.
Some consider radar the most useful tool in warfare. During World War II, both sides used radar as a fairly accurate indicator of location. Radar prevented the enemy from carrying out surprise aerial attacks. One thing that the radar could not yet perform is distinguish between friendly aircraft, enemy aircraft, or even a large flock of birds. The Japanese attack on Pearl Harbor on December 7, 1945 was a complete surprise on the Pacific fleet because the soldiers watching the radar saw the incoming aircraft and assumed it to be their own array of bombers returning early. Needless to say, radar has improved over the last 60 years.
Military today depends on radar for more information today then they ever did before. Radar can be in fixed positions, mobile units, or even satellites. The element of surprise is a great advantage in military tactics, and the removal of the surprise can be quite beneficial to the defender. Military uses radar for two main reasons: to constantly scan for enemies or to pinpoint potential targets. It is extremely effective in both applications.
Another effect radar has on the world is through the applications in aviation. Used all over the world in thousands of airports, radar has increased safety by an immeasurable degree. Depending on how large the airport may be, it could have its own radar system. Air traffic control uses radar to see aircrafts’ locations. Using the information about the location of the aircraft, the Air Traffic Control man/woman can direct the individual aircraft out of harm’s way. Several aircraft today, especially military, have display screens showing where other aircraft are. Even though they can see where the other aircraft is, the radar system is on the ground in a fixed point.
Truly understanding how radar works takes a lot of dedication to the subject. Calculus and trigonometry are involved with the processing of radar. Many people have dedicated their lives to further understanding radar because of their interests. Throughout the world, radar has countless uses ranging from measuring how fast pitchers can throw the ball during a baseball game, what the weather is going to be, how fast a car is going down a street, and to the extremes of pinpointing the position of enemy defense posts. Without radar, life would not be the same.
Britannica Concise Encyclopedia. 2004. Encyclopedia Britannica. 12 Oct. 2004 .
Brookner, Eli. Radar Technology. Dedham, Eng. Artech, 1977.
Cole, Henry W., Understanding RADAR. London: Collins, 1985.
CopRadar.com. 1999. 26 Oct. 2004 .
Freeman, Tony. “What Is Imaging Radar?” Jet Propulsion Laboratory-NASA. 26 Oct. 2004. .
Online Air Defense Radar Museum. Radomes Inc. 2003. 26 Oct 2004. .
Page, Robert Morris. The Origin of Radar. Garden City, NJ: Anchor, 1962.
Radar Meteorology. 1997. University of Illinois. 26 Oct. 2004 .
Shafford, A. Basic Radar. Knightsbridge: Modern UP, 1947.
Toomay, J.C. Radar Principles for the Non-Specialist. 2nd ed. Mendham, NJ: Scitech, 1998.