He graduated from University College, Dundee, in and then worked as an assistant for Professor William Peddie, who encouraged his fascination with radio waves.
In , Watson-Watt hoped to go to work for the War Office, but no suitable position in communications was available there, so he joined the Meteorological Office. He was put to work developing systems for detecting thunderstorms. Lightning ionizes the air and generates a radio signal, which Watson-Watt could detect to map the positions of thunderstorms.
The Air Ministry had already offered pounds to anyone who could demonstrate a ray that could kill a sheep yards away. In February Watson-Watt demonstrated to an Air Ministry committee the first practical radio system for detecting aircraft. The Air Ministry was impressed, and in April Watson-Watt received a patent for the system and funding for further development. Soon Watson-Watt was using pulsed radio waves to detect airplanes up to 80 miles away.
These stations, known as Chain Home, successfully alerted the Royal Air Force to approaching enemy bombers, and helped defend Britain against the German Luftwaffe in the Battle of Britain.
The Chain Home system worked fairly well, but it required huge antennas, and used long wavelengths that limited ability to pinpoint enemy aircraft accurately. During the day, fighter pilots could see enemy bombers. But soon the Germans began nighttime bombing missions, so to help fighter pilots locate enemy aircraft at night, the British needed a shorter wavelength radar system that was compact enough to install in planes. This became possible when British engineers Harry Boot and John Randall invented the cavity magnetron in early The magnetron generated about hundred watts of power at wavelengths about 10 centimeters, enough to produce echoes from airplanes many miles away.
They based their new research on radio and electronics experiments that started in the early 20th century. Inventors like Telsa, Butement and Pollard had been working with radio and pulsed modulation to detect ships and other metal objects, which did not attract much interest prior to World War II. The British and Americans were not the only ones experimenting with radio waves.
With tensions in Europe increasing in the mids, interest was renewed in these experiments. Scottish scientist, Robert Watson-Watt, was one of the participants and was a pioneering force behind the British use of radar. Watson-Watt and several other scientists helped created the Chain Home system, an early warning system on the English Channel, which would become instrumental in British defense during the Second World War.
Post war, work on radar technology slowed somewhat. There was a revival in the ss, and now radar systems and technology are used in thousands of ways in modern society. Bay devised a process he called cumulation, which is known today as integration. His integrating device consisted of ten coulometers, in which electric currents broke down a watery solution and released hydrogen gas.
The amount of gas released was directly proportional to the quantity of electric current. The coulometers were connected to the output of the radar receiver through a rotating switch. The radar echoes were expected [ 11 ] to return from the Moon in less than three seconds, so the rotating switch made a sweep of the ten coulometers every three seconds. The release of hydrogen gas left a record of both the echo signal and the receiver noise.
As the number of signal echoes and sweeps of the coulometers added up, the signal-to-noise ratio improved. By increasing the total number of signal echoes, Bay believed that any signal could be raised above noise level and made observable, regardless of its amplitude and the value of the signal-to-noise ratio. Despite the conceptual breakthrough of the coulometer integrator, the construction and testing of the apparatus remained to be carried out.
The menace of air raids drove the Tungsram research laboratory into the countryside in the fall of The subsequent siege of Budapest twice interrupted the work of Bay and his team until March The Ministry of Defense furnished Bay with war surplus parts for a 2. Work was again interrupted when the laboratory was dismantled and all equipment, including that for the lunar radar experiment, was carried off to the Soviet Union.
For a third time, construction of entirely new equipment started in the workshops of the Tungsram Research Laboratory, beginning August and ending January Figure 2. Courtesy of Mrs. Julia Bay. Electrical disturbances in the Tungsram plant were so great that measurements and tuning had to be done in the late afternoon or at night. The experiments were carried out on 6 February and 8 May at night by a pair of researchers.
Without the handicap of operating in a war zone, Bay probably would have beaten the Signal Corps to the Moon, although he could not have been aware of DeWitt's experiment. More importantly, though, he invented the technique of [ 12 ] long-time integration generally used in radar astronomy. As the American radio astronomers Alex G. Smith and Thomas D. Carr wrote some years later: "The additional tremendous increase in sensitivity necessary to obtain radar echoes from Venus has been attained largely through the use of long-time integration techniques for detecting periodic signals that are far below the background noise level.
The unique method devised by Bay in his pioneer lunar radar investigations is an example of such a technique. Each man engaged in other projects shortly after completing his experiment. Bay left Hungary for the United States, where he taught at George Washington University and worked for the National Bureau of Standards, while DeWitt re-entered radio broadcasting and pursued his interest in astronomy.
As an ongoing scientific activity, radar astronomy did not begin with the spectacular and singular experiments of DeWitt and Bay, but with an interest in meteors shared by researchers in Britain, Canada, and the United States.
Big Science, that is, ionospheric physics and secure military communications, largely motivated that research. Moreover, just as the availability of captured V-2 parts made possible rocket-based ionospheric research after the war, 29 so war-surplus radars facilitated the emergence of radar astronomy.
Like the exploration of the ionosphere with rockets, radar astronomy was driven by the availability of technology. Radar meteor studies, like much of radar history, grew out of ionospheric research. In the s, ionospheric researchers became interested in meteors when it was hypothesized that the trail of electrons and ions left behind by falling meteors caused fluctuations in the density of the ionosphere.
They concluded that meteors caused abnormal bursts of ionization as they passed through the ionosphere. During the war, the military had investigated meteor trails with radar. When the Germans started bombarding London with V2 rockets, the Army's gun-laying radars were hastily pressed into service to detect the radar reflections from the rockets during their flight in order to give some warning of their arrival.
In many cases alarms were sounded, but no rockets were aloft. James S. Hey, a physicist with the Operational Research Group, was charged with investigating these mistaken sightings.
He believed that the false echoes probably originated in the ionosphere and might be associated with meteors. Hey began studying the impact of meteors on the ionosphere in October , using Army radar equipment at several locations until the end of the war.
Stewart electrical engineer , S. Parsons electrical and mechanical engineer , and J. Phillips mathematician , found a correlation between visual sightings and radar echoes during the Giacobinid meteor shower of October Moreover, by using an improved photographic technique that better captured the echoes on the radar screen, they were able to determine the velocity of the meteors.
Neither Hey nor Appleton pursued their radar investigations of meteors. During the war, Hey had detected radio emissions from the Sun and the first discrete source of radio emission outside the solar system in the direction of Cygnus.
He left the Operational Research Group for the Royal Radar Establishment at Malvern, where he and his colleagues carried on research in radio astronomy. Appleton, by a Nobel Laureate and Secretary of the Department of Scientific and Industrial Research, also became thoroughly involved in the development of radio astronomy and became a member of the Radio Astronomy Committee of the Royal Astronomical Society in Instead, radar astronomy gained a foothold in Britain at the University of Manchester under A.
During the war, Lovell had been one of many scientists working on microwave radar. With the help of Hey and Parsons, Lovell borrowed some Army radar equipment. Finding too much interference in Manchester, he moved to the University's botanical research gardens, which became the Jodrell Bank Experimental Station. Lovell equipped the station with complete war-surplus radar systems, such as a 4. He purchased at rock-bottom prices or borrowed the radars from the Air Ministry, Army, and Navy, which were discarding the equipment down mine shafts.
Figure 3. The Jodrell Bank staff in front of the 4. Sir Bernard Lovell is in the center front. Originally, Lovell wanted to undertake research on cosmic rays, which had been Blackett's interest, too. One of the primary research objectives of the Jodrell Bank facility, as well as one of the fundamental reasons for its founding, was cosmic ray research. Indeed, the interest in cosmic ray research also lay behind the design and construction of the meter ft Jodrell Bank telescope.
The search for cosmic rays never succeeded, however; Blackett and Lovell had introduced a significant error into their initial calculations. Fortuitously, though, in the course of looking for cosmic rays, Lovell came to realize that they were receiving echoes from meteor ionization trails, and his small group of Jodrell Bank investigators began to concentrate on this more fertile line of research.
Nicolai Herlofson, a Norwegian meteorologist who had recently joined the Department of Physics, put Lovell in contact with the director of the Meteor Section of the British Astronomical Association, J. Manning Prentice, a lawyer and amateur astronomer with a passion for meteors. Also joining the Jodrell Bank team was John A.
Clegg, a physics teacher whom Lovell had known during the war. Clegg was a doctoral candidate at the University of Manchester and an expert in antenna design. He remained at Jodrell Bank until and eventually landed a position teaching physics in Nigeria. Clegg converted an Army searchlight into a radar antenna for studying meteors. When Prentice spotted a meteor, he shouted. His sightings usually, though not always, correlated with an echo on the radar screen.
Lovell thought that the radar echoes that did not correlate with Prentice's sightings might have been ionization trails created by cosmic ray showers. He did not believe, initially, that the radar might be detecting meteors too small to be seen by the human eye. The next opportunity for a radar study of meteors came on the night of 9 October , when the Earth crossed the orbit of the Giacobini-Zinner comet. Astronomers anticipated a spectacular meteor shower. A motion picture camera captured the radar echoes on film.
The shower peaked around 3 A. Lovell recalled that "the spectacle was memorable. It was like a great array of rockets coming towards one. The dramatic correlation of the echo rate with the meteors visible in the sky finally convinced Lovell and everyone else that the radar echoes came from meteor ionization trails, although it was equally obvious that many peculiarities needed to be investigated.
The Jodrell Bank researchers learned that the best results were obtained when the aerial was positioned at a right angle to the radiant, the point in the sky from which meteor showers appear to emanate. When the aerial was pointed at the radiant, the echoes on the cathode-ray tube disappeared almost completely.
Ellyett, followed in January by a Cambridge graduate, John G. Nicolai Herlofson developed a model of meteor trail ionization that Davies and Ellyett used to calculate meteor velocities based on the diffraction pattern produced during the formation of meteor trails. Clegg devised a radar technique for determining their radiant.
At this point, the Jodrell Bank investigators had powerful radar techniques for studying meteors that were unavailable elsewhere, particularly the ability to detect and study previously unknown and unobservable daytime meteor showers. Lovell and his colleagues now became aware of the dispute over the nature of meteors and decided to attempt its resolution with these techniques.
Astronomers specializing in meteors were concerned with the nature of sporadic meteors. One type of meteor enters the atmosphere from what appears to be a single point, the radiant. Most meteors, however, are not part of a shower, but appear to arrive irregularly from all directions and are called sporadic meteors. Most astronomers believed that sporadic meteors came from interstellar space; others argued that they were part of the solar system.
The debate could be resolved by determining the paths of sporadic meteors. If they followed parabolic or elliptical paths, they orbited the Sun; if their orbit were hyperbolic, they had an interstellar origin. The paths of sporadic meteors could be determined by an accurate measurement of both their velocities and radiants, but optical means were insufficiently precise to give unambiguous results.
Fred L. Whipple, future director of the [ 16 ] Harvard College Observatory, a leading center of United States meteor research, attempted state-of-the-art optical studies of meteors with the Super Schmidt camera, but the first one was not operational until May , at Las Cruces, New Mexico.
Radar astronomers, then, attempted to accomplish what optical methods had failed to achieve. Such has been the pattern of radar astronomy to the present. Between and , Lovell, Davies, and Mary Almond, a doctoral student, undertook a long series of sporadic meteor velocity measurements. They found no evidence for a significant hyperbolic velocity component; that is, there was no evidence for sporadic meteors coming from interstellar space.
They then extended their work to fainter and smaller meteors with similar results. The Jodrell Bank radar meteor studies determined unambiguously that meteors form part of the solar system. As Whipple declared in , "We may now accept as proven the fact that bodies moving in hyperbolic orbits about the sun play no important role in producing meteoric phenomena brighter than about the 8th effective magnitude.
The highly convincing evidence of the Jodrell Bank scientists was corroborated by Canadian radar research carried out by researchers of the Radio and Electrical Engineering Division of the National Research Council under Donald W.
McKinley conducted his meteor research with radars built around Ottawa in and as part of various National Research Council laboratories, such as the Flight Research Center at Arnprior Airport. Earle L. Webb, Radio and Electrical Engineering Division of the National Research Council, supervised the design, construction, and operation of the radar equipment. From as early as the summer of , the Canadian radar studies were undertaken jointly with Peter M.
Millman of the Dominion Observatory. They coordinated spectrographic, photographic, radar, and visual observations. The National Research Council investigators employed the Jodrell Bank technique to determine meteor velocities, a benefit of following in the footsteps of the British.
Their first radar observations took place during the Perseid shower of August , as the first radar station reached completion. Later studies collected data from the Geminid shower of December and the Lyrid shower of April , with more radar stations brought into play as they became available. Following the success of Jodrell Bank, [ 17 ] McKinley's group initiated their own study of sporadic meteors.
By , with data on 10, sporadic meteors, McKinley's group reached the same conclusion as their British colleagues: meteors were part of the solar system. Soon, radar techniques became an integral part of Canadian meteor research with the establishment in of the National Research Council Springhill Meteor Observatory outside Ottawa. The Observatory concentrated on scientific meteor research with radar, visual, photographic, and spectroscopic methods. These meteor studies at Jodrell Bank and the National Research Council, and only at those institutions, arose from the union of radar and astronomy; they were the beginnings of radar astronomy.
Radar studies of meteors were not limited to Jodrell Bank and the National Research Council, however. With support from the National Bureau of Standards, in Harvard College Observatory initiated a radar meteor project under the direction of Fred Whipple. Furthermore, radar continues today as an integral and vital part of worldwide meteor research. Its forte is the ability to determine orbits better than any other technique.
Unlike the Jodrell Bank and National Research Council cases, the radar meteor studies started in the United States in the early s were driven by civilian scientists doing ionospheric and communications research and by the military's desire for jam-proof, point-to-point secure communications. While various military laboratories undertook their own research programs, most of the civilian U.
The Stanford case is worth examining not only for its later connections to radar astronomy, but also for its pioneering radar study of the Sun that arose out of an interest in ionospheric and radio propagation research. In contrast to the Stanford work, many radar meteor experiments carried out in the United States in the s were unique events.
As early as August and November , for instance, workers in the Federal Communications Commission Engineering Department associated visual observations of meteors and radio bursts. On the night of 9 October , 21 Army radars were aimed toward the sky in order to observe any unusual phenomena.
The Signal Corps organized the experiment, which fit nicely with their mission of developing missile detection and ranging capabilities. For mainly meteorological reasons, only the Signal Corps SCR radar successfully detected meteor ionization trails. No attempt was made to correlate visual observations and radar echoes.
A Princeton University undergraduate, Francis B. Shaffer, who had received radar training in the Navy, analyzed photographs of the radar screen echoes at the Signal Corps laboratory in Belmar, New Jersey. This was the first attempt to utilize microwave radars to detect astronomical objects. In contrast to the Signal Corps experiment, radar meteor studies formed part of ongoing research at the National Bureau of Standards.
Organized from the Bureau's Radio Section in May and located at Sterling, Virginia, the Central Radio Propagation Laboratory CRPL division had three laboratories, one of which concerned itself exclusively with ionospheric research and radio propagation and was especially interested in the impact of meteors on the ionosphere. In October , Victor C.
Over the next five years, Pineo continued research on the effects of meteors on the ionosphere, using a standard ionospheric research instrument called an ionosonde and publishing his results in Science.
Pineo's interest was in ionospheric physics, not astronomy. His meteor work did not contribute to knowledge about the origin of meteors, as such work had in Britain and Canada, but it supported efforts to create secure military communications using meteor ionization trails. Frederick E. Terman, who had headed the Harvard Radio Research Laboratory and its radar countermeasures research during the war, "virtually organized radio and electronic engineering on the West Coast" as [ 19 ] Stanford Dean of Engineering, according to historian C.
Stewart Gillmor. Terman negotiated a contract with the three military services for the funding of a broad range of research, including the SRPL's long-standing ionospheric research program.
Villard, Jr. Villard had earned his engineering degree during the war for the design of an ionosphere sounder. As an amateur radio operator in Cambridge, Massachusetts, he had noted the interference caused by meteor ionizations at shortwave frequencies called Doppler whistles. Manning, and W. Evans, Jr. Manning then developed a method of measuring meteor velocities using the Doppler frequency shift of a continuous-wave signal reflected from the ionization trail.
Manning, Villard, and Allen M. Peterson then applied Manning's technique to a continuous-wave radio study of the Perseid meteor shower in August The initial Stanford technique was significantly different from that developed at Jodrell Bank; it relied on continuous-wave radio, rather than pulsed radar, echoes. One of those conducting meteor studies at Stanford was Von R.
Eshleman, a graduate student in electrical engineering who worked under both Manning and Villard. In , while returning from the war on the U. Missouri, Eshleman unsuccessfully attempted to bounce radar waves off the Moon using the ship's radar. Support for his graduate research at Stanford came through contracts between the University and both the Office of Naval Research and the Air Force. Eshleman's dissertation considered the theory of detecting meteor ionization trails and its application in actual experiments.
Unlike the British and Canadian meteor studies, the primary research interest of Eshleman, Manning, Villard, and the other Stanford investigators was information about the winds and turbulence in the upper atmosphere. Their investigations of meteor velocities, the length of ionized meteor trails, and the fading and polarization of meteor echoes were part of that larger research interest, while Eshleman's dissertation was an integral part of the meteor research program.
Eshleman also considered the use of meteor ionization trails for secure military communications. His dissertation did not explicitly state that application, which he took up after completing the thesis. The Air Force supported the Stanford meteor research mainly to use meteor ionization trails for secure, point-to-point communications. The Stanford meteor research thus served a variety of scientific and military purposes simultaneously.
Eshleman's dissertation has continued to provide the theoretical foundation of modern meteor burst communications, a communication mode that promises to function even after a nuclear holocaust has rendered useless all normal wireless communications. The pioneering work at Stanford, the National Bureau of Standards, and the Air Force Cambridge Research Laboratories received new attention in the s, when the Space Defense Initiative "Star Wars" revitalized interest in using meteor ionization trails for classified communications.
Non-military applications of meteor burst communications also have arisen in recent years. Early meteor burst communications research was not limited to Stanford and the National Bureau of Standards.
American military funding of early meteor burst communications research extended beyond its shores to Britain. Historians of Jodrell Bank radio astronomy and meteor radar research stated that radio astronomy had surpassed meteor studies at the observatory by However, that meteor work persisted until through a contract with the U.
Air Force, though as a cover for classified military research. Auroras provided additional radar targets in the s. A major initiator of radar auroral studies was Jodrell Bank. As early as August , while conducting meteor research, the Jodrell Bank scientists Lovell, Clegg, and Ellyett received echoes from an aurora display. Arnold Aspinall and G. Hawkins then continued the radar auroral studies at Jodrell Bank in collaboration with W. The problem with bouncing radar waves off an aurora was determining the reflecting point.
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