MPH PYTHON III, Руководство оператора

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15
General Operational Considerations
Understanding traffic radar
A historical perspective
The development of RADAR (an acronym for Radio Detection and Ranging) cannot be attributed
to a single inventor or even an identifiable group of inventors. It’s basic concepts have been
understood as long as those of electromagnetic waves have. As long ago as 1886, it was known
that radio waves could be reflected from solid objects. Although use of a radio echo for detection
purposes was discussed for many years in the literature, it took the imminent threat of war in
Europe in the late 1930's to bring about serious research and development.
The original purpose of radar was to provide advance warning of approaching enemy aircraft.
Consequently, a technique of transmitting radio waves and listening for the reflection was
developed in Germany, Great Britain, and the U.S. almost simultaneously. This search and
detection system measured the length of time it took for a reflection to come back, and from that,
distance could be calculated. Using this technique, many familiar devices were developed during
the war years, often under great secrecy. These include aircraft and ship navigation, the aircraft
altimeter, and radar mapping.
With the lifting of military security restrictions in 1946, the level of research in radar declined and
attention was turned to the development of civilian applications such as radio astronomy and
weather radar. Although a method of velocity measurement using a theory of physics called the
Doppler principle was well known, it was never applied to a radar until this post-war period. One
of the first applications in 1948 was in primitive traffic radar to measure the speed of autos. While
these early units were an improvement over the time distance stopwatch technique, they were
bulky, difficult to operate and suffered from certain technical limitations. It was more than twenty
years before a significant breakthrough was made to enable the development of the modern-day
radar as we now know it.
The Doppler Principle
As we have seen, a wide variety of radar devices have been developed over the years to perform
an even wider variety of tasks. Let us turn our attention to how this technology is being applied to
velocity measurement.
In 1842, an Austrian physicist and mathematician by the name of Christian Johann Doppler
postulated a theory that connects the frequency of a wave with the relative motion between the
source of the wave and the observer. This today is known as the Doppler principle and is used to
determine the velocity of everything from a pitched baseball to the largest galaxies in space.