Geoscience Reference
In-Depth Information
5.1
Introduction
Starting with a brief historical summary of the radar genesis, the radar operating
principles are discussed. Next in Sect. 5.4 , the two radars, which are investigating
Mars surface, subsurface, and atmosphere, are described, including a discussion
about the different capabilities of the two radars in terms of surface depth pene-
tration, subsurface detection, and resolution, along with the space missions they are
part of. Their main scientific accomplishments are described in Sect. 5.5 . Section 5.6
provides a brief presentation of a radar involved in a new coming space mission.
The term radar, currently part of the vocabulary of many languages as a
common noun, is the acronym for RAdio Detection And Ranging. It is an object-
detection system which uses radio waves in order to determine the range, altitude,
direction, or speed of objects. Its uses are very versatile; it can be used to detect
aircraft, ships, vehicles, missiles, spacecrafts, and weather formations. Its working
principle, described more in detail in Sect. 5.3 , is based on the transmission of
pulses of radio waves or microwaves through a dish or an antenna. When the
waves encounter an object (usually called target), a part of the wave energy gets
reflected and received by a dish or an antenna usually located at the same site as the
transmitter.
5.2
Early Radar History
The history of radar is highly linked to the history of electromagnetism, and it does
not have a well-defined origin because the vicissitudes that led to its creation and
use in the military and then civil fields have followed different paths in different
countries.
In 1886, German physicist Heinrich Hertz showed that radio waves could
be reflected from solid objects. In 1904, German engineer Christian Hülsmeyer,
through experiments on the detection of electromagnetic waves reflected from
ships, developed and patented an apparatus capable of detecting the presence of
distant metallic obstacles thanks to returning echoes. The apparatus, referred to as
“telemobiloskop,” was tested as an anticollision device and can be considered the
true forerunner of the modern radar.
The telemobiloskop was publicly presented in Cologne on 18th May 1904. The
system was composed of a directional antenna, a receiver, and a coherer transmitter.
The device allowed the detection of a metal object in a certain direction with a
range of about 3 km, without specifying the distance, and operated with 40 50 cm
wavelength waves. This device could work even in adverse weather conditions,
demonstrating the feasibility of detecting a ship in dense fog, and was judged
favorably by the press, but it did not arouse the interest of naval authorities nor
industry, and it was not put into production.
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