Related Research Articles
The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth.
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF bands. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.
Radar is a radiolocation system that uses radio waves to determine the distance (ranging), angle, and radial velocity of objects relative to the site. It is used to detect and track aircraft, ships, spacecraft, guided missiles, and motor vehicles, and map weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.
The High-frequency Active Auroral Research Program (HAARP) was initiated as an ionospheric research program jointly funded by the U.S. Air Force, the U.S. Navy, the University of Alaska Fairbanks, and the Defense Advanced Research Projects Agency (DARPA). It was designed and built by BAE Advanced Technologies. Its original purpose was to analyze the ionosphere and investigate the potential for developing ionospheric enhancement technology for radio communications and surveillance. Since 2015 it has been operated by the University of Alaska Fairbanks.
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 megahertz (MHz) and below. At 300 GHz, the corresponding wavelength is 1 mm ; at 30 Hz the corresponding wavelength is 10,000 kilometers. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.
A whistler is a very low frequency (VLF) electromagnetic (radio) wave generated by lightning. Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, with a maximum amplitude usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies, and can be converted to audio using a suitable receiver. They are produced by lightning strikes where the impulse travels along the Earth's magnetic field lines from one hemisphere to the other. They undergo dispersion of several kHz due to the slower velocity of the lower frequencies through the plasma environments of the ionosphere and magnetosphere. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.
Plasma diagnostics are a pool of methods, instruments, and experimental techniques used to measure properties of a plasma, such as plasma components' density, distribution function over energy (temperature), their spatial profiles and dynamics, which enable to derive plasma parameters.
Plasma stealth is a proposed process to use ionized gas (plasma) to reduce the radar cross-section (RCS) of an aircraft. Interactions between electromagnetic radiation and ionized gas have been extensively studied for many purposes, including concealing aircraft from radar as stealth technology. Various methods might plausibly be able to form a layer or cloud of plasma around a vehicle to deflect or absorb radar, from simpler electrostatic or radio frequency discharges to more complex laser discharges. It is theoretically possible to reduce RCS in this way, but it may be very difficult to do so in practice. Some Russian systems e.g. the 3M22 Zircon (SS-N-33) and Kh-47M2 Kinzhal missiles have been reported to make use of plasma stealth.
EISCAT operates three incoherent scatter radar systems in Northern Scandinavia and Svalbard. The facilities are used to study the interaction between the Sun and the Earth as revealed by disturbances in the ionosphere and magnetosphere.
Polar mesospheric summer echoes (PMSE) is the phenomenon of anomalous radar echoes found between 80 and 90 km in altitude from May through early August in the Arctic, and from November through to February in the Antarctic. These strong radar echoes are associated with the extremely cold temperatures that occur above continental Antarctica during the summer. Rocket and radar measurements indicate that a partial reflection from a multitude of ion layers and constructive interference causes at least some of the PMSE.
The Madison Symmetric Torus (MST) is a reversed field pinch (RFP) physics experiment with applications to both fusion energy research and astrophysical plasmas.
Haystack Observatory is a multidisciplinary radio science center, ionospheric observatory, and astronomical microwave observatory owned by Massachusetts Institute of Technology (MIT). It is located in Westford, Massachusetts (US), approximately 45 kilometers (28 mi) northwest of Boston. Haystack was initially built by MIT's Lincoln Laboratory for the United States Air Force and was known as Haystack Microwave Research Facility. Construction began in 1960, and the antenna began operating in 1964. In 1970 the facility was transferred to MIT, which then formed the Northeast Radio Observatory Corporation (NEROC) with a number of other universities to operate the site as the Haystack Observatory. As of January 2012, a total of nine institutions participated in NEROC.
An ionospheric heater, or an ionospheric HF pump facility, is a powerful radio wave transmitter with an array of antennas which is used for research of plasma turbulence, the ionosphere and upper atmosphere. These transmitters operate in the high frequency (HF) range (3-30 MHz) at which radio waves are reflected from the ionosphere back to the ground. With such facilities a range of plasma turbulence phenomena can be excited in a semi-controlled fashion from the ground, during conditions when the ionosphere is naturally quiet and not perturbed by for example aurora. This stimulus-response type of research complements passive observations of naturally excited phenomena to learn about the ionosphere and upper atmosphere.
Tor Hagfors was a Norwegian scientist, radio astronomer, radar expert and a pioneer in the studies of the interactions between electromagnetic waves and plasma. In the early 1960s he was one of a handful of pioneering theorists that independently developed a theory that explained the scattering of radio waves by the free electrons in a plasma and applied the result to the ionosphere. He became founding director of the new EISCAT facilities that were then under construction in 1975, by which time he already been director at most of the other incoherent scatter radar facilities in the world. The asteroid 1985 VD1 is named 7279 Hagfors after him.
This is an index to articles about terms used in discussion of radio propagation.
The Jicamarca Radio Observatory (JRO) is the equatorial anchor of the Western Hemisphere chain of Incoherent Scatter Radar (ISR) observatories extending from Lima, Peru to Søndre Strømfjord, Greenland. JRO is the premier scientific facility in the world for studying the equatorial ionosphere. The observatory is about half an hour drive inland (east) from Lima and 10 km from the Central Highway. The magnetic dip angle is about 1°, and varies slightly with altitude and year. The radar can accurately determine the direction of the Earth's magnetic field (B) and can be pointed perpendicular to B at altitudes throughout the ionosphere. The study of the equatorial ionosphere is rapidly becoming a mature field due, in large part, to the contributions made by JRO in radio science.
The Millstone Hill Steerable Antenna, or MISA, is a fully steerable dish antenna, 46 metres (151 ft) in diameter, designed by the Stanford Research Institute (SRI) in 1959. It is currently located at MIT Haystack Observatory in Westford, Massachusetts.
The index of physics articles is split into multiple pages due to its size.
The Farley–Buneman instability, or FB instability, is a microscopic plasma instability named after Donald T. Farley and Oscar Buneman. It is similar to the ionospheric Rayleigh-Taylor instability.
Dynamics Explorer 2 was a NASA low-altitude mission, launched on 3 August 1981. It consisted of two satellites, DE-1 and DE-2, whose purpose was to investigate the interactions between plasmas in the magnetosphere and those in the ionosphere. The two satellites were launched together into polar coplanar orbits, which allowed them to simultaneously observe the upper and lower parts of the atmosphere.
References
- ↑ Gordon, W. (Nov 1958). "Incoherent Scattering of Radio Waves by Free Electrons with Applications to Space Exploration by Radar". Proceedings of the IRE . 46 (11): 1824–1829. doi:10.1109/JRPROC.1958.286852. S2CID 51635092.
- ↑ "Geospace".
