The Millstone Hill Steerable Antenna, or MISA, is a fully steerable

dish antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or par ...

, in diameter, designed by the

Stanford Research Institute SRI International (SRI) is an American nonprofit scientific research institute and organization headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as a center of innovation to support economic d ...

(SRI) in 1959. It is currently located at

MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...

Haystack Observatory 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 ...

in Westford, Massachusetts.

History

MISA was originally installed at the Sagamore Hill Radio Observatory in

Hamilton, Massachusetts Hamilton is a town in the eastern central portion of Essex County in eastern Massachusetts, United States. At the 2020 census, it had a population of 7,561. Currently the town has no manufacturing industry and no industrially-zoned land. Though ...

in 1963. The antenna operated at that location until 1978, at which time it was relocated to Millstone Hill. Since that time it has been primarily used as a UHF

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

antenna to provide measurements of the

near space The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define its limits: it ...

environment using the

incoherent scatter Incoherent scattering is a type of scattering phenomenon in physics. The term is most commonly used when referring to the scattering of an electromagnetic wave (usually light or radio frequency) by random fluctuations in a gas of particles (most o ...

radar technique. It is one of two surviving dish antennas of this type in the world with the other antenna being located at the

Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...

radio science field site in

Stanford, California Stanford is a census-designated place (CDP) in the northwest corner of Santa Clara County, California, United States. It is the home of Stanford University. The population was 21,150 at the United States Census, 2020, 2020 census. Stanford is ...

. MISA is used to provide wide radar coverage in latitude and longitude.

Capabilities

MISA is a broad-based observatory capable of addressing a wide range of

atmospheric science Atmospheric science is the study of the Atmosphere of Earth, Earth's atmosphere and its various inner-working physical processes. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climat ...

investigations. The incoherent scatter radar facility at Millstone Hill has been supported by the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...

since 1974 for studies of the Earth's

upper atmosphere Upper atmosphere is a collective term that refers to various layers of the atmosphere of the Earth above the troposphere and corresponding regions of the atmospheres of other planets, and includes: * The mesosphere, which on Earth lies between the ...

and

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to 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 ...

. During this time the facility has evolved from a part-time research operation sharing radar cooling and power supply elements with the M.I.T.

Lincoln Laboratory The MIT Lincoln Laboratory, located in Lexington, Massachusetts, is a United States Department of Defense federally funded research and development center chartered to apply advanced technology to problems of national security. Research and dev ...

Millstone satellite tracking radar, to a separately funded, operationally independent system dedicated to upper atmospheric research. The scientific capability of the Millstone Hill facility was greatly expanded in 1978 with the installation of a fully steerable 46 meter antenna to complement the 67 meter fixed

zenith The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" ...

pointing dish. The favorable location of Millstone Hill at sub-auroral latitudes combined with the great operational range afforded by the steerable antenna permit observations over a latitude span encompassing the region between the

polar cap Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

and the near-

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

ial ionosphere. Since 1982 the Haystack Observatory Atmospheric Sciences Group has been supported for operating the Millstone Hill research radar as a part of the incoherent scatter radar chain and for associated studies of the

auroral An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of br ...

and sub-auroral ionosphere and

thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...

. The meridional radar chain extends from Sondrestrom Upper Atmospheric Research Facility in

Kangerlussuaq Kangerlussuaq (; ; da, Søndre Strømfjord), is a settlement in western Greenland in the Qeqqata municipality located at the head of the fjord of the same name. It is Greenland's main air transport hub and the site of Greenland's largest commer ...

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

through Millstone Hill at mid-latitudes, beyond

Arecibo Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, th ...

at low latitudes, to the Jicamarca facility at the magnetic equator in

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

. The radar chain forms an integral part of the NSF-supported CEDAR ( Coupling, Energetics, and Dynamics of Atmospheric Regions) observing network and Millstone Hill observations and analysis have contributed extensively to the successes of the CEDAR initiative.

Scatter technique

The Millstone Hill Radar uses Thomson

backscatter In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, a ...

from ionospheric

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s to deduce height- and time-resolved plasma drift velocities, electron and ion temperatures, electron densities, ion composition, and ion-neutral collision frequencies. These parameters provide further information about the neutral gas, neutral temperatures and winds, and electric fields present in the medium. The incoherent scatter technique provides observations of many of these parameters over an altitude range extending from less than 100 km to a thousand kilometers or more. Methods have been developed that allow these measurements to be made with an altitude resolution of hundreds of meters. The complete steerability of the radar allows horizontal gradients and structure to be examined along with vertical variations.

References

{{reflist

External links

Millstone Hill Observatory
at

Radio telescopes