User:Marshallsumter/Radiation astronomy/Centimeters

For 10 cm radars, microwaves attenuation as used in weather radars absorbed by rain, is negligible.

Shorter wavelengths are useful for smaller particles, but the signal is more quickly attenuated; thus 10 cm (S-band) radar is preferred but is more expensive than a 5 cm C band system, but 3 cm X-band radar is used only for short-range units, and 1 cm Ka-band weather radar is used only for research on small-particle phenomena such as drizzle and fog.

Visuals
Cassini instruments provide complementary information about the structure of Saturn's rings. Narrow and wide angle cameras provide images in the visible region of the electromagnetic spectrum much like a digital camera does. The images have information about how the ring structure differs both with distance from the planet and with position around the equatorial circle. However, resolution is usually limited to few kilometers at best.

Radio and stellar occultations of the rings also provide important information about ring structure, but only along a one-dimensional track through the rings. The radial resolution can be as fine as 50 meters (164 feet). An "image" is then constructed by assuming circular symmetry over the ring region of interest. Color is usually added to encode other information related to the observed structure.

This image compares structure of Saturn's rings observed by these two approaches. The upper half is a natural color mosaic of images of the illuminated side of the rings by the Cassini narrow-angle camera (see PIA06175). The bottom simulated image is constructed from a radio occultation observation conducted on May 3, 2005. For another view created using this process, see PIA07872. Color in the lower image is used to represent information about ring particle sizes.

Three simultaneous radio signals of 0.94, 3.6, and 13 centimeter wavelength (Ka-, X-, and S-bands) were sent from Cassini through the rings to Earth. The observed change of each signal as Cassini moved behind the rings provided a profile of the distribution of ring material as a function of distance from Saturn, or an optical depth profile. This simulated image was constructed from the measured optical depth profiles.

Shades of purple, primarily over most of the middle ring, the B ring, and the inner portion of the outer ring, the A ring, indicate regions where there is a lack of particles less than 5 centimeters (about 2 inches) in diameter. Green and blue shades indicate regions where there are particles of sizes smaller than 5 centimeters (2 inches) and 1 centimeter (less than one third of an inch), respectively, primarily in the outer A ring and within most of the inner ring, the C ring. The saturated broad white band near the middle of the B ring is the densest region of the rings, over which two of the three radio signals were blocked at 10-kilometer (6-mile) resolution, preventing accurate color representation. From other evidence in the radio observations, all ring regions appear to be populated by a broad range particle size distribution that extends to boulder sizes (several to many meters across).

Radars
"This image [on the right] of Fort Irwin in California's Mojave Desert compares interferometric radar signatures topography -- data that were obtained by multiple imaging of the same region to produce three-dimensional elevation maps -- as it was obtained on October 7-8, 1994 by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar aboard the space shuttle Endeavour. Data were acquired using the L-band (24 centimeter wavelength) and C-band (6 centimeter wavelength). The image covers an area about 25 kilometers by 70 kilometers (15.5 miles by 43 miles). North is to the lower right of the image. The color contours shown are proportional to the topographic elevation. With a wavelength one-fourth that of the L-band, the results from the C-band cycle through the color contours four times faster for a given elevation change. Detailed comparisons of these multiple frequency data over different terrain types will provide insights in the future into wavelength-dependent effects of penetration and scattering on the topography measurement accuracy. Fort Irwin is an ideal site for such detailed digital elevation model comparisons because a number of high precision digital models of the area already exist from conventional measurements as well as from airborne interferometric SAR data."

"Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity."

"SIR-C was developed by NASA's Jet Propulsion Laboratory. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR), the major partner in science, operations and data processing of X-SAR."

Hydrogens
The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 [megahertz] MHz, which is equivalent to the vacuum wavelength of 21.10611405413 cm in free space. This wavelength or frequency falls within the microwave radio region of the electromagnetic spectrum, and it is observed frequently in radio astronomy, since those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light.

Venus
The first un-ambiguous detection of Venus was made by the Jet Propulsion Laboratory (JPL) on 10 March 1961. A correct measurement of the AU soon followed.

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."

When viewed using radio astronomy, the resulting radar image, at left, shows that just beneath the cloud layers is a rocky object.

Jupiter
In 1955, Bernard Burke and Kenneth Franklin detected bursts of radio signals coming from Jupiter at 22.2 MHz. The period of these bursts matched the rotation of the planet, and they were also able to use this information to refine the rotation rate. Radio bursts from Jupiter were found to come in two forms: long bursts (or L-bursts) lasting up to several seconds, and short bursts (or S-bursts) that had a duration of less than a hundredth of a second.

Forms of decametric radio signals from Jupiter:
 * bursts (with a wavelength of tens of meters) vary with the rotation of Jupiter, and are influenced by interaction of Io with Jupiter's magnetic field.
 * emission (with wavelengths measured in centimeters) was first observed by Frank Drake and Hein Hvatum in 1959. The origin of this signal was from a torus-shaped belt around Jupiter's equator. This signal is caused by cyclotron radiation from electrons that are accelerated in Jupiter's magnetic field.

Between September and November 23, 1963, Jupiter is detected by radar astronomy.

"The dense atmosphere makes a penetration to a hard surface (if indeed one exists at all) very unlikely. In fact, the JPL results imply a correlation of the echo with Jupiter ... which corresponds to the upper (visible) atmosphere. ... Further observations will be needed to clarify the current uncertainties surrounding radar observations of Jupiter."

"Although in 1963 some claimed to have detected echoes from Jupiter, these were quite weak and have not been verified by later experiments."

"A search for radar echoes from Jupiter at 430 MHz during the oppositions of 1964 and 1965 failed to yield positive results, despite a sensitivity several orders of magnitude better than employed by other groups in earlier (1963) attempts at higher frequencies. ... [I]t might be suspected that meteorological disturbances of a random nature were involved, and that the echoes might be returned only in exceptional circumstances. Further support for this point of view may be gleaned from the fact that JPL found positive results for only 1 (centered at 32° System I longitude) of the 8 longitude regions investigated in 1963 (Goldstein 1964) and, in fact, had no success during their observations in 1964 (see comment by Goldstein following Dyce 1965)."

"This VLA image of Jupiter [at right] doesn't look like a planetary disk at all. Most of the radio emission is synchrotron radiation from electrons in Jupiter's magnetic field."

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 [Gigahertz] GHz to as low as 3 [Kilohertz] kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers.

"Details in radiation belts close to Jupiter are mapped from measurements that NASA's Cassini spacecraft made of radio emission from high-energy electrons moving at nearly the speed of light within the belts."

"The three views show the belts at different points in Jupiter's 10-hour rotation. A picture of Jupiter is superimposed to show the size of the belts relative to the planet. Cassini's radar instrument, operating in a listen-only mode, measured the strength of microwave radio emissions at a frequency of 13.8 gigahertz (13.8 billion cycles per second or 2.2 centimeter wavelength). The results indicate the region near Jupiter is one of the harshest radiation environments in the solar system."

"From Earth-based radio telescopes, the telltale radio emissions would be swamped out by heat-generated radio emissions from Jupiter's atmosphere, but Cassini was close enough to Jupiter in January 2001 to differentiate between the emissions from the radiation belts and those from the atmosphere."

"The belts appear to wobble as the planet turns because they are controlled by Jupiter's magnetic field, which is tilted in relation to the planet's poles."

Saturn
"Three simultaneous radio signals at wavelengths of 0.94, 3.6, and 13 centimeters (Ka-, X-, and S-bands) were sent from Cassini through the rings to Earth. The observed change of each signal as Cassini moved behind the rings provided a profile of the distribution of ring material and an optical depth profile."

"This simulated image was constructed from the measured optical depth profiles of the Cassini Division and ring A. It depicts the observed structure at about 10 kilometers (6 miles) in resolution. The image shows the same ring A region depicted in a similar image (Multiple Eyes of Cassini), using a different color scheme to enhance the view of a remarkable array of over 40 wavy features called 'density waves' uncovered in the May 3 radio occultation throughout ring A."

"Color is used to represent information about ring particle sizes based on the measured effects of the three radio signals. Shades of red [purple] indicate regions where there is a lack of particles less than 5 centimeters (about 2 inches) in diameter. Green and blue shades indicate regions where there are particles of sizes smaller than 5 centimeters (2 inches) and 1 centimeter (less than one third of an inch), respectively."

"Note the gradual increase in shades of green towards the outer edge of ring A. It indicates gradual increase in the abundance of 5-centimeter (2-inch) and smaller particles. Note also the blue shades in the vicinity of the Keeler gap (the narrow dark band near the edge of ring A). They indicate increased abundance of even smaller particles of diameter less than a centimeter. Frequent collisions between large ring particles in this dynamically active region likely fragment the larger particles into more numerous smaller ones."

Boomerang nebula
The background purple structure (on the left), as seen in visible light with the NASA/ESA Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s ability to see the cold molecular gas reveals the nebula’s more elongated shape, in orange.

Since 2003 the nebula, located about 5000 light-years from Earth, has held the record for the coldest known object in the Universe. The nebula is thought to have formed from the envelope of a star in its later stages of life which engulfed a smaller, binary companion. It is possible that this is the cause of the ultra-cold outflows, which are illuminated by the light of the central, dying star.

ALMA looked at the nebula’s central dusty disc and the outflows further out, which span a distance of almost four light-years across the sky. These outflows are even colder than the cosmic microwave background, reaching temperatures below –270 °C. The outflows are also expanding at a speed of 590 000 kilometres per hour.

"The differential 850-μm counts are well described by the function


 * $$n(S) = N_0/(a + S^{3.2}),$$

where $$S$$ is the flux in mJy, $$N_0$$ = 3.0 × 104 per square degree per mJy, and $$a$$ = 0.4 − 1.0 is chosen to match the 850-μm extragalactic background light."

The "absorption and reradiation of light by dust in the history of galaxy formation and evolution is [...] the submillimeter extragalactic background light [(EBL). It] has approximately the same integrated energy density as the optical EBL."

Karl G. Jansky Very Large Array
Usually the Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory. The telescopes can operate over the wavelength range: 0.6 cm (50 GHz)–410 cm (73 MHz), or 6 mm (50 GHz)–4100 mm (73 MHz). The frequency coverage is 50 GHz to 74 MHz (7 mm to 4000 mm).

MeerKAT
Wavelength:	30 mm (10.0 GHz)–300 mm (1,000 MHz), or a centimeter to decameter telescope.

Suffa RT-70 radio telescope
The Suffa RT-70 radio telescope, 70 m dish and an operating range of 5–300 GHz (60 mm to 1 mm), is at the Suffa Radio Observatory on the Suffa plateau, Uzbekistan.

As of 2008, the Russian government had resumed the construction of the site, with an updated emphasis on millimeter-wave band observations at 100–300 GHz. As of 2014, construction was reported to be 50% complete.

With its 70m antenna diameter, this third unit of the RT-70 telescope was designed to be one of three similar radio telescopes.

Two completed RT-70 telescopes are:
 * Yevpatoria RT-70 radio telescope – at the Center for Deep Space Communications, Yevpatoria, Crimea
 * Galenki RT-70 radio telescope – at the Ussuriysk Astrophysical Observatory, Russia.

Yevpatoria RT-70 radio telescope
Yevpatoria RT-70 radio telescope has 70 m dish and an operating range of 5–300 GHz (60 mm to 1 mm).