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Topic: Aperture synthesis

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	Geoscience and Remote Sensing Society (Site not responding. Last check: 2007-09-16)
		Aperture synthesis is an interferometric technique in which the complex correlation of the output voltage from pairs of antennas is measured at different antenna spacings or baselines.
		Aperture synthesis was first applied in radio astronomy as a means to achieve high resolving power with an antenna array using a limited number of (relatively) small, individual elements.
		The objective of this research was to demonstrate the utility of aperture synthesis for remote sensing of the earth with specific application to the remote sensing of soil moisture and ocean salinity (two important observations made at L-band).
	www.ewh.ieee.org /soc/grss/ift/racett11.html (1483 words)

	ninemsn Encarta - Search Results - Aperture
		Aperture, in optics, the opening of a lens through which light can enter.
		In photography, the relative aperture, or f number, is the ratio of the...
		Aperture Synthesis, the combination of smaller radio telescopes to form, in effect, one very large telescope.
	au.encarta.msn.com /Aperture.html (86 words)

	* Aperture - (Astronomy): Definition
		The aperture and focal ratio of all telescopes are compromises determined by factors such as cost, weight, size as much as desired optical performance.
		The Venera 15 and 16 synthetic aperture radar (SAR) systems were identical, and were used to map the surface of Venus at a resolution of 1 to 2 kilometers (.6 to 1.2 miles) over a period of 8 months.
		22 divided by the aperture of the telescope.
	en.mimi.hu /astronomy/aperture.html (1223 words)

	Telescope - Wikipedia, the free encyclopedia
		Radio telescopes are often operated in pairs, or larger groups to synthesize large "virtual" apertures that are similar in size to the separation between the telescopes: see aperture synthesis.
		Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and Aperture Masking Interferometry at single telescopes.
		The four telescopes, belonging to ESO and located in the Atacama desert in Chile, are usually operated independently for faint astronomical observations, but up to three telescopes can be operated together for aperture synthesis observations of bright objects.
	en.wikipedia.org /wiki/Telescope (1981 words)

	Aperture synthesis -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-09-16)
		Aperture synthesis is a type of (Click link for more info and facts about interferometry) interferometry that mixes signals from a collection of instruments to produce measurements having the same (Click link for more info and facts about angular resolution) angular resolution as an instrument the size of the entire collection.
		At each separation and orientation, the lobe-pattern of the interferometer produces an output which is one component of the (Click link for more info and facts about Fourier transform) Fourier transform of the spatial distribution of the brightness of the observed object.
		Most aperture synthesis interferometers use the rotation of the Earth to increase the number of different baselines included in an observation (see diagram on right).
	www.absoluteastronomy.com /encyclopedia/a/ap/aperture_synthesis.htm (362 words)

	Qi, Chunhua (2000-08-21) Aperture synthesis studies of the chemical composition of protoplanetary disks and comets. ...
		Qi, Chunhua (2000-08-21) Aperture synthesis studies of the chemical composition of protoplanetary disks and comets.
		Aperture synthesis studies of the chemical composition of protoplanetary disks and comets
		The production rates derived from the aperture synthesis images are similar to those found by other researchers, and reveal a marked similarity between the composition of Hale-Bopp and that derived for dense molecular clouds, in particular the hot cores observed near massive young stars.
	etd.caltech.edu /etd/available/etd-11302001-000213 (590 words)

	Optical interferometry - Wikipedia, the free encyclopedia
		In the 1980s the aperture synthesis technique was extended to visible light and infrared astronomy by the Cavendish Astrophysics Group, providing the first very high resolution images of nearby stars.
		In 1995 this technique was demonstrated on an array of separate optical telescopes for the first time, allowing a further improvement in resolution, and allowing even higher resolution imaging of stellar surfaces.
		By moving the holes in the aperture mask and taking repeated measurements, images can be created using aperture synthesis which would have the same quality as would have been given by the right-hand telescope without the aperture mask.
	en.wikipedia.org /wiki/Optical_interferometry (977 words)

	Applications of the Canadian VLBI Correlator
		Such motion is usually provided by the rotation of the earth ("earth rotation synthesis") or in the case of Space VLBI by the motion of an orbiting antenna.
		The time it takes to adequately fill the aperture depends on the number of antennas and their spacing in the array, as well as the size and quality of the image.
		Techniques such as frequency switched bandwidth synthesis that synthesizes, at reduced cost, the effect of a wide RF band demand that everything from the RF electronics to the correlator be capable of handling the required signal processing.
	www.drao-ofr.hia-iha.nrc-cnrc.gc.ca /science/vlbi/oldweb/applications/applications.html (1088 words)

	NCSA RAI: HPDC
		An array of a large number of antennas all interconnected as interferometers measures simultaneously a large number of spatial frequency Fourier components; the radio image (with an angular resolution determined by the separation of the individual antennas) is then formed in a digital computer by Fourier transformation of the observed visibilities.
		Because the images produced by a synthesis array are formed in a digital computer by Fourier transformation of the observed visibilities, the computer system is an integral part of the synthesis array telescope - its image-forming element.
		Sparse sampling of the aperture plane results in strong sidelobes (i.e., large spurious responses away from the principal maximum); this instrumental signature may be removed by computationally intensive non-linear deconvolution techniques.
	monet.ncsa.uiuc.edu /hpcc/HPDC.html (493 words)

	Image Retrieval Theory of Synthetic Aperture Radiometer for Microwave Remote Sensing
		Since for low earth orbit or airborne platforms the aperture synthesis can be separated as cross track and along track, the method then can be developed separately too.
		In fact, the aperture synthesis theory in cross track direction has already been development by Le Vine and Swift, et al [1][2], which is rather similar to the aperture synthesis technique in radio astronomy.
		Since the along track aperture synthesis can thin the aperture very much, it will use mush less element and correlate's than the conventional two dimensional aperture synthesis technique, for example the Y shape or U shape synthetic aperture radiometers.
	www.gisdevelopment.net /aars/acrs/1999/ps6/ps61196pf.htm (2274 words)

	[No title]
		The Aperture Synthesis set of applications could be be considered the heart of AIPS++, because it deals with the UV-data that are generated by the various Consortium interferometers.
		The firmness of the Aperture Synthesis design owes much to the practical work in the Single Dish stream, which is a few months ahead of Aperture Synthesis.
		However, the Aperture Synthesis designers are aware of the A-matrix concept, and the present design does not preclude it in any way.
	aips2.aoc.nrao.edu /docs/notes/177.text (1492 words)

	MakeRF
		At any time it is possible to inspect different antenna characteristics like the shape of main or sub-reflectors, the field on the antenna aperture, etc. and observe what is happening with the antenna system during the synthesis.
		A conic system has a circular aperture, the aperture power distribution is almost identical to the feed taper.
		Reflector GO synthesis reshapes the conic system (which is used as a starting point) to a system with an elliptical aperture and given aperture taper.
	www.maasdesign.co.uk /maker.html (619 words)

	[No title] (Site not responding. Last check: 2007-09-16)
		Aperture synthesis maps of vibrationally excited Cyanoacetylene in Orion-KL, Plambeck, R.L. \& Wright, M.C.H., 1986, BAAS, 18, 2 Sub-arcsecond 2-cm continuum and SiO spectral line observations of R Aquarii, Hollis, J. M., Michalitsianos, A. G., Kafatos, M., Wright, M. H., \& Welch, W. J., 1986, ApJ 309, L47.
		86 GHz aperture synthesis observations of the Galactic center, Wright, M.C.H., Genzel, R., Guesten, R. \& Jaffe, D.T. 1987, Proceedings of the Symposium on the Galactic Center in Honor of Charles H. Townes, AIP Conf.
		Hat Creek aperture synthesis observations of the circum-nuclear ring in the Galactic center, Guesten, R., Genzel, R., Wright, M.C.H., Jaffe, D.T., Stutzki, J., \& Harris, A., 1987, Proceedings of the Symposium on the Galactic Center in Honor of Charles H. Townes, AIP Conf.
	astron.berkeley.edu /~wright/publications.txt (1855 words)

	Bibliographie des DLR (LIDO) (Site not responding. Last check: 2007-09-16)
		For this situation the imaging principle of aperture synthesis from radio astronomy has to be applied.
		The advanced method of aperture synthesis as a new approach for high resolution passive imaging is comprehensively discussed and simulated system design examples are illustrated.
		The imaging performance of aperture synthesis is investigated using measured high resolution W-band data of typical military targets as an ideal input brightness temperature distribution.
	www.dlr.de /lido/HR/2004/2013632004.html (365 words)

	Seminar abstract Jaap Bregman (Site not responding. Last check: 2007-09-16)
		Known realizations of aperture synthesis radio telescopes cannot be scaled to fit the challenging one kilometer squared collecting area within a budget of 200 M$.
		To cover the 0.2 - 1.8 GHz frequency range of interest with half wave receptor sampling of the aperture in both polarizations, leads to the afore mentioned specification for the 30 telescopes that form the synthesis array.
		A hierarchical approach subdivides the total aperture typically into 10,000 tiles each with 1000 active receptors and RF processing to produce 100 output beams.
	www.atnf.csiro.au /SKA/jbregman_961126.html (319 words)

	Telescopes.Rifle-Scope-Alley.Com :- (Site not responding. Last check: 2007-09-16)
		Aperture synthesis is now also being applied to optical telescopes.
		A new era of telescope making was inaugurated by the MMT, a synthetic aperture composed of six segments synthesizing a mirror of 4.5 metres diameter.
		It is now part of a synthetic aperture array with several other Mt. Wilson telescopes, and is still useful for advanced research.
	telescopes.rifle-scope-alley.com (1233 words)

	Search Results for aperture - Encyclopædia Britannica
		The size of an aperture is limited by the size of the mount holding the optical component, or the size of the...
		The aperture, or f-number, is the ratio of the focal length to the diameter of an incident light beam as it reaches the lens.
		The correct exposure (aperture and shutter settings) can be derived from tables or calculators or by direct measurement of the subject luminance with a light meter.
	www.britannica.com /search?query=aperture&submit=Find&source=MWTEXT (512 words)

	MSN Encarta - Search Results - Aperture
		White's photographs were displayed in dozens of individual and group exhibitions, and were published widely.
		Aperture Synthesis, in radio astronomy, the combination of smaller radio telescopes to form, in effect, one very large telescope.
		Exclusively for MSN Encarta Premium Subscribers--quickly search thousands of articles from magazines such as Time, Newsweek, The Atlantic Monthly, and Smithsonian.
	ca.encarta.msn.com /Aperture.html (89 words)

	3.1 Introduction
		This Chapter is for potential MERLIN users who are not familiar with aperture synthesis observations and its jargon.
		§3.3-3.7 give a qualitative overview of the features of aperture synthesis which are relevant for planning observations.
		They are not intended to explain in detail how aperture synthesis works, although you will certainly need to have a good idea about this to get the best from your data if the target is very bright or extended.
	www.merlin.ac.uk /user_guide/OnlineMUG/newch0-node31.html (830 words)

	Ultrasonic Synthetic Aperture Holographic Imaging by RICHARD Y (Site not responding. Last check: 2007-09-16)
		The lateral resolution of such images is limited by the aperture size of the transducer, while the depth resolution is limited by the pulse width.
		In addition, for a given aperture diameter, the lateral resolution degrades with depth as given by the Rayleigh and other criteria.
		The synthetic aperture method allows efficient volume inspection by trading off scan time with processing time, the latter of which is constantly improving with increasing computing power.
	www.cnde.iastate.edu /QNDEDatabase/Vol.11A/p0813-0820.html (354 words)

	The Time Interferometer: Synthesis of the Correlation Function
		The aperture synthesis technique well known in radio astronomy is adapted to the spectral analysis of the time series.
		When an interferometer is used, the aperture is not solid, and what we can measure is the visibility data, i.e., the estimator of the spectrum of spatial frequencies.
		It is known that to do aperture synthesis one must have an interferometer with the changeable baseline.
	www.adass.org /adass/proceedings/adass96/vityazevv2.html (1273 words)

	PSIgate - Physical Sciences Information Gateway: Search/Browse Results (Site not responding. Last check: 2007-09-16)
		This interactive tutorial 'explores the effects of objective numerical aperture on the resolution of the central bright disks present in the diffraction pattern, commonly known as Airy disks'.
		Research interests include: optical aperture synthesis; cosmic microwave background; submillimetre-wave instrumentation; star formation; exotic galaxies and active galactic nuclei; low-frequency surveys and variability; origin of galaxies and galaxy formation; geometric algebra; and inferential science.
		HERA-B is a large aperture high rate spectrometer built for studies of collisions of protons with the nuclei of target wires positioned in the halo of the HERA proton beam.
	www.psigate.ac.uk /roads/cgi-bin/psisearch.pl?term1=aperture&limit=0&subject=All (1727 words)

	Masked pupil speckle imaging and aperture synthesis (Site not responding. Last check: 2007-09-16)
		Pupil masks allow to select a sub-sample of spatial frequencies and more accurately measure the corresponding complex visibilities since they will be less attenuated (as the overlap of the fringes is lower); hence, a better use of the maximum number of photons set by the detector.
		The price to pay is to perform an interpolation in the Fourier space (aperture synthesis, see methods in §5.1) and complementary observations to make the process more robust.
		A successful image of HR8652 was restored using these masks and the aperture synthesis method from Lannes (1989, 1991) and Anterrieu (1992) (Cf.
	webast.ast.obs-mip.fr /people/prieur/pisco/node7.html (235 words)

	Optical Aperture Synthesis Homepage (Site not responding. Last check: 2007-09-16)
		We continue to exploit aperture synthesis and other methods at a number of the world's largest optical and infrared telescope to realise diffraction limited images without recourse to adaptive optics.
		Studies such as these are being used to explore, for example, surface activity on supergiants, the structure and origin of the dust envelopes of AGB stars and planetary nebula progenitors, and the populations of crowded stellar clusters.
		This telescope, the Cambridge Optical Aperture Synthesis Telescope (COAST), was developed in the 1990's as the world's first optical synthesis array.
	www.mrao.cam.ac.uk /research/OAS.html (326 words)

	CERFACS: Signal & Image Processing Team (Site not responding. Last check: 2007-09-16)
		ABSTRACT- The idea of aperture synthesis is to obtain a high angular-resolution image by using interferometric information corresponding to spatial frequencies distributed over a wide virtual pupil.
		The inverse problems of image reconstruction in aperture synthesis are very particular myopic deconvolution problems, because the constraints on the transfert function can easly be imposed.
		We first present a new formularion of these algebraic structures and their algorithmic implications in aperture synthesis.
	www.cerfacs.fr /dsp/papers/phd1.html (148 words)

	8 (Site not responding. Last check: 2007-09-16)
		Later, the radiating aperture of the experimental prototype RLSA antennas have been fabricated by the printed-circuit technology and those antennas have been tested in the compact antenna measurement assembly (Fig.
		It is apparent thanks acceptable level of antenna performances achieved that developed theoretical models and their implementation in the synthesis procedure give available design accuracy under condition of exactly known dielectric constant of used materials.
		Experimental amplitude distribution of aperture field of the 200 mm diameter RLSA antenna for some set of aperture efficiency (AE) implemented for definite operation frequency of antenna with features in Fig.
	www.ecs.umass.edu /ece/allerton/papers1999/27 (3788 words)

	Principles of aperture synthesis (Site not responding. Last check: 2007-09-16)
		The uv-plane is parallel to the tangent plane at the phase centre on the celestial sphere and rotates with the rotation of the Earth.
		An aperture synthesis telescope, like the GMRT, consists of a number of antennas located on the ground and the resolution of such a telescope is proportional to the maximum projected separation between the antennas.
		Due to the rotation of the earth, the projected separations between the antennas change as the antennas track a source in the sky.
	www.ncra.tifr.res.in /~sanjay/thesis/node25.html (1628 words)

	C. Swift Research (Site not responding. Last check: 2007-09-16)
		Unlike Synthetic Aperture Radar, where time-Doppler processing can be used to achieve the fine resolution comparable to that achieved with optical systems, microwave radiometers require large antennas as the only means to improve spatial resolution.
		Because of the potential expense associated with placing large, filled apertures into space, the concept of aperture synthesis was explored in the 1980's as a means to address this problem.
		This instrument demonstrated the success of aperture synthesis and provided scientific results for soil moisture.
	www.ecs.umass.edu /ece/labs/antlab/Swift_research_page.html (237 words)

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