P. C. Crane

SpecTIR™ Remote Sensing Division, Reno, Nevada, United States

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Publications (48)55.67 Total impact

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    ABSTRACT: We report ultraviolet optical observations from space of a Medium-Scale Traveling Ionospheric Disturbance (MSTID) made during the Combined Radio Interferometry and COSMIC Experiment in Tomography Campaign (CRICKET) held on September 15, 2007 at ∼8:30 UT. The experiment used a Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC also known as FORMOSAT-3) satellite in conjunction with the Very Large Array (VLA) radio telescope, located near Socorro, NM, to study the ionosphere from the global scale down to the regional scale while the TIDs propagated through it. The COSMIC/FORMOSAT-3 satellite measured the F region electron density both horizontally and with altitude while the VLA measured the directions and speeds of the TIDs. These observations provide new information on this poorly understood class of TID and demonstrate the possibility of studying MSTIDs using space-based optical instruments.
    Radio Science 01/2011; 46(5). · 1.00 Impact Factor
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    ABSTRACT: The Long Wavelength Array (LWA) is part of a new class of large low-frequency interferometric telescopes. The complete LWA will consist of more than 50 phased array "stations" distributed over a roughly 400 km diameter region in New Mexico. Each station will consist of 256 pairs of dipole-type antennas whose signals are formed into beams, with outputs transported to a central location for high-resolution aperture synthesis imaging. The resulting image sensitivity is estimated to be a few mJy with a resolution of 8" to 2" (20 to 80 MHz). Phase I of the LWA is nearly complete, with completion of PDR, construction of the first full station (LWA-1) in 2009-10, and operation as a stand-alone instrument in 2010. Utilizing modern FPGA computing, LWA-1 will form four independent (in both frequency and pointing) beams on the sky, and provide instantaneous bandwidths of 8 MHz per beam, spectral resolutions down to 100 Hz, and temporal resolutions down to 0.1 ms in the range of 10 to 88 MHz. Signals from 512 dipole antennas will be digitized without frequency conversion (a homodyne receiver architecture), allowing direct beam-formation of the entire LWA bandwidth. As the station will operate as a fully electronic phased array, very little repointing time is required. This will allow the beams to be cycled rapidly among many calibration sources on millisecond timescales. This scheme could provide real-time calibration of the turbulent ionospheric conditions, which limit both resolution and sensitivity at low-frequencies. The LWA Project is funded through a contract from the Office of Naval Research to the University of New Mexico. Partnering with UNM are the Naval Research Laboratory, Virginia Tech, the Jet Propulsion Laboratory, Los Alamos National Laboratory, and the University of Iowa. Basic research in radio astronomy at the Naval Research Laboratory is supported by 6.1 base funding.
    05/2009;
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    ABSTRACT: Several decades ago, instruments like the Very Large Array (VLA) first opened the GHz frequency sky to high dynamic range imaging. Today, a path-finding VLA 74 MHz system is providing the first sub-arcminute resolution view of the radio universe below 100 MHz, a technical innovation inspiring an emerging suite of large (> 100 km), much more powerful long-wavelength instruments including the Long Wavelength Array (LWA). Similar in philosophy to the VLA and also located in New Mexico, the LWA will be a versatile, user-oriented electronic array designed to open the 20--80 MHz frequency range to detailed exploration for the first time. The LWA's mJy sensitivity and near-arcsecond resolution will surpass, by 2--3 orders of magnitude, the imaging power of previous interferometers in its frequency range. LWA scientific frontiers include: (1) the high-z universe, including distant radio galaxies and clusters - tools for understanding the earliest black holes and the cosmological evolution of Dark Matter and Dark Energy, respectively; (2) acceleration, propagation, and turbulence in the ISM, including the space-distribution and spectrum of Galactic cosmic rays and supernova remnants; (3) planetary, solar, and space science, including space-weather prediction and extra-solar planet searches; and (4) the radio transient universe including GRBs, ultra-high energy cosmic rays, and new sources of unknown origin. Because the LWA will explore one of the most poorly investigated spectral regions the potential for new discoveries is high, and there is a strong synergy with exciting new X-ray and Gamma-ray measurements. The LWA will also provide an unparalleled measure of small-scale ionospheric structure, a pre-requisite for accurate calibration and imaging. This presentation focuses on LWA science, while a companion paper reviews the technical design subjected to Preliminary Design Review in March 2009. Basic research in radio astronomy at the Naval Research Laboratory is supported by 6.1 base funding.
    05/2009;
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    ABSTRACT: We report on the Combined Radio Interferometry and COSMIC Experiment in Tomography Campaign (CRICKET) held on September 15 and 17, 2007. The experiment used the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC also known as FORMOSAT-3) in conjunction with the Very Large Array radio telescope, located near Socorro, NM, to study the ionosphere from the global scale down to the regional scale. Each COSMIC satellite includes three instruments capable of measuring the ionosphere: the Tiny Ionospheric Photometer (TIP), a UV radiometer; the GPS Occultation experiment (GOX), a dual-frequency GPS occultation receiver; and the Tri-band Beacon (TBB), a three frequency coherently radiating radio beacon. These three instruments have been demonstrated to be a powerful means for characterizing the global-scale ionosphere. The VLA when deployed at its largest extent and while operating at 73.8 MHz is incredibly sensitive to relative total electron content variations of the regional ionosphere over about a 30-100 km diameter area. In this work, we concentrate on the first set of observations on September 15, 2007 at approximately 0830 UT. We have successfully married these heterogeneous data sets, using a tomographic data fusion approach, to produce a consistent ionospheric specification from the global scale down to the regional scale.
    01/2008; 37:775.
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    ABSTRACT: The LWA, the Long Wavelength Array, is a phased aperture array radio telescope that is being built in New Mexico. When completed the array will comprise 52 stations, each with 256 dipoles, spread across the state of New Mexico with baseline lengths up to 400 km. The LWA is optimized for the frequency range 20-80 MHz, thus corresponding to angular resolutions of about 2 arcseconds at the higher frequencies. Currently several locations are being evaluated as possible LWA station sites. The site selection is partly determined by the imaging capability of the final array, but is also affected by factors like availability of land, power, access to optical fiber, and the radio frequency intereference (RFI) environment. Here we describe the ongoing effort of characterizing the RFI environment at candidate LWA station sites. The LWA project is led by the University of New Mexico and include as partners the Naval Research Laboratory, the Los Alamos National Laboratory, the Applied Research Laboratory of the University of Texas, the University of Iowa, and Virginia Tech.
    12/2007;
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    ABSTRACT: The NRL Long-Wavelength Test Array (NLTA) was constructed to develop and test active baluns and electrically short dipoles for possible use as the primary wideband receiving elements for an emerging suite of large HF/VHF arrays including the Low Frequency Array (LOFAR) and the Long-Wavelength Array (LWA). Several dipoles of various designs and dimensions have been built and tested. Their useful range is when the dipoles arms are between approximately 1/8 and one wavelength long and the feedpoint is less that one half wavelength above ground. The NLTA, operating as an interferometer, has observed fringes from the brightest celestial sources in the frequency range from 10 to 50 MHz. The antenna temperatures vary from about 10% to 100% of the average brightness temperature of the Galactic background. With these parameters, it is relatively easy to make the amplifier noise levels low enough so that final system temperature is dominated by the Galactic background.
    06/2007;
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    ABSTRACT: Transient radio sources are necessarily compact and usually are the locations of explosive or dynamic events, therefore offering unique opportunities for probing fundamental physics and astrophysics. In addition, short-duration transients are powerful probes of intervening media owing to dispersion, scattering, and Faraday rotation that modify the signals. While radio astronomy has an impressive record obtaining high time resolution, usually it is achieved in quite narrow fields of view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X-ray and gamma-ray bands. Operating in the 20-80 MHz range, the Long Wavelength Array (LWA) is one of a suite of next-generation radio telescopes that will explore the radio transient sky. Composed of phased "stations" of dipoles, the LWA can probe the sky for transients on a range of angular and temporal scales, by using an individual station to scan much of the sky or correlating the signals from multiple stations to monitor possible transients. Numerous classes of radio transients, both known and hypothesized, are accessible to the LWA, ranging from cosmic ray air showers and Jovian emission, to bursts from extrasolar planets or other coherent emitters and prompt emission from gamma-ray bursts, to possible electromagnetic counterparts of gravitational wave burst sources. We summarize the scientific potential of radio transient observations with the LWA as well as some of the technical challenges, the most notable of which is the robust excision or avoidance of radio frequency interference (RFI). Basic research in radio astronomy at the NRL is supported by the Office of Naval Research.
    08/2006;
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    ABSTRACT: As part of a program to study particle acceleration in radio galaxies, we have observed Cygnus A at 74 and 327 MHz with the Very Large Array's Pietown link, obtaining angular resolutions of approximately 10" and 3", respectively. These observations are among the highest angular resolutions obtained below 1000 MHz for this object and serve as prototypes for observations with the Long Wavelength Array. Guided by a 151 MHz image from MERLIN and the 327 MHz image, we have estimated the 74 MHz emission from the hot spots. We confirm that the emission from both the western and eastern hot spots flattens at low frequencies and that there is a spectral asymmetry between the two. For the eastern hot spot, a low-energy cutoff in the electron energy spectrum appears to explain the flattening, which implies a cutoff Lorentz factor gamma' 300, though we cannot exclude the possibility that there might be a moderate level of free-free absorption. For the western hot spot, the current observations are not sufficient to distinguish between a free-free absorped power-law spectrum and a synchrotron self-absorbed spectrum. We also anticipate obtaining similar observations of 3C 219, and a preliminary analysis of these will be presented as well.The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Basic research in radio astronomy at the NRL is supported by the Office of Naval Research.
    06/2006;
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    ABSTRACT: Nearly three decades ago, the Very Large Array (VLA) first opened the 1-20 GHz radio sky to detailed study. Today, a path-finding VLA 74 MHz system is providing the first sub-arcminute resolution view of the radio universe below 100 MHz, a technical innovation that has inspired an emerging suite of much more powerful low-frequency instruments. Similar in philosophy to the VLA and also located in New Mexico, the Long Wavelength Array (LWA) will be a versatile, user-oriented electronic array poised to open the 20--80 MHz frequency range to detailed exploration for the first time. With a collecting area of one million square meters, the LWA will be a square kilometer telescope whose milli-Jansky sensitivity and near-arcsecond resolution will surpass, by 2--3 orders of magnitude, the imaging power of previous interferometers in its frequency range. LWA scientific frontiers include (1) the high-z universe, including distant radio galaxies and clusters - tools for understanding the earliest black holes and the cosmological evolution of Dark Matter and Dark Energy, respectively; (2) acceleration, propagation, and turbulence in the ISM, including the space-distribution and spectrum of Galactic cosmic rays and supernova remnants; (3) planetary, solar, and space science, including space-weather prediction and extra-solar planet searches; and (4) the radio transient universe including GRBs, ultra-high energy cosmic rays, and new sources of unknown origin. Because the LWA will explore one of the most poorly investigated spectral regions the potential for new discoveries is high, and there is a strong synergy with exciting new X-ray and Gamma-ray measurements, e.g. for cosmic ray acceleration, transients, and galaxy clusters. The LWA will also provide an unparalleled measure of small-scale ionospheric turbulence, a pre-requisite for accurate calibration and imaging. Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research.
    AGU Spring Meeting Abstracts. 04/2006; -1:04.
  • 01/2006;
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    ABSTRACT: We document here the development of the site for the LWDA. It is located just inside the southwest corner of the central section of the Very Large Array (VLA). This site has been chosen because of the availability of land, easy access to power, only a short optical fiber connection to the VLA correlator and 74 MHz signals from the VLA antennas, and because VLA resources could be available to assist in the site preparation. The site is sandy and firm but well drained with a low, thin vegetative cover. Consequently, the site did not require significant earthmoving, stripping of vegetation, nor application of gravel to stabilize the soil. These factors greatly reduce the cost of development. A fence surrounds the site to discourage the local fauna and a road is in place between the site and the Antenna Assembly Building of the VLA. An optical fiber connection runs to the VLA network at station CW7. A 1000-foot buried cable brings power from a nearby high-voltage power line of the local electric cooperative. A 6 x 2.4 x 2.5 meter windowless metal container is being used as the shielded room for the electronic equipment. Sixteen blade-style crossed-dipole antennas have been installed in the northwestern section of the site area. They represent one "pod" of a future LWA station of probably 256 dipoles. Baluns and receivers will be installed for each antenna and the signals will be brought to a 16-antenna hub for further processing and transmission to the correlator.
    01/2006;
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    ABSTRACT: We present new designs for active antenna systems optimized for HF/VHF radio astronomy, ionospheric science, space weather, and other radio science applications. Active antenna designs have been developed and tested which satisfy the need for high linearity and stability while achieving Galactic background dominated noise levels. The presence of very strong terrestrial radio-frequency interference (RFI), and world-wide propagation at these frequencies require that the preamplifiers have very high dynamic range. Distortion products must be below the Galactic background level for RFI mitigation techniques to be successful. Individual antennas should have broad response patterns to cover most of the sky without pointing mechanisms, but with decreased sensitivity at low elevations. Ideal designs would also be immune to environmental effects such as temperature variations and precipitation. For projects such as the LWA, where thousands of receptors will be needed, they must also be robust, inexpensive, and easy to manufacture and install. We discuss high-performance designs that are optimized for cost-sensitive applications such as the LWA. Basic research in astronomy is supported by the Office of Naval Research.
    12/2005;
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    ABSTRACT: We document the selection of the site for the Long Wavelength Demonstration Array (LWDA). The site is located just inside the southwest corner of the central section of the Very Large Array. The VLA site has been chosen because of the availability of land, for easy access to power and an optical fiber connection to the VLA correlator and to 74-MHz signals from VLA antennas, and because VLA resources might be available to assist in the site preparation. The site chosen is flat but slopes downward 2 degrees to the north. The soil is sandy and firm but well drained with a low, thin vegetative cover. The site, consequently, will not require significant earthmoving, stripping of vegetation, nor a layer of gravel to stabilize the soil. These factors will greatly reduce the cost of developing the site compared to the previous choice. A road will connect the site to a gate near the Antenna Assembly Building; and optical fiber, to the VLA optical-fiber network at station CW7. The local electric cooperative will bury 1600 feet of power cable from their nearby high-voltage power line to the site. The site will be fenced in and an electronics hut installed. Then the locations for the individual dipoles will be surveyed, the mounts and masts erected, and the power and digital cables installed. Finally, the receivers and blades will be installed. Soil tests indicate that the mounts will be easily driven to the desired depth to hold the antennas firmly in place. Experience with a test antenna showed the necessity for an anti-antelope fence and other measures to protect the equipment from the local fauna. Radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research.
    AGU Spring Meeting Abstracts. 12/2005;
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    ABSTRACT: The Long Wavelength Array (LWA) is a next-generation low-frequency telescope being built in New Mexico by the Southwest Consortium (UNM, UT-ARL, NRL, LANL). The LWA will operate at any frequency between 20 to 80 MHz. It will consist of 52 phased array-dipole stations, each acting in an equivalent way to an antenna in an interferometric array. Here, we describe a proposed array configuration and discuss its properties. Among the many considerations are: (1) adequate snapshot UV-coverage for calibration (2) sensitivity to large scale diffuse structure (3) achieving high resolution with up to 400 km baselines and (4) high imaging fidelity. Unlike the VLA, the LWA stations are not movable, so each of these goals must be achieved simultaneously with a single array configuration. The LWA is being constructed in phases, and we discuss the capabilities and considerations of each phase. Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research.
    12/2005;
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    ABSTRACT: Transient radio sources are necessarily compact and usually are the locations of explosive or dynamic events, therefore offering unique opportunities for probing fundamental physics and astrophysics. In addition, short-duration transients are powerful probes of intervening media owing to dispersion, scattering, and Faraday rotation that modify the signals. While radio astronomy has an impressive record obtaining high time resolution, usually it is achieved in quite narrow fields of view. Consequently, the dynamic radio sky is poorly sampled, in contrast to the situation in the X-ray and gamma -ray bands. Operating in the 20--80 MHz range, the Long Wavelength Array (LWA) is one of a suite of next-generation radio telescopes that will explore the radio transient sky. Composed of phased ``stations'' of dipoles, the LWA can probe the sky for transients on a range of angular and temporal scales, by using an individual station to scan much of the sky or correlating the signals from multiple stations to monitor possible transients. Numerous classes of radio transients, both known and hypothesized, are accessible to the LWA, ranging from cosmic ray air showers and Jovian emission, to bursts from extrasolar planets or other coherent emitters and prompt emission from gamma -ray bursts, to possible electromagnetic counterparts of gravitational wave burst sources. We summarize the scientific potential of radio transient observations with the LWA as well as some of the technical challenges, the most notable of which is the robust excision or avoidance of radio frequency interference (RFI). Basic research in radio astronomy at the NRL is supported by the Office of Naval Research.
    12/2005;
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    ABSTRACT: Application of self-calibration techniques to low-frequency (< 150 MHz) radio interferometric data has enabled high-resolution, high sensitivity imaging at long wavelengths for the first time. We illustrate these advances using NRAO Very Large Array (VLA) 74 MHz images having sub-arcminute resolution and sub-Jansky sensitivity. The VLA 74 MHz breakthrough has inspired the Long Wavelength Array (LWA), a completely electronic array planned to operate in the 20-80 MHz frequency range. It will have close to a square kilometer of collecting area at 20 MHz, milliJansky sensitivity, and arcsecond resolution. The LWA will surpass, by 2-3 orders of magnitude, the power of previous interferometers in its frequency range, and thus open a new window on the electromagnetic spectrum. Key LWA scientific drivers include cosmic evolution, cosmic ray acceleration, and space weather. The LWA will also be versatile instrument for studying radio transient phenomena, which may also include Jupiter-like emission from extra-solar planets. Because the LWA efficiently explores one of the last remaining areas of astrophysical discovery space, new classes of sources and physical phenomena are expected.
    11/2005; 345:392.
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    ABSTRACT: An initial survey of the radio-frequency environment at the site of the Long Wavelength Demonstration Array (LWDA) has been performed using a measurement protocol developed for both the Long Wavelength Array (LWA) and the Frequency Agile Solar Radiotelescope (FASR). The measurements cover the frequency range from 25 MHz to 18 GHz to include the LWA (23-80 MHz) and FASR (30 MHz-30 GHz). Measurements were obtained nearly continuously for a week to characterize the day/night and weekday/weekend variations expected for many sources of RFI. The equipment, antennas, and protocols are suitable for measuring strong RFI that potentially threatens the linearity of radio-astronomical receivers and may therefore rule out possible sites or influence the design of the receivers. (Weak RFI which may obscure weak signals of interest is beyond the capabilities of these measurements.) The protocol seeks only to identify RFI originating from terrestrial sources; RFI from satellites and astrophysical sources is assumed to be site independent and not a factor in site selection. Therefore, the receiving antennas provide azimuthal coverage in the direction of the horizon. This first survey, conducted prior to the start of LWDA construction, establishes a baseline for the later identification of any self-generated interference from the LWDA and its mitigation to ensure no adverse effect on the operations of the VLA.
    11/2005; 37:1389.
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    ABSTRACT: We are developing and testing active baluns and electrically short dipoles for possible use as the primary wideband receiving elements in the Long Wavelength Array (LWA) for HF-VHF radio astronomy. Several dipoles of various designs and dimensions have been built and tested. Their useful range occurs when the dipole arms are approximately 1/8 to one wavelength long and the feedpoint is less than 1/2 wavelength above ground. An eight-element NRL LWA Test Array (NLTA) interferometer has been built and fringes have been observed from the brightest celestial sources in the frequency range from 10 MHz to 50 MHz. The antenna temperatures vary from about 10% to 100% of the average brightness temperature of the galactic background. With these parameters it is easy to make the amplifier noise levels low enough that final system temperature is dominated by the galactic background.
    11/2005; 345:433.
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    ABSTRACT: We present spectra of solar bursts observed with active antenna prototypes. Combining active antenna systems developed for the NLTA (NRL Long-wavelength Test Array) and experience gained from BIRS (Bruny Island Radio Spectrometer) we have developed the GDRT (Goddard Decametric Radio Telescope). The GDRT and Green Bank Solar Radio Burst Spectrometer (GB/SRBS) serve as the northern hemisphere companions to BIRS, which operates in Tasmania. These instruments continuously scan from <12 MHz to >100 MHz while simultaneously applying RFI mitigation algorithms to produce a continuous record of solar activity. This space weather initiative demonstrates one application of hardware developed for the LWA (Long Wavelength Array).
    11/2005; 345:181.
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    ABSTRACT: We present an overview of the low-frequency array (LOFAR) that will open a window on one of the last and most poorly explored regions of the electromagnetic spectrum. LOFAR will be a large (baselines up to 400 km), low-frequency aperture synthesis array with large collecting area ( at ) and high resolution (∼1.5″ at 100 MHz), and will provide sub-mJy sensitivity across much of its operating range. LOFAR will be a powerful instrument for solar system and planetary science applications as reviewed by papers in this monogram. Key astrophysical science drivers include acceleration, turbulence, and propagation in the galactic interstellar medium, exploring the high red-shift universe and transient phenomena, as well as searching for the red-shifted signature of neutral hydrogen from the cosmologically important epoch of re-ionization.
    Planetary and Space Science 12/2004; · 2.11 Impact Factor

Publication Stats

193 Citations
55.67 Total Impact Points

Institutions

  • 2011
    • SpecTIR™ Remote Sensing Division
      Reno, Nevada, United States
  • 2006
    • University of New Mexico
      Albuquerque, New Mexico, United States
  • 1983
    • Pennsylvania State University
      University Park, Maryland, United States
  • 1980
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States
  • 1975
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States