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  • 1
    In: Radio Science, December 2012, Vol.47(6), pp.n/a-n/a
    Description: A new method of absolute calibration of sky noise temperature using a three‐position switched spectrometer, measurements of antenna and low noise amplifier impedance with a vector network analyzer, and ancillary measurements of the amplifier noise waves is described and compared with other methods of calibration. An initial test of the method has been made using brief observations from 55 to 110 MHz at West Forks, Maine, to estimate the sky noise spectral index. Estimates are made of the accuracy that might ultimately be achieved with observations to detect or set limits on the red‐shifted 21 cm line at a radio quiet site. It is concluded that an antenna reflection coefficient better than about −20 dB is required to avoid being limited by the accuracy of the antenna reflection coefficient measurements using a vector network analyzer. Absolute calibration of antenna and spectrometer for sky noise measurements
    Keywords: Antenna ; Calibration ; Spectrometer
    ISSN: 0048-6604
    E-ISSN: 1944-799X
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  • 2
    Description: New massively redundant low frequency arrays allow for a novel investigation of closure relations in interferometry. We employ commissioning data from the Hydrogen Epoch of Reionization Array to investigate closure quantities in this densely packed grid array of 14m antennas operating at 100 MHz to 200 MHz. We investigate techniques that utilize closure phase spectra for redundant triads to estimate departures from redundancy for redundant baseline visibilities. We find a median absolute deviation from redundancy in closure phase across the observed frequency range of about 4.5deg. This value translates into a non-redundancy per visibility phase of about 2.6deg, using prototype electronics. The median absolute deviations from redundancy decrease with longer baselines. We show that closure phase spectra can be used to identify ill-behaved antennas in the array, independent of calibration. We investigate the temporal behavior of closure spectra. The Allan variance increases after a one minute stride time, due to passage of the sky through the primary beam of the transit telescope. However, the closure spectra repeat to well within the noise per measurement at corresponding local sidereal times (LST) from day to day. In future papers in this series we will develop the technique of using closure phase spectra in the search for the HI 21cm signal from cosmic reionization. Comment: 32 pages. 11 figures. Accepted to Radio Science
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics
    ISSN: 00486604
    E-ISSN: 1944799X
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  • 3
    Language: English
    In: Eos, Transactions American Geophysical Union, 04/06/1999, Vol.80(14), pp.153-159
    Description: Robotic balloons, also known as aerobots, have become candidates for collecting atmospheric data and detailed surface observations of Venus, Mars, and Titan. A mission to Venus over a decade ago used two of them. Their inclusion last year in attempts by a balloonist to circumnavigate the Earth aptly demonstrated their utility for remote sensing and in situ observations of planetary atmospheres. To simulate aspects of an aerobot mission, a small payload to measure local atmospheric conditions and balloon position and velocity was included on Solo Spirit “Round the World” flights during January and August of last year. These missions, flown in Roziere balloons, were attempts by Steve Fossett to become the first person to circumnavigate the globe in a balloon without stopping. Neither attempt was successful, but the aerobot came through with flying colors.
    ISSN: Eos, Transactions American Geophysical Union
    E-ISSN: 00963941
    E-ISSN: 23249250
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  • 4
    Language: English
    In: Eos, Transactions American Geophysical Union, 2000, Vol.81(11), p.113
    Description: The Field Integrated Design and Operations (FIDO) Rover, a prototype vehicle designed to rehearse operations for the Mars Sample Return missions and associated Athena Rover, was put through a suite of field trials in the Silver Lake area of the Mojave Desert in April and October 1999. The trials also provided an opportunity to foster active involvement of students in rover missions using inquiry‐based study An integrated team of more than two dozen high school students and their teachers from Los Angeles, Phoenix, Ithaca, and St. Louis (LAPIS) developed and implemented their own FIDO‐based rover mission that employed long‐distance traverses to explore terrains and make discoveries. LAPIS team members from each city were paired with local science mentors who are part of the Athena Science Team to ensure that the LAPIS activities furthered the overall mission objectives at Silver Lake and to provide expert advice.The students learned to work as a geographically distributed team, developed hypotheses to test, commanded the rover via the Internet to test their hypotheses, analyzed data, and generated their own Web site and archives. Post‐LAPIS assessments demonstrated that the participants gained new communication and information technology skills, an enhanced ability to cut across traditional disciplines to solve problems, and a greater understanding of planetary exploration and discovery Further, for some of the students, LAPIS provided the right set of experiences needed to help them define specific career goals in science, mathematics, and engineering.
    Keywords: Extraterrestrial Geology ; Athena Science Payload ; Education ; Field Studies ; K-12 Education ; Mars ; Planetology ; Planets ; Rovers ; Samples ; Sampling ; Simulation ; Terrestrial Planets;
    ISSN: 0096-3941
    E-ISSN: 23249250
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