Browsing by Author "Mathews, J. D."
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Item Restricted High-altitude meteors and meteoroid fragmentation observed at the Jicamarca Radio Observatory(Royal Astronomical Society, 2014-12-08) Gao, B.; Mathews, J. D.Modern high-power, large-aperture (HPLA) radars have been used in a variety of investigations including the investigation of meteoroid fragmentation. The identification of fragmentation has been based on a detailed interpretation, based on radio science, of head- and trail-echo properties. We now extend the discussion of fragmenting meteoroids to include apparent high-altitude (130–180 km) meteors observed at the Jicamarca Radio Observatory (JRO). While there have been a few reports of high-altitude meteors observed both optically and with radar, the meteor radar community has remained sceptical, with suspicions of antenna side-lobe contamination being the most commonly raised objection. We report results from two sets of meteor observations carried out at JRO in 2010 April. Our findings include meteoroid fragmentation results that are similar to those from the Arecibo VHF radar. These findings lead to the conclusions that fragmentation is not only observed at the JRO but that k⊥B scattering adds an interesting additional radio science dimension to the issue. We also report on apparent high-altitude meteor events that, if ultimately confirmed, offer insight into sputtering as a source of the meteor ionization, and perhaps indicate the unique importance of magnetic field geometry in these head-echo observations. Also, new, apparently high-altitude transient events, likely related to the meteoroid flux, have been identified. In presenting these results, we note our careful calibration of the JRO radar, utilizing satellite returns in order to largely, if not totally, exclude side-lobe contamination and other possible error sources, as reported in our companion paper.Item Restricted Phase and pattern calibration of the Jicamarca Radio Observatory radar using satellites(Royal Astronomical Society, 2014-12-08) Gao, B.; Mathews, J. D.The Jicamarca Radio Observatory (JRO) main 50-MHz array antenna radar system with multiple receivers is being used to study meteors via two interferometric receiving modes. One of the major challenges in these studies is the phase calibration of the various receiver (interferometric) channels (legs). While investigating some ambiguous features in meteor head-echo results, we developed a ‘new’ calibration technique that employs satellite observations to produce more accurate phase and pattern measurements than were previously available. This calibration technique, which resolves head-echo ambiguities, uses the fact that Earth-orbiting satellites are in gravitationally well-defined orbits and thus the pulse-to-pulse radar returns must be consistent (coherent) for an entire satellite pass through the radar beam. In particular, the satellite yields a reliable point source for phase and thus interferometry-derived range, Doppler and trajectory calibration. Using several satellites observed during standard meteor observations, we derive satellite orbital parameters by matching the observed and modelled three-dimensional trajectory and Doppler results. This approach uncovered subtle phase distortions that led to interferometry-derived trajectory distortions that are important only to point targets such as meteor head-echoes. We present the array calibration and radar imaging of satellite passes from our meteor observations of 2010 April 15/16. Future observations of a priori known satellites would likely yield significantly more accurate calibrations, especially of distant side lobes.Item Restricted Range-Doppler mapping of space-based targets using the JRO 50 MHz radar(Springer, 2017-12-02) Kesaraju, S.; Mathews, J. D.; Milla, Marco; Vierinen, J.The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna segment during lunar transit over JRO. Dual-linear polarization receive systems were employed on two quarter-array segments and on two 1/64th array modules giving the longest possible baselines across the transit path. A Range-Doppler mapping technique that uses the rotational motion of the targets and an autofocusing motion and ionospheric delay compensation technique has been implemented to generate the two-dimensional maps of the point-target (Satellite) and range-spread target (Moon). A review of our technique and the maps obtained from these observations is presented herein. Range-Doppler maps of the Moon and satellites are instructive with regards to possible further improvement of the technique, especially regarding ionospheric compensation.