Browsing by Author "Urbina, Julio"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Restricted A radio science perspective on long-duration meteor trails(American Geophysical Union, 2007-12-27) Malhotra, Akshay; Mathews, John D.; Urbina, JulioNonclassical radar meteor echoes or range spread trail echoes (RSTEs), lasting from tens of seconds to over 15 min, have been a subject of considerable interest and speculation in the community ever since they were first observed in the 1940s. Using data collected from the Jicamarca Radio Observatory 50 MHz VHF radar in June 2006, we find that many properties of RSTEs can be explained largely from a radio science perspective. On a statistical basis, RSTEs of duration >15 s are observed exclusively from scatterers in the k⊥B (k = radar wave number; B = geomagnetic field) region apparently as the result of trail evolution parallel to B, forming approximately Fresnel-zone sized scattering regions thus narrowing the scattering pattern. This result implies that the initial irregularity structures in the meteor trail exhibit a wide scattering pattern that can be seen from anywhere in the radar beam given sufficient radar sensitivity but once the trail significantly elongates along B, it can be detected only from the k⊥B region of the radar. This conclusion has far-reaching implications to current interpretations of instability development in RSTEs as the location of the meteoroid trajectory relative to the narrow k⊥B region strongly determines observed RSTE properties such as onset time relative to the head echo and trail lifetime as functions of altitude. That is, a RSTE event viewed by two closely spaced identical radars would have different properties. Meteoroid size, energy, and fragmentation as well as radar properties such as frequency, beam pattern, and absolute sensitivity play obvious roles as well.Item Restricted Aspect sensitivity considerations in interpreting radar meteor range-spread trail echo durations(Springer, 2007-12) Malhotra, Akshay; Mathews, John D.; Urbina, JulioInitial results from June 2006 50 MHz radar campaigns at the Jicamarca Radio Observatory (JRO) reveal that full understanding of Range-Spread Trail Echoes (RSTEs) must involve knowledge of the trail viewing angle relative to kB (radar pointing direction perpendicular to the geomagnetic field) as a function of location along the meteoroid trajectory. A study of RSTEs using the JRO main array demonstrates that an overwhelming majority of long duration ([15 s) trails occur in the kB region of the radar. Short duration (5 s) trails constitute a large majority of the trails and are seen throughout the illuminated volume although with a statistically significant kB preference indicating that observed trail duration is also a function of factors such as meteoroid mass and energy. Given the apparent radar scattering aspect sensitivity of the trail plasma as it expands parallel to the geomagnetic field, we hypothesize that short duration echoes away from the kB zone might be longer duration echoes if viewed from the correct geometry. We conclude that an RSTE event viewed by two closely spaced identical radars would exhibit different properties due to the differing viewing angles. Meteoroid size, energy, and fragmentation as well as radar properties such as frequency, beam pattern, and absolute sensitivity play obvious roles as well.Item Open Access Effect of meteor ionization on sporadic-E observed at Jicamarca(American Geophysical Union, 2008-08-09) Malhotra, Akshay; Mathews, John D.; Urbina, JulioRelatively little progress has been made in the study of equatorial Sporadic-E when compared to the study of mid-latitude Sporadic-E. Indeed, it is unclear if Sporadic-E has been observed at all near the geomagnetic equator using any technique other than the ionosonde. In particular, there have been no reports of Sporadic-E observed using the Jicamarca Radio Observatory (JRO) 50 MHz radar. The overwhelming—in SNR terms—presence of the nearly ubiquitous Equatorial Electrojet (EEJ) is the likely reason Sporadic-E has not been reported at JRO as well as at other similar radars near the geomagnetic equator. We present here what we believe to be the first Sporadic-E (defined here as altitude-narrow E-region layers that last tens of minutes) observations from JRO. The structure and characteristics of these equatorial Sporadic-E layers is compared with their mid-latitude counterparts. We also demonstrate the immediate effect of meteor-produced ionization on the formation and evolution of the equatorial Sporadic-E layers.Item Open Access El radar VHF perfilador de vientos de la estación Antártica Machu-Picchu(Pontificia Universidad Católica del Perú, 1994) Sarango, Martín; Urbina, Julio; Woodman Pollitt, Ronald Francisco; Ragaini, Enrico; Vásquez, EdilbertoEl propósito de este artículo es dar a conocer el sistema radar MST instalado en la Estación Científica Antártica Machu-Picchu. La concepción, diseño y desarrollo del instrumento (radar) es producto íntegro de la ingeniería peruana. Se presta especial atención al novedoso sistema de procesamiento de datos implementado, que constituye la primera aplicación con Procesadores Digitales de Señales (DSP por sus siglas en inglés) desarrollada en el Perú. Su diseño es totalmente original e innovador frente a los sistemas que actualmente operan en todo el mundo, alcanzando, e incluso superando las capacidades de procesamiento de muchos de ellos. Así mismo se hace una presentación de datos típicos recogidos con el instrumento, y una breve discusión sobre los primeros resultados obtenidos.Item Restricted First steps toward the implementation of a cognitive radar to study plasma instabilities along the magnetic equator(American Geophysical Union, 2015-03) Sorbello, Robert; Urbina, Julio; Stephens, ZachCognitive radar is envisioned to be the future of remote-sensing systems. The idea proposed by details that a cognitive radar will have the ability to learn about the sensing environment and, over time, optimize returns from targets of interest by altering the transmitted pulse waveform. This paper focuses on the first step of the cognitive process for ionospheric radar observations in the equatorial region. In this region, three plasma irregularities are observed very regularly via radar, namely, Spread F, 150 km echoes, and electrojet. During real-time observations, the first step of the cognitive process entails automatically recognizing the current plasma instability forming in the ionosphere. A preliminary test for the detection and classification of these events is performed off-line using radar observations from the Jicamarca Radio Observatory, located in Lima, Peru. The chosen classification process utilizes a supervised learning algorithm (Expectation-Maximization) to generate a probability distribution function (Gaussian Mixture Model) for each plasma instability based on certain measurable criterion. This paper outlines the training and classification process with the resulting cross validation performance subsequently reported. Results demonstrate the effectiveness of the chosen classifier because of the high cross validation and minimal misclassifications of the events.