Browsing by Author "Chau Chong Shing, Jorge Luis"
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Item Restricted 150-km echoes and their relevance to aeronomy(Instituto Geofísico del Perú, 2013-06) Chau Chong Shing, Jorge LuisPonencia presentada en the CEDAR Workshop , Boulder, Colorado, USA, June 24, 2013.Item Open Access A high-resolution study of mesospheric fine structure with the Jicamarca MST radar(European Geosciences Union (EGU), 2006-07-03) Sheth, R.; Kudeki, E.; Lehmacher, G.; Sarango, M.; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Guo, L.; Reyes, P.Correlation studies performed on data from recent mesospheric experiments conducted with the 50-MHz Jicamarca radar in May 2003 and July 2004 are reported. The study is based on signals detected from a combination of vertical and off-vertical beams. The nominal height resolution was 150 m and spectral estimates were obtained after ~1 min integration. Spectral widths and backscattered power generally show positive correlations at upper mesospheric heights in agreement with earlier findings (e.g., Fukao et al., 1980) that upper mesospheric echoes are dominated by isotropic Bragg scatter. In many instances in the upper mesosphere, a weakening of positive correlation away from layer centers (towards top and bottom boundaries) was observed with the aid of improved height resolution. This finding supports the idea that layer edges are dominated by anisotropic turbulence. The data also suggests that negative correlations observed at lower mesospheric heights are caused by scattering from anisotropic structures rather than reflections from sharp vertical gradients in electron density.Item Restricted A multi-beam incoherent scatter radar technique for the estimation of ionospheric electron density and Te/Ti profiles at Jicamarca(Elsevier, 2013-12) Milla, Marco; Kudeki, Erhan; Reyes, Pablo M.; Chau Chong Shing, Jorge LuisA multi-beam incoherent scatter radar technique has been developed at the Jicamarca Radio Observatory in order to maximize the number of ionospheric parameters that can be estimated simultaneously. The technique interleaves radar observations with antenna beams pointing perpendicular and oblique to the Earth's magnetic field. For the estimation of the ionospheric parameters, we have modeled the magnetic aspect angle variations of the signal power and cross-correlation data measured in multiple directions. The data model, formulated in terms of soft-target radar equations, was built based on the theories of incoherent scattering and magneto-ionic propagation. Applying a nonlinear least-squares inversion algorithm, we have succeeded in measuring simultaneously ionospheric electron densities Ne, electronto-ion temperature ratios Te=Ti as well as vertical and zonal plasma drifts. In the past, radar users had to choose between either perpendicular-to-B or oblique modes, thus, the application of this technique extends the current capabilities of the Jicamarca radar.Item Restricted A statistical comparison of horizontal winds obtained by a variety of spaced antenna techniques using the Jicamarca VHF radar(American Geophysical Union, 1998-11) Chau Chong Shing, Jorge Luis; Balsley, Ben B.We have used the Jicamarca radar system to measure horizontal winds by a variety of time domain and frequency domain spaced antenna techniques. Horizontal wind comparisons for two orthogonal components are carried out in a statistical sense, i.e., using correlation coefficients, mean differences, standard deviation of differences, and percentage of failures. We find that a simple technique that assumes horizontally isotropic scattering compares very closely with the more complicated full correlation analysis techniques. Techniques that attempt to correct for turbulence appear to be very sensitive to the way we estimate the width of the cross‐correlation/spectra functions. This is particularly true above 15 km, where discrepancies in the wind speed are apparent. In general, all techniques give essentially the same wind direction.Item Restricted A statistical comparison of VHF techniques to study clear-air vertical velocities in the lower atmosphere using the Jicamarca radar(American Geophysical Union, 1998-11) Chau Chong Shing, Jorge Luis; Balsley, Ben B.We compare two types of VHF vertical velocity measurement techniques using a special configuration of the Jicamarca 50-MHz radar antenna. Zenith (vertically directed single-beam) techniques and spaced antenna (SA) techniques are compared using a 54-hour concurrent data set. We compare two different zenith techniques using different antenna beam widths (0.85° and 3.5°). In addition, we compare vertical velocities measured by a “quasi” Doppler beam swinging (QDBS) technique and a SA approach that incorporate either “inferred” or “corrected” vertical velocities. All of the results are compared in terms of statistical basis. Results are presented for both quiet (low wind, low variability) and active (high wind, high variability) conditions. We use the results of the narrow-beam zenith technique as a reference profile and discuss its validity as a reference. Our comparisons show that relative to the reference, (1) the use of corrected values (i.e., correcting for horizontal leakage) gives better results than the wide-beam zenith technique, although mean differences of ∼−3 and ∼4 cm s−1 are still observed below 12 and above 15 km, respectively, (2) QDBS results give the closest mean value agreement of all the techniques, and (3) most of the vertical velocity discrepancies are seen as variations in the mean values.Item Open Access Actividades del Radio Obsevatorio de Jicamarca: respuestas a preguntas frecuentes(Instituto Geofísico del Perú, 2009-08) Chau Chong Shing, Jorge LuisPonencia presentada por investigadores del Instituto Geofísico del Perú.Item Restricted Altitudinal dependence of evening equatorial F region vertical plasma drifts(American Geophysical Union, 2014-06-06) Fejer, B. G.; Hui, D.; Chau Chong Shing, Jorge Luis; Kudeki, E.We use Jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial F region vertical plasma drifts. We also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km. These data show that the afternoon drifts decrease weakly with altitude. Near their evening prereversal enhancements, the vertical drifts generally increase with altitude below about the F layer peak, decrease with height near the F layer peak and above, and are nearly height independent in the (solar flux dependent) topside ionosphere. The transition altitudes from height‐decreasing to height‐independent evening upward drifts decrease with altitude from solar maximum to solar minimum. After their reversal to downward, the vertical drifts do not change much with height. The altitudinal dependence of the evening vertical drifts has large day‐to‐day variability and is closely related to the time dependence of the zonal drifts, as expected from the curl‐free electric field condition.Item Open Access AMISR contributions to equatorial aeronomy(Instituto Geofísico del Perú, 2004) Hysell, D. L.; Chau Chong Shing, Jorge LuisPresentación incluida en CEDAR (Coupling, Energetics and Dynamics of Atmospheric Regions) Workshop for 2004 (Santa Fe, Nuevo México, 2004).Item Open Access An imaging interferometry capability for the EISCAT Svalbard Radar(European Geosciences Union (EGU), 2005-01-31) Grydeland, Tom; Chau Chong Shing, Jorge Luis; La Hoz, C.; Brekke, A.Interferometric imaging (aperture synthesis imaging) is a technique used by radio astronomers to achieve angular resolution that far surpasses what is possible with a single large aperture. A similar technique has been used for radar imaging studies of equatorial ionospheric phenomena at the Jicamarca Radio Observatory. We present plans for adding an interferometric imaging capability to the EISCAT Svalbard Radar (ESR), a capability which will contribute significantly to several areas of active research, including naturally and artificially enhanced ion-acoustic echoes and their detailed relation in space and time to optical phenomena, polar mesospheric summer echoes (PMSE), and meteor studies. Interferometry using the two antennas of the ESR has demonstra ted the existence of extremely narrow, field-aligned scattering structures, but having only a single baseline is a severe limitation for such studies. Building additional IS-class antennas at the ESR is not a trivial task. However, the very high scattering levels in enhanced ion-acoustic echoes and PMSE means that a passive receiver antenna of more modest gain should still be capable of detecting these echoes. In this paper we pre sent simulations of what an imaging interferometer will be capable of observing for different antenna configurations and brightness distributions, under ideal conditions, using two different image inversion algorithms. We also discuss different antenna and receiver technologies.Item Open Access An upper bound on the solar radar cross section at 50 MHz(American Geophysical Union, 2006-04) Coles, W.A.; Harmon, J. K.; Sulzer, M. P.; Chau Chong Shing, Jorge Luis; Woodman Pollitt, Ronald FranciscoWe have made 16 unsuccessful attempts, in February and October 2003, and February 2004, to observe solar echoes using the 50 MHz radar at Jicamarca in Peru. The upper bound that we have determined on the solar cross section is significantly lower than the average of earlier reported observations. In this paper we will describe the observations, discuss the noise and interference from solar bursts, and suggest possible reasons why the echo might be weaker than expected.Item Open Access Antenna compression using binary phase coding(American Geophysical Union, 2001-01-01) Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge LuisWe introduce the first antenna “compression” scheme for coherent radars. The idea is to transmit with a large array of phase‐coded antennas at full power and later synthesize by linear superposition and proper phasing, the equivalent of a small transmitting antenna, similar to a single antenna module of the array. The full “decoding” is done by software by adding the power and cross‐power estimates of the signals of each code, so no extra burden is added other than the summations. This approach allows the use of all the available power in phased array systems where either high‐power transmitters cannot be used with small antennas or the transmitted power is distributed among the antenna elements. The wider beams are particularly important in meteor systems and, recently, in some radar studies of the neutral atmosphere, especially when multiple receiving antennas are used. Our scheme is based on complementary binary phase coding of antenna elements and works in a similar fashion to complementary phase coding used in pulse compression. We have implemented this idea at the Jicamarca Radio Observatory using a two‐dimensional approach; thus four two‐dimensional complementary codes were derived. The performance of this implementation has been tested using imaging techniques on an interferometer of four receiving antenna modules to study the angular characteristics of the well‐known equatorial electrojet irregularities. In addition, in this mode we have made successful observations of the upper troposphere and lower stratosphere.Item Open Access Antenna compression using binary phase coding: an imaging application(Instituto Geofísico del Perú, Radio Observatorio de Jicamarca, 2000) Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge LuisVery often one has a radar experiment with a conflicting demand. On the one hand one would like to illuminate the target with all the high power usually available with a big antenna; but on the other hand one would also like to have the broadest beam possible (i.e., smallest antenna section). Usually both situations are not compatible and one has to compromise one for the other. This problem is present, for instance, when one has a phased array with a single high power transmitter (e.g., the Jicamarca Incoherent scatter radar), where the total high power cannot be transmitted with single antenna elements. A even stronger constrain is present if one has a phased array with distributed transmitters (e.g., the Middle and Upper atmosphere (MU) VHF radar in Japan or the Buckland Park MF radar in Australia). Normally, for a given installation, i.e., fixed transmitter power level per module, and fixed number of modules (antenna size), going to smaller antennas not only implies broader antenna beams, but unfortunately also a reduction on the total transmitter power. In this paper we present a solution to overcome this limitation, i.e., transmit with a wide beam and all the available power. Our scheme is based on complementary binary phase coding of the antenna elements in a similar fashion to phase coding used in pulse compression [e.g., Farley, 1985]. The decoding part is done by software by adding the statistics of each of the coded signal, so no extra burden is added to the processing other than a few summations.Item Restricted Aperture synthesis radar imaging for upper atmospheric research(IntechOpen, 2012-04) Hysell, D. L.; Chau Chong Shing, Jorge LuisRadars used for upper-atmospheric applications can be engineered to measure the Doppler spectra of their targets adequately for most intents and purposes, the spectral resolution being limited only by the observing time and the constraints of stationarity. Likewise, they can measure the range to their targets adequately for most intents and purposes, range resolution being limited by system bandwidth, the power budget, and the constraints of stationarity. Problems arise for “overspread” targets, where range and frequency aliasing cannot simultaneously be avoided using pulse-to-pulse methodologies, and more complicated pulse-to-lag or aperiodic pulsing methods are required (see for example (Farley, 1972; Huuskonen et al., 1996; Lehtinen, 1986; Sulzer, 1986; Uppala, 1993)). Important examples of this situation include incoherent scatter experiments (Farley, 1969), observations of meteor head echoes (Chau & Woodman, 2004), and observations of plasma density irregularities present in certain rapid flows, as are found in the equatorial ionosphere during so-called “equatorial spread F” (Woodman, 2009; Woodman & La Hoz, 1976).Item Open Access Bottom-type scattering layers and equatorial spread F(European Geosciences Union (EGU), 2004-12) Hysell, D. L.; Chun, J.; Chau Chong Shing, Jorge LuisJicamarca radar observations of bottom-type coherent scattering layers in the post-sunset bottomside F-region ionosphere are presented and analyzed. The morphology of the primary waves seen in radar images of the layers supports the hypothesis of Kudeki and Bhattacharyya (1999) that wind-driven gradient drift instabilities are operating. In one layer event when topside spread F did not occur, irregularities were distributed uniformly in space throughout the layers. In another event when topside spread F did eventually occur, the irregularities within the pre-existing bottom-type layers were horizontally clustered, with clusters separated by about 30 km. The same horizontal periodicity was evident in the radar plumes and large-scale irregularities that emerged later in the event. We surmise that horizontal periodicity in bottom-type layer irregularity distribution is indicative of large-scale horizontal waves in the bottomside F-region that may serve as seed waves for large-scale Rayleigh Taylor instabilities.Item Open Access Calibrated radar observations of the equatorial mesosphere and ionosphere during an 11-day campaign(Instituto Geofísico del Perú, 2009) Kudeki, E.; Milla, Marco; Reyes, P.; Lehmacher, G.; Chau Chong Shing, Jorge Luis; Kuyeng, K. M.; De la Jara, CésarPresentado en MST12 - 12th Workshop on Technical and Scientific Aspects of MST Radars, London, Ontario, Canada, 17-23 May 2009.Item Restricted Caracterización de meteoros, utilizando el radar VHF del Radio Observatorio de Jicamarca durante la presencia de ecos coherentes de electrochorro ecuatorial(Universidad Nacional de Ingeniería, 2007) Galindo Palomino, Freddy Ronald; Chau Chong Shing, Jorge LuisEn el presente trabajo de tesis se ha desarrollado un conjunto de algoritmos que permiten realizar la caracterización de ecos de meteoros en presencia o ausencia de ecos de electrochorro ecuatorial y/o ecos no especulares de meteoros. Esta técnica desarrollada es agresiva para ubicar ecos de meteoros y determinar los principales parámetros que permiten caracterizarlos. La técnica basa su funcionamiento en un proceso de selección manual, otorgándole al operario la decisión final de definir entre un eco de meteoro y un eco que no es de meteoro, para posteriormente determinar cada uno de los parámetros del meteoro (e.g., velocidad radial, rango inicial). Adicionalmente al proceso de caracterización, se analizaron técnicas para la remoción de ecos del electrochorro ecuatorial. Cabe resaltar, que justamente una de estas técnicas ha permitido identificar automáticamente más del 90% de los meteoros caracterizados manualmente. Los resultados obtenidos, permiten sentar la base para un futuro algoritmo automático. La validación de esta nueva herramienta para el procesamiento de ecos de meteoros, se ha realizado comparando los parámetros obtenidos en el experimento realizado el día 19 de Noviembre del 2002 y procesado con una técnica antigua (proceso automático conservador), con los parámetros obtenidos en el experimento realizado los días 22 y 23 de Noviembre del 2005 y procesado con los algoritmos desarrollados en esta tesis (proceso manual). Los resultados obtenidos muestran un incremento en el número de meteoros observados, especialmente para tiempos donde el EEJ está presente. Se detectó un mayor número de meteoros de baja velocidad y se encontraron nuevas poblaciones de meteoros . La velocidad determinada de pulso a pulso mostró una diferencia menor a 2 km/s respecto a la velocidad obtenida del ajuste lineal del Rango vs. Tiempo. Adicionalmente, esta nueva técnica posibilita un análisis cuidadoso de cada meteoro. Todas estas características son ejemplos de la utilidad de esta nueva herramienta para el procesamiento de ecos de meteoros.Item Restricted CEDAR Electrodynamics Thermosphere Ionosphere (ETI) Challenge for systematic assessment of ionosphere/thermosphere models: NmF2, hmF2, and vertical drift using ground‐based observations(American Geophysical Union, 2011-12-31) Shim, J. S.; Kuznetsova, M.; Rastätter, L.; Hesse, M.; Bilitza, D.; Butala, M.; Codrescu, M.; Emery, B.; Foster, B.; Fuller-Rowell, T.; Huba, J.; Mannucci, A. J.; Pi, X.; Ridley, A.; Scherliess, L.; Schunk, R. W.; Stephens, P.; Thompson, D. C.; Zhu, L.; Anderson, D.; Chau Chong Shing, Jorge Luis; Sojka, J. J.; Rideout, B.Objective quantification of model performance based on metrics helps us evaluate the current state of space physics modeling capability, address differences among various modeling approaches, and track model improvements over time. The Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR) Electrodynamics Thermosphere Ionosphere (ETI) Challenge was initiated in 2009 to assess accuracy of various ionosphere/thermosphere models in reproducing ionosphere and thermosphere parameters. A total of nine events and five physical parameters were selected to compare between model outputs and observations. The nine events included two strong and one moderate geomagnetic storm events from GEM Challenge events and three moderate storms and three quiet periods from the first half of the International Polar Year (IPY) campaign, which lasted for 2 years, from March 2007 to March 2009. The five physical parameters selected were NmF2 and hmF2 from ISRs and LEO satellites such as CHAMP and COSMIC, vertical drifts at Jicamarca, and electron and neutral densities along the track of the CHAMP satellite. For this study, four different metrics and up to 10 models were used. In this paper, we focus on preliminary results of the study using ground‐based measurements, which include NmF2 and hmF2 from Incoherent Scatter Radars (ISRs), and vertical drifts at Jicamarca. The results show that the model performance strongly depends on the type of metrics used, and thus no model is ranked top for all used metrics. The analysis further indicates that performance of the model also varies with latitude and geomagnetic activity level.Item Open Access Characteristics of low latitude backscatter from ionospheric E region and F region field-aligned irregularities obtained with the Piura VHF radar(Instituto Geofísico del Perú, 2003) Chau Chong Shing, Jorge Luis; Woodman Pollitt, Ronald Francisco; Flores, L.A.We present a summary ofthe characteristics of echoes from ionospheric (E and F region) field-aligned irregularities obtained with the Piura VHF radar (~7.0° dip latitude, outside the equatorial electrojet region). Our results are based on (1) intermittent monostatic observations made between 1991 and 1999, (2) continuous monostatic observations made between January 2000 and June 2001, and (3) intermittent interferometric observations since August 2001. Among other important results, we have found that the E-region echoes are stronger and occur more frequently during local summer. In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence oftopside ESF irregularities over Jicamarca.Item Open Access Climatology of postsunset equatorial spread F over Jicamarca(American Geophysical Union, 2009-07) Chapagain, Narayan P.; Fejer, Bela G.; Chau Chong Shing, Jorge LuisWe use radar observations from 1996 to 2006 to study the climatology of postsunset equatorial 3-m spread F irregularities over Jicamarca during all seasons. We show that the spread F onset times do not change with solar flux and that their onset heights, which occur near the altitude of the evening F region velocity vortex, increase linearly from about 260 to 400 km from solar minimum to solar maximum. Higher onset heights generally lead to stronger radar echoes. During the equinox, spread F onset occurs near vertical drift evening reversal times, while during the December solstice, they occur near the drift reversal times close to solar minimum and near the time of the prereversal velocity peak for high solar flux conditions. On average, radar plume onset occurs earlier with increasing solar flux in all seasons. Plume onset and peak altitudes increase with solar activity, and the peak heights are generally highest during the equinox. The F region upward drift velocities that precede spread F onset increase from solar minimum to solar maximum and are approximately proportional to the maximum prereversal drift peak velocities.Item Restricted Coherent MIMO to improve aperture synthesis radar imaging of field-aligned irregularities: first results at Jicamarca(Institute of Electrical and Electronics Engineers, 2018) Urco, Juan M.; Chau Chong Shing, Jorge Luis; Milla, Marco; Vierinen, Juha P.; Weber, TobiasMultiple-input multiple-output (MIMO) radar techniques make use of multiple transmitters and multiple receivers to improve the spatial characterization of targets. In the case where the Bragg scattering k → -vector can be assumed to be the same for all transmit-receive paths, MIMO methods can be seen as a way of increasing the number of effective receivers. In the last decades, there has been scientific interest in determining the spatial characteristics of ionospheric and atmospheric irregularities on the subtransmit beam scale, allowing the study of processes in their intrinsic scales, otherwise inaccessible using simple beamforming techniques. Interferometric methods, including aperture synthesis imaging, were used in the past with a single transmitter and multiple receivers [single-input multiple-output (SIMO)]. In this paper, we present the first implementation of MIMO techniques to improve the spatial resolution of aperture synthesis radar imaging of daytime equatorial electrojet irregularities observed using the Jicamarca Radio Observatory (JRO). Our implementation uses two spatially separated transmitters and four spatially separated receivers. In order to separate the contributions of each transmitter, time, code, and polarization diversity experiments have been tested. We find that all three diversity approaches can be used for ionospheric irregularities, but time and polarization diversity are not applicable in all situations due to the range and Doppler width of the echoes, and due to magnetoionic radio propagation effects. The results are evaluated by comparing new MIMO imaging results against the currently used SIMO imaging technique. We present and discuss the theoretical and practical aspects of the MIMO approach, so they can be applied to study other targets not only at JRO but also at other modular coherent scatter radars.