Browsing by Author "Galindo, F. R."
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Item Open Access Comparing F region ionospheric irregularity observations from C/NOFS and Jicamarca(American Geophysical Union, 2009-07-11) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Observations of plasma density irregularities associated with equatorial spread F (ESF) have been made using the Jicamarca Radio Observatory and the Plasma Langmuir Probe (PLP) and Vector Electric Field Instrument (VEFI) instruments on the Communications Navigation Outage Forecast System (C/NOFS) satellite during a close spatio-temporal conjunction. The radar data resolution is of the order of 1 km and a few sec. in space and time, respectively. We find that coherent scatter intensifications at these scales are coincident and collocated with plasma density depletions as determined by C/NOFS. The Doppler shifts of the localized echoes are also comparable to the vertical components of the E × B plasma drifts. The strongest backscatter does not necessarily come from the deepest or most rapidly convecting depletions. This implies a complex relationship between coherent backscatter and the underlying state parameters in the ionospheric plasma.Item Open Access Comparing Jicamarca and C/NOFS (PLP, VEFI): observations of equatorial spread F irregularities(Instituto Geofísico del Perú, 2009) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Diapositivas presentadas en The Meeting of the Americas, 2009 Joint Assembly, organizadas por la American Geophysical Union del 24 al 27 mayo de 2009 en Ontario, Canada.Item Open Access Equatorial ExB drifts during sudden stratospheric warming events(Instituto Geofísico del Perú, 2009) Chau Chong Shing, Jorge Luis; Galindo, F. R.; Fejer, B. G.; Goncharenko, L. P.Diapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Open Access Evaluation of topside equatorial spread F spectra estimators using Monte Carlo simulations(Instituto Geofísico del Perú, 2008) Galindo, F. R.; Kuyeng, K. M.; Chau Chong Shing, Jorge Luis; Hysell, D. L.Radar observations typically employ periodic pulses to study any target. This scheme allows a simple processing of the data but the results frequently shows range or frequency aliasing. In order to solve this problem Uppala and Sahr [1] introduced the aperiodic technique (AT) in the radio science community. The AT is based on transmitting pulses at non uniform intervals and allows to study moderately overspread targets. Some equatorial Spread F (ESF) echoes belong to this category, particularly those from the topside. Using this idea Jicamarca Radio Observatory (JRO) has done a couple of experiments to study ESF echoes. Chau et al [2] used the Fast Fourier Transform (FFT) to compute spectra from those experiments and developed some criteria to remove clutter due to the aperiodic sequence. A second scheme of work was introduced by Hysell et al [3] and this scheme uses a Bayesian method to compute the spectra. Continuing this line of research a Monte Carlo simulations of typical echoes from equatorial ionospheric irregularities as well as ground clutter has been done to evaluate different aperiodic pulsing and inversion techniques to estimate the spectra or its corresponding AutoCorrelation Function (ACF). Our main objective is the estimation of the moderately overspread topside equatorial spread F (ESF) spectra. The optimal spectra estimators combined with radar imaging techniques might represent the unique means to estimate the irregularity power and energy spectral density versus wavenumber from the ground.Item Open Access On the characterization of radar receivers for meteor-head echoes studies(American Geophysical Union, 2013-01) Galindo, F. R.; Urbina, J.; Chau Chong Shing, Jorge Luis; Dyrud, L.; Milla, MarcoWe report the role that the ambiguity function (AF) plays on the determination of signal to noise ratio (SNR) collected from meteor head echoes. Theoretical analysis shows that any measured meteor SNR exhibits temporal ripples whose shape is related to both the transmitted pulse envelope and the filter impulse response of the receiver. These theoretical findings are corroborated with (1) experimental meteor data recorded with Jicamarca 50 MHz radar (11.95 S, 76.87 W) and (2) simulated meteor data obtained by replicating the acquisition system of Jicamarca. A statistical analysis of the experimental meteor data reveals that at least 14% of the population collected each day at Jicamarca exhibits these ripples. On the remaining 86% of meteor events, the ripples cannot be distinguished due to noise, contamination from other sources of scattering (i.e., nonspecular echoes), and ensemble average applied to the data. In general, these ripples demonstrate the importance of obtaining an accurate model of a radar system to avoid misinterpretation of SNR.Item Open Access Phase calibration approaches for radar interferometry and imaging configurations: equatorial spread F results(European Geosciences Union, 2008-08) Chau Chong Shing, Jorge Luis; Hysell, D. L.; Kuyeng, K. M.; Galindo, F. R.In recent years, more and more radar systems with multiple-receiver antennas are being used to study the atmospheric and ionospheric irregularities with either interferometric and/or imaging configurations. In such systems, one of the major challenges is to know the phase offsets between the different receiver channels. Such phases are intrinsic to the system and are due to different cable lengths, filters, attenuators, amplifiers, antenna impedance, etc. Moreover, such phases change as function of time, on different time scales, depending on the specific installation. In this work, we present three approaches using natural targets (radio stars, meteor-head and meteor trail echoes) that allow either an absolute or relative phase calibration. In addition, we present the results of using an artificial source (radio beacon) for a continuous calibration that complements the previous approaches. These approaches are robust and good alternatives to other approaches, e.g. self-calibration techniques using known data features, or for multiple-receiver configurations constantly changing their receiving elements. In order to show the good performance of the proposed phase calibration techniques, we present new radar imaging results of equatorial spread F (ESF) irregularities. Finally we introduce a new way to represent range-time intensity (RTI) maps color coded with the Doppler information. Such modified map allows the identification and interpretation of geophysical phenomena, previously hidden in conventional RTI maps, e.g. the time and altitude of occurrence of ESF irregularities pinching off from the bottomside and their respective Doppler velocity.Item Open Access The equatorial ionosphere over Jicamarca during the January 2009 sudden stratospheric warming(Instituto Geofísico del Perú, 2009) Chau Chong Shing, Jorge Luis; Galindo, F. R.; Milla, Marco; Kudeki, E.; Reyes, P. M.; Goncharenko, L. P.; Fejer, B. G.Diapositivas presentadas en 2009 Joint Assembly. The Meeting of the Americas. 24-27 May 2009. Toronto, Ontario, Canada.