Browsing by Author "Woodman Pollitt, Ronald Francisco"
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Item Restricted A causal relationship between lightning and explosive spread F(American Geophysical Union, 1984-12) Woodman Pollitt, Ronald Francisco; Kudeki, ErhanExperimental evidence for a causal relationship between lightning and explosive equatorial spread F is presented. It is proposed that explosive spread F is produced by rapidly growing plasma instabilities, which are triggered by sudden increases of the F region ambient electric fields due to the penetration of lightning fields into regions of weak or marginal instability.Item Restricted A coherent integrator-decoder preprocessor for the SOUSY-VHF-Radar(American Geophysical Union, 1980-03) Woodman Pollitt, Ronald Francisco; Kugel, R.P.; Röttger, J."The 53.5-MHz radar of the Max-Planck-Institut für Aeronomie (SOUSY-VHF-Radar) was specifically designed for the study of the dynamics of the troposphere, stratosphere, and mesosphere including turbulence and other small-scale phenomena. Transmitter and receivers were designed for a pulse width and altitude resolution of the order of 75–150 m. Such high resolution corresponds to sampling rates of the order of 2 million complex samples per second. Maximum sensitivity calls for the use of coded pulse schemes (pulse compression). The digital decoding and processing requirements of such a high information rate are beyond the capabilities of a general purpose digital computer and demanded a special purpose preprocessor. A programable preprocessor was designed and built, and it is the subject of this paper. It can decode an arbitrary sequence and perform coherent integrations for as many as 1024 altitudes. The coherent integration reduces the data rate into the computer to reasonable values. Also, by performing the coherent integration before decoding (they are linear operations and can be permuted), the necessary decoding operations in the preprocessor are reduced by 2 orders of magnitude. The master controller for the device is programed by a 1024 4-bit instruction PROM. There are 16 different instructions allowing the necessary flexibility for different code and sampling schemes. The transmitter and analog-to-digital converter are also controlled by the same device. Stratospheric and mesospheric echoes obtained with the help of this device are presented for illustration. The detection of layers as thin as 150 m or less at both stratospheric and mesospheric heights justified the efforts to achieve the maximum resolution possible."Item Open Access A cooperative synchronous observation of winds and tides in the tropical lower stratosphere and mesosphere using VHF radars at Jicamarca and Arecibo(Society of Geomagnetism and Earth, Planetary and Space Sciences, 1986-04) Maekawa, Yasuyuki; Aso, Takehiko; Róttger, Jürgen; Czechowsky, Peter; Rüster, Rüdiger; Schmidt, Gerhard; Hirota, Isamu; Woodman Pollitt, Ronald Francisco; Kato, SusumuA cooperative synchronous observation of winds in the tropical lower stratosphere and mesosphere was carried out using VHF radars at Jicamarca (11.95°S, 76.87°W) and at Arecibo (18.35°N, 66.75°W) on 19-21 or 23 November 1981. The comparison between observations about symmetrical north and south of the equator is focussed on the mean and tidal wind characteristics. Vertical structures of the mean zonal winds at both observational stations are in fairly good agreement with the CIRA (1972) zonal circulation model at the corresponding latitudes. The nature of lower stratospheric diurnal tides is similar between Jicamarca and Arecibo. Their vertical profiles generally correspond to the theoretical predictions based on the fundamental tidal modes. The vertical scale of the tidal components including higher-order modes is shown to be longer than 10km. In the mesosphere, vertically propagating diurnal tide which is expected to be predominant at lower latitudes is partially detected in daytime at Arecibo, while it is not so well-defined at Jicamarca, suggesting a variable nature of the relevant tidal modes.Item Open Access A digital-analogue match filter for piecewise square pulses(Instituto Geofísico del Perú, 1977-02-03) Woodman Pollitt, Ronald FranciscoIt is well known that the optimum signal to noise ratio in a radar is obtained when the receiver response is matched to the transmitter pulse shape. A matched receiver has an impulse response, g(t), equal to the negative fold of the transmitter pulse shape, p(t), i .c.: g(t) = p(-t). On the other hand we have that for a given maximum peak and average power the pulse length is shortest when the transmitter pulse has a square or piecewise square shape (sequences of positive and negative pulses. In many cases the square shapes are the easiest, if not the only possible, shapes that can be obtained in a transmitter. Here we use "square" to imply pulses with fairly constant amplitude and relative short transit times. Square-wave receiver input responses can not he Obtained with simple lumped element filters. One needs either taped delay lines or digital techniques. The present note describes a hybrid analog-digital technique to achieve a matched set of piecewise "square" transmitter pulse shapes and receiver input response. The scheme works also for phase (0-180°) coded pulse sequences. The scheme is a natural use for a digital decoder for phase coded pulses. First we shall describe the operation for n single square pulse. The extension to a phase coded sequence is straightforward.Item Open Access A double demodulation algorithm for narrow spectral features(Instituto Geofísico del Perú, 1995) Ragaini, Enrico; Woodman Pollitt, Ronald FranciscoThis paper proposes a technique for processing signals in which the relevant feature consists of the shape and position of narrow doppler spectral lines. The proposed technique is the digital version of a quadrature demodulator, and its purpose is to demodulate a selected spectral line allowing to study its envelope as a slowly varying process.Item Restricted A general statistical instrument theory of atmospheric and ionospheric radars(American Geophysical Union, 1991-01) Woodman Pollitt, Ronald FranciscoSome basic functional relationships between the statistics of the signals received in a radar and the statistics of the density fluctuations of a scattering medium are derived. They vary in their degree of generality, but they are all very general in scope. They include monostatic and bistatic radars scattering from either atmospheric, ionospheric, or meteorological media. They are valid for refractive and slightly dispersive media, so they can also be used for HF ionospheric radars. They include the effects of filtering, including receiver filtering, pulse compression coding and decoding schemes, and coherent integration, or any alternative linear digital filtering scheme. Functional relationships to include cross-correlation schemes, such as Faraday rotation experiments and interferometers, are included. Some simplified expressions are derived for frequently encountered situations, where different approximations can be made. These simplified expressions cover a large number of radar techniques currently in use for atmospheric and ionospheric applications.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-DSP signal processing and control system for MST radar(IEEE, Institute of Electrical and Electronics Engineers, 1995) Sarango, Martin F.; Woodman Pollitt, Ronald Francisco; Ragaini, Enrico; Vásquez, Edilberto H.This paper describes a signal processing and control system for atmospheric sounding rardars, with improved characteristics with respect to formerly used architectures. We refer especially to wind profiling as an important and interesting application. The system allows up to 4 receiver signals to be processed at the same time, with 60 range gates and 300 m height resolution. The use of two DSPs working in parallel allows the use of a single PC for real time data processing and system control. Some experimental results and reported.Item Open Access A Narrow-Band Tracking Filter(NASA, 1964-01-17) Woodman Pollitt, Ronald FranciscoThe characteristics of a servo phase-lock tracking filter is described herein. The filter tracks a 100 cps carrier with a bandwidth of either 0.3 cps or 0.03 cps. The advantages of this type filter and its use is also discussed.Item Open Access A new approach in incoherent scatter F region E x B drift measurements at Jicamarca(American Geophysical Union, 1999-12-01) Kudeki, E.; Bhattacharyya, S.; Woodman Pollitt, Ronald FranciscoSince 1996 incoherent scatter F region plasma drift measurements at Jicamarca have been implemented using a new signal processing approach replacing the traditional pulse-to-pulse correlation method. The new method, based on Doppler spectrum estimation and nonlinear least squares fitting to model spectra obtained from incoherent scatter theory, improves the instrumental sensitivity remarkably under low signal-to-noise conditions. With the new method it has become possible to obtain very high quality drifts data at nearly all hours of the day throughout most F region heights. Altitudinal smoothing of the drifts data to reduce measurement noise is no longer necessary, and studies of the height variations of drifts can be performed with much greater certainty than before. Small-amplitude gravity wave oscillations have been detected at F region heights and a vortical circulation of the F region plasma has been observed in the post sunset period.Item Open Access A new phase measuring technique for the minitrack satellite tracking system(Instituto Geofísico del Perú, 1960) Woodman Pollitt, Ronald FranciscoA New Phase Measuring Technique has been developed as a solution to some of the present limitation of Minitrack Satellite Tracking System. Two main problems are solved, one concerned with the processing of the information and the other, with the sensitivity of the system. The present Minitrack is not a real time system. The output information has to be solved from ambiguity, smoothed, and corrected at a centralized computer location with a resultant time delay. The output of the mew system is real time, free from ambiguity, and fully corrected. It will be used to plot the satellite position in X and Y coordinates and could be used to drive telemetry, antennas or optical cameras. Its digital output is a five decimal digit directional cosine number ready for transmission to the centralized computer for orbital computation. The present Minitrack sensitivity is determined by a passive 10 cps bandwidth filter. The bandwidth is the narrowest bandwidth with linear phase vs frequency characteristics for a maximun differential doppler shift of 2 cps (approximately 2 ° per second angular rate).Item Open Access A phase-locked phase filter for the minitrack system(National Aeronautics and Space Administration, 1962-09) Woodman Pollitt, Ronald FranciscoA variable-bandwidth filter has been designed and built to narrow the postdetection bandwidth of the Minitrack satellite tracking system. It is based on phase-lock techniques. Al its narrowest bandwidth, 0.03 cps, the phase peak-topeak noise deviations are reduced to ± 1.5 percent of a wavelength for a signal strength of -140 dbm coming into the receiver "front ends". The filter introduces no phase shift or time delay regardless of the signal phase rate.Item Restricted A poststatistics steering technique for MST radar applications(American Geophysical Union, 1990-07) Kudeki, Erhan; Woodman Pollitt, Ronald FranciscoA new interferometric data analysis procedure equivalent to software beam synthesis and scanning is introduced. It is shown that the self- and cross-spectra of interferometric multiple-receiver signals can be linearly combined to obtain the self- and cross-spectra of radar returns from selected viewing directions within the two-way radar beam pattern.Item Open Access A progress report on scintillation observations at Ancón And Jicamarca observatories(Goddard Space Flight Center, GSFC, 1970-10) Pomalaza, José; Woodman Pollitt, Ronald Francisco; Tisnado, Gilberto; Sandoval, Jaime; Guillén, AlbertoThe purpose of this report is to present a preliminary analysis of the data collected in connection with NASA contract work with ESSA (ESSA contract No. E22-9-70(N)). Under this contract a study of equatorial ionospheric irregularities using satellite transmissions is being performed.Item Open Access A proposed VHF radar experiment in relation to stratospheric pollution problems(Instituto Geofísico del Perú, 1976-06-01) Woodman Pollitt, Ronald FranciscoThere is no need to stress here the importance of current stratospheric research motivated by possible man-made disturbances of the natural chemical equilibrium state of ozone in the stratosphere. The subject is discussed not only in the technical literature but in newspapers, magazines and television programs. This includes the effects of high flying aircraft, fluor carbon releases from aerosol cans and airconditioning units and more recently the effects of enhanced soil production of N20 as a consequence of the use of artificial fertilizers.Item Open Access A San Marco/Jicamarca study of equatorial spread F(Instituto Geofísico del Perú, 1987) Kelley, M.C.; Woodman Pollitt, Ronald FranciscoOver the years at number of experimental technique have been employed to understand equatorial spread F (ESF). The field is by now very advanced as is our understanding of the relationship between the Jicamarca Radar Maps and in situ measurements .This is important since the ground based data is less expensive to obtain and is available over seasonal and even solar cycle time basis.The advanced understanding has come primarily from rocket/radar, satellite/radar and theoretical studies.Item Open Access Algunos apuntes históricos adicionales sobre la cronología de El Niño(Instituto Frances de Estudios Andinos, 1993) Mabres, Antonio; Woodman Pollitt, Ronald Francisco; Zeta, RosaEs necesario continuar haciendo esfuerzos para establecer un registro homogéneo y lo más completo y confiable posible de los eventos del fenómeno ENSO. La región de Piura tiene una alta sensibilidad al fenómeno, cuya presencia da lugar siempre a las abundantes lluvias. Por esto, las fuentes históricas provenientes de esta región son muy importantes. Además complementarán los estudios dendrocronólogicos que se realizan también en la región. Se dan nuevas fuentes históricas sobre las lluvias en Piura. La más interesante es del periódico "El Amigo del Pueblo", del año 1906, que recoge datos a año de 1791 a 1906. Se observa una notable concordancia con la cronología de Eguiguren que recogió Woodman (1985) y que se amplía con dichas fuentes. En cambio, hay algunas discrepancias con la relación de eventos fuertes y medianos que dan Quinn et al. (1987). Se señalan algunos de los intervalos de años (y en años singulares) extremadamente secos en los últimos 200 años.Item Open Access An analysis technique for deriving vector winds and in-beam incidence angles from radar interferometer measurements(American Meteorological Society, 1992-02) Larsen, M. F.; Palmer, R. D.; Fukao, S.; Woodman Pollitt, Ronald Francisco; Yamamoto, M; Tsuda, T; Kato, S.We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.Item Open Access An autocorrelation scheme using a complex approach (phase detectors) with N multiplier-accumulators for N frecuency points(Editor no identificado, 1981-07-08) Woodman Pollitt, Ronald FranciscoThe purpose of this note is to present a scheme which permits implementation of both systems, therefore, allowing one to trade bandwidth for frequency resolution, but using only one frequency conversion scheme, for both: the simpler complex conversion (phase detection) scheme. It involves only the introduction of a time multiplexer between the complex digitized signals and a real correlator.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.