Neural networks and early fast Doppler for prediction in meteor-burst communications systems.

Thesis (Ph.D.)-University of Natal, Durban, 1994.In meteor-burst communications systems, the channel is bursty with a continuously fluctuating signal-to-noise ratio. Adaptive data rate systems attempt to use the channel more optimally by varying the bit rate. Current adaptive rate systems use a method of closed-loop decision-feedback to control the transmitted data rate. It is proposed that an open-loop adaptive data rate system without a decision feedback path may be possible using implicit channel information carried in the first few milliseconds of the link establishment probe signal. The system would have primary application in low-cost half-duplex telemetry systems. It is shown that the key elements in such a system would be channel predictors. The development of these predictors is the focus of this research. Two novel methods of predicting channel parameters are developed. The first utilises early fast Doppler information that precedes many long duration, large signal-to-noise-ratio overdense trails. The presence of early fast Doppler at the trail commencement is used as a toggle to operate at a higher data rate. Factors influencing the use of early fast Doppler for this purpose are also presented. The second method uses artificial neural networks. Data measured during trail formation is processed and presented to the neural networks for prediction of trail parameters. Several successful neural networks are presented which predict trail type, underdense or overdense, and peak trail amplitude from the first 50ms of the trail's lifetime. This method allows better estimation of the developing trail. This fact can be used to implement a multi-rate open-loop adaptive data rate system

Simple meteor scatter out-station antennas

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, infulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1989T his dissertation examines simple Meteor Burst Communication (M B C) out-starioL * i-^nas. The eSect o f illum ination gain, beam w idth and orientation was studied using computer ^vr.t-iation. Sim ilarly, the performance o f M B C links using a half-wave dipole, a quarter-wave rnonopole, a square loop, a long w ue and a 5-elements Yagi-Uda antennas was determined. The performance o f these links are related to the antennas’ sky i l l umination. This investigation provides designers some bench-mark results which indicate the role played by the antennas ’ radiation patterns in M B C. A value system was formulated to provide practical and electrical trade-offs fo r m obile andmanpack antennas in the meteor scatter environment. Simulated results indicate that simple antennas cause degraded communications due to their reduced size and complexity. The conclusion is that the directional master station should provide adequate sky illumination. I t is recommended that the results obtained be validated by measurements and further work concentrate on master station antennas

Characterisation of the Perseid meteoroid stream through SPOSH observations between 2010–2016

We have characterised the Perseid meteoroid stream from data acquired in a series of observing campaigns between 2010 and 2016. The data presented in this work were obtained by the Smart Panoramic Optical Sensor Head (SPOSH), an all-sky camera system designed to image faint transient noctilucent phenomena on dark planetary hemispheres. For the data reduction, a sophisticated software package was developed that utilises the high geometric and photometric quality of images obtained by the camera system. We identify 934 meteors as Perseids, observed over a long period between late July (~124°) and mid-to-late August (~147°). The maximum meteor activity contributing to the annual shower was found at λ⊙ = 140°.08 ± 0°.07. The radiant of the shower was estimated at RA = 47°.2 and Dec = 57°.5 with a median error of 0°.6 and 0°.2, respectively. The mean population index of the shower between solar longitudes of 120°.68 and 145°.19 was r = 2.36 ± 0.05, showing strong temporal variation. A predicted outburst in shower activity for the night of August 11–12, 2016 was confirmed, with a peak observed 12.75 hr before the annual maximum at 23:30 ± 15′ UT. We measure a peak flux of 6.1 × 10−4 km−2 hr−1 for meteoroids of mass 1.6 × 10−2 g or more, appearing in the time period between 23:00 and 00:00 UT. We estimate the measured flux of the outburst meteoroids to be approximately twice as high as the annual meteoroid flux of the same mass. The population index of r = 2.19 ± 0.08, computed from the outburst Perseids in 2016, is higher than the value of r = 1.92 ± 0.06 derived from meteors observed in 2015 belonging to the annual Perseid shower which was active near the time of the outburst. A dust trail with an unusually high population index of r = 3.58 ± 0.24 was encountered in 2013 between solar longitudes 136°.261 and 137°.442. The relatively high r-value implies an encounter with a dust trail rich in low-mass particles

Explosive Transient Camera (ETC) Program

Since the inception of the ETC program, a wide range of new technologies was developed to support this astronomical instrument. The prototype unit was installed at ETC Site 1. The first partially automated observations were made and some major renovations were later added to the ETC hardware. The ETC was outfitted with new thermoelectrically-cooled CCD cameras and a sophisticated vacuum manifold, which, together, made the ETC a much more reliable unit than the prototype. The ETC instrumentation and building were placed under full computer control, allowing the ETC to operate as an automated, autonomous instrument with virtually no human intervention necessary. The first fully-automated operation of the ETC was performed, during which the ETC monitored the error region of the repeating soft gamma-ray burster SGR 1806-21

Single- and dual-carrier microwave noise abatement in the deep space network

The NASA/JPL Deep Space Network (DSN) microwave ground antenna systems are presented which simultaneously uplink very high power S-band signals while receiving very low level S- and X-band downlinks. Tertiary mechanisms associated with elements give rise to self-interference in the forms of broadband noise burst and coherent intermodulation products. A long-term program to reduce or eliminate both forms of interference is described in detail. Two DSN antennas were subjected to extensive interference testing and practical cleanup program; the initial performance, modification details, and final performance achieved at several planned stages are discussed. Test equipment and field procedures found useful in locating interference sources are discussed. Practices deemed necessary for interference-free operations in the DSN are described. Much of the specific information given is expected to be easily generalized for application in a variety of similar installations. Recommendations for future investigations and individual element design are given

Técnicas de detección y caracterización de la materia interplanetaria próxima a la Tierra desde observatorios en tierra

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Astrofísica y Ciencias de la Atmósfera, leída el 05/06/2017Interplanetary matter covers a wide range of mass and size in the Universe, from micrometric dust to multi-kilometre asteroids. This matter plays countless roles in planetary sciences. Dust fills the space in the Solar System, but also in a myriad of exoplanetary systems. Indeed, the interplanetary dust usually outshines the planets in infrared and these hot debris disks have already been observed in several exoplanetary systems. The near-Earth interplanetary matter is also relevant for Earth sciences and space exploration. Extraterrestrial dust plays several roles in the upper atmosphere. Moreover the asteroids are a threat for humankind due to the energy they release in the case of impact against the planet. Asteroids larger than 1 km could produce global devastation and 90% of them are already catalogued. Current efforts are focused on the population larger than 140 m, able to produce an impact of regional proportions. Beyond Earth’s atmosphere, these bodies pose a hazard to spacecraft, especially the small particles that are the most numerous but still carry enough energy to jeopardise their systems. This dissertation undertakes the research of the interplanetary matter near the Earth using two different observational approaches. The first one is based on the detection of the sunlight reflected by the bodies. Individuals bodies can be observed with the use of telescopes, they are the asteroids. For objects close to the Earth the accessible range in size is wider, down to the decametre size and consequently this population are a probe to general population of asteroids in the Solar System. Especially if we consider that recent works suggest that objects larger and smaller than 200 m could be two different populations, being the smaller monolithic bodies while larger ones are more likely rubble piles. And we only have access to the smaller population if they come close enough to the be observable. The detection and characterisation of these nearby population require networks of medium-sized telescopes to survey and track them. We design a robotic system (the TBT telescopes) for the European Space Agency as a prototype for a future network. The first unit is already installed in Spain and we present the results of the commissioning. Additionally we evaluate the expected performance of such an instrument using a simulation with a synthetic population. We consider that the system designed is a powerful instrument for nearby asteroid discovery and tracking. It is based on commercial components, and therefore ready for a scalable implementation in a global network...Bajo el término de materia interplanetaria se engloban objetos en un gran rango de masas y tamaños en el Universo, desde el polvo micrométrico hasta los asteroides de centenares de kilómetros de diámetro. Esta materia toma parte de innumerables procesos en las ciencias planetarias. Además el polvo no sólo está presente en el espacio del Sistema Solar, sino también en una infinidad de sistemas extrasolares. Más aún, el polvo interplanetario es más brillante en el infrarrojo que los propios planetas y ya se han observado muchos de estos discos circunestelares de polvo caliente. La materia interplanetaria en las cercanías de nuestro planeta es también relevante para el estudio de las ciencias de la Tierra y en la exploración espacial. El polvo extraterrestre participa en muchos procesos que tienen lugar en las capas más altas de la atmósfera. Asimismo los asteroides son una amenaza para la humanidad debido a la energía que pueden liberar en caso de impacto contra la Tierra. Se considera que los asteroides mayores de 1 km podrían provocar una catástrofe de proporciones globales y por ello el 90% de ellos ya han sido identificados. Actualmente los esfuerzos se centran en los objetos mayores de 140 m, con consecuencias sólo a nivel regional en caso de colisión. Fuera de la atmósfera terrestre estos cuerpos suponen un peligro para las naves espaciales, especialmente las partículas pequeñas que son las más numerosas y que pese a ello transportan energía suficiente como para comprometer su funcionamiento. Esta tesis estudia la materia interplanetaria desde dos aproximaciones observacionales distintas. Por un lado se observa la luz solar reflejada por estos cuerpos. En este caso encontramos a los asteroides, cuerpos que se pueden observar con telescopios hasta cierto tamaño. Para la población de objetos próximos a la Tierra el rango de tamaños que podemos observar es mayor, hasta tamaños de apenas decenas de metros. Por ello esta población se considera como una muestra relevante a la hora de estudiar la población general de asteroides en el Sistema Solar. Especialmente cuando estudios recientes afirman que puede haber una diferencia estructural entre las poblaciones con diámetro mayor y menor a unos 200 m, donde los pequeños son objetos monolíticos mientras que los grandes son agregados de objetos. Los objetos menores sólo son accesibles a los instrumentos si se aproximan lo suficiente a la Tierra. La detección y caracterización de estos objetos próximos requieren redes de telescopios de tamaño moderado. En este trabajo presentamos el diseño de un sistema robótico (los telescopios TBT) para la Agencia Espacial Europea (ESA), como prototipos de una red futura. El primero de ellos se encuentra ya instalado en España y se incluyen los resultados del comisionado. Por otro lado hemos analizado el rendimiento que se espera de ellos con ayuda de una simulación de las observaciones de una población sintética de objetos. Consideramos que el sistema diseñado es una herramienta potente para el descubrimiento y seguimiento de estos objetos próximos a la Tierra. Es un sistema basado en componentes comerciales y que por tanto se puede replicar para desarrollar una red global...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

Evolutionary and Physical Properties of Meteoroids

Astrophysical models for meteoroid formation and stellar and planetary evolutions are developed from simulation composition studies

Meteoroids: The Smallest Solar System Bodies

This volume is a compilation of articles reflecting the current state of knowledge on the physics, chemistry, astronomy, and aeronomy of small bodies in the solar system. The articles included here represent the most recent results in meteor, meteoroid, and related research fields and were presented May 24-28, 2010, in Breckenridge, Colorado, USA at Meteoroids 2010: An International Conference on Minor Bodies in the Solar System

NBS monograph

From Preface: "The purpose of this book is to replace, in part, a previous publication of the National Bureau of Standards (Circular 462) with the same title. The scope of the present work has therefore been broadened to include aspects of ionospheric radio propagation which were not treated in earlier publication.