Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Over 100 tons of material enters the Earth's atmosphere every day, mostly in the form of meteoroids less than a millimeter across. As a meteoroid enters the atmosphere, it ablates and forms a plasma. Radars can detect this plasma, which travels at approximately the same speed as the meteoroid, as a head echo. Such observations can determine the speed and trajectory of a meteoroid with high accuracy. A better characterization of these small particles will contribute to our understanding of the Earth's atmosphere, the solar system, and the local interstellar medium. Meteoroids provide a source of heavy metals at high altitudes that impact atmospheric chemistry and physics. Greater knowledge of the composition and masses of meteoroids will help astronomers understand the material within the solar system and the local interstellar medium. This dissertation focuses on meteoroid head echo observations using the 50 MHz radar at the Jicamarca Radio Observatory. These provide high resolution observations in both range and time. We use this data to evaluate methods of determining meteoroid properties and introduce a technique to determine meteoroid mass which involves fitting range and velocity measurements to an ablation model. This technique is compared with some established mass estimation methods, including scattering mass theory. We find the overall mass distribution for observed meteoroids as well as the spatial distribution of these particles. The peak of our mass distribution, at approximately 10^-11 kg, is significantly lower than what is found using specular meteor radars. We illustrate how the spatial distribution varies with meteoroid mass, and how different meteoroid sources appear when different mass ranges are examined. For the smallest meteoroids, only the Apex sources are detected, while all six of the dominant meteor sources are observed with comparable intensity when examining meteors with a mass larger than 10^-9 kg. We also directly compare meteor data taken with the 50 MHz radar to observations using a specular meteor radar in a novel experiment using both instruments simultaneously. / 2031-01-02

En el Radio Observatorio de Jicamarca(ROJ) se ha desarrollado un sistema receptor digital de señales de radiofrecuencia provenientes de satélites de baja orbita. Este receptor terrestre calcula la variación del Contenido Total de Electrones(rTEC, del ingles relative Total Electron Content) en la ionosfera que tal y como su nombre lo diceel rTEC esta relacionado al contenido total de electrones o densidad de iones en la ionosfera. Este sistema tiene la capacidad de obtener señales transmitidas desde nano satélites y satélites en general que cuenten con un payload especifico. En un futuro el sistema receptor será capaz de captar las señales del transmisor del nanosatélite desarrollado por el ROJ. Las mediciones del rTEC obtenidas permitirán investigar la ionósfera ecuatorial y observar eventos y fenomenos de interés cuando se presenten irregularidades. En el presente trabajo de tesis, se hará una descripción del sistema y se explicará cómo el sistema receptor determina el rTEC usando la técnica llamada Differential Doppler. Así mismo se mostrarán los resultados de detección del rTEC utilizando las señales de radio frecuencias transmitidas por satélites que se encuentran operativos como COSMOS, CASSIOPE y DMSP-F15. Finalmente se mostraran las comparaciones de estos resultados con mediciones obtenidas por otro receptor del tipo analógico, las cuales presentan un alto índice de correlación. / A radio beacon receiver system is being developed at the Jicamarca Radio Observatory. This ground-based receiver will be used to obtain ionospheric total electron content (TEC) over the Peruvian region by detecting satellite radio beacon signals. This work is part of a project that involves the development of a CubeSat radio beacon for ionospheric measurements. The receiver station will have the capability to obtain differential phase measurements from current operational satellite radio beacons and from the new CubeSat radio beacon developed at the Jicamarca Radio Observatory. Due to the proximity to the magnetic equator, the obtained TEC measurements will allow the investigation of the equatorial ionosphere which plays a significant role in the generation of irregularities such as the equatorial spread F. Here, we present a description of the initial beacon receiver system design which is based on quadrifilar helix antennas, cavity filters, amplifiers and software-defined radio equipment. Initial simulations and tests of the different stages of the receiver system, including the algorithm for the data acquisition, will be shown. In addition, we will describe the design and tests of our cavity filters that show a better performance than commercial ones. Finally, we will explain how the receiver system determinates the TEC in the ionosphere using the Differential Doppler technique and how multi-ples scientific satellites constellations like COSMOS and COSMIC help us to do our measurements. This receiver system instrumentation will add to the set of groundbased instruments already operating at the Jicamarca Radio Observatory and will provide a valuable data set for ionospheric research. / Tesis