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This thesis explores one possible method of preventing helicopter crashes caused by brownout using the noise generated by the helicopter rotor as an altimeter. The hypothesis under consideration is that the helicopter's height, velocity, and obstacle locations with respect to the helicopter, can be determined by comparing incident and reflected rotor noise signals, provided adequate bandwidth and signal to noise ratio. Heights can be determined by measuring the cepstrum of the reflected helicopter noise. The velocity can be determined by measuring small amounts of Doppler distortion using the Mellin-Scale Transform. Height and velocity detection algorithms are developed, optimized for this application, and tested using a microphone array. The algorithms and array are tested using a hemianechoic chamber and outside in Georgia Tech's Burger Bowl. Height and obstacle detection are determined to be feasible with the existing array. Velocity detection and surface mapping are not successfully accomplished.

Táto diplomová práca sa zaoberá návrhom a implementáciou algoritmu pre spracovaniu signálu z radaru využívajúceho frekvenčne modulovanú kontinuálnu vlnu. Cieľom je implementácia algoritmu, ktorý by bol dostatočne rýchly (výpočet v reálnom čase na cieľovej platforme) a dostatočne presný pre použitie v rádiovýškomere v ľahkom lietadle so zameraním na použitie počas pristávacieho manévru. Hlavnou metódou spracovania signálu, použitou v implementácii, je Diskrétna Fourierova transformácia. Vytvorený algoritmus bol otestovaný na reálnych letových dátach a pre pristávací manéver dosiahol uspokojivé výsledky.

Approved for public release, distribution is unlimited / The purpose of this thesis is to determine the effect that the inclusion of satellite altimeter data has on weapon preset accuracy. GDEM data and MODAS data utilizing four satellite altimeters were used by the Weapon Acoustic Preset Program to determine the suggested presets for a Mk 48 torpedo. The acoustic coverage area generated by the program will be used as the metric to compare the two sets of outputs. The assumption is that the MODAS initialized presets will be more accurate, and, therefore, the difference between the two sets of presets can be attributed to inaccuracy on the part of the GDEM presets. Output presets were created for two different scenarios, an Anti-Surface Warfare (ASUW) scenario and an Anti-Submarine Warfare (ASW) scenario, and three different depth bands, shallow, mid, and deep. After analyzing the output, it became clear that the GDEM data predicted a weapon effectiveness that was far higher than the effectiveness predicted by the MODAS data. Also, while GDEM predicted a wide range of coverage percentages MODAS predicted a narrow range of coverage percentages. / Ensign, United States Navy

A resposta oceânica a perturbações com períodos e comprimentos significativamente maiores que o período inercial e que o raio de deformação de Rossby se dá na forma de ondas de Rossby planetárias. Geralmente, as perturbações são atribuídas a variações no rotacional do vento via bombeamento de Ekman. A passagem dessas ondas causa deformação das isopicnais, podendo resultar em anomalias da temperatura da superfície do mar (TSM) por advecção vertical. Dependendo de como ocorre a interação ar-mar, anomalias de TSM podem alterar o campo de ventos ou serem alteradas por ele através de fluxo de calor. Este trabalho utiliza dez anos de dados de temperatura da superfície do mar, velocidade e direção dos ventos e anomalia da altura do mar obtidos por satélites para identificar regiões do oceano onde há forçamento direto do vento na geração de ondas planetárias que se propagam linearmente. Mapas de correlação cruzada entre essas variáveis permitiram identificar onde a interação entre o oceano e a atmosfera é linear. Um modelo simples de uma camada e meia forçado apenas pelo bombeamento de Ekman foi utilizado para testar se, nestas regiões, a variabilidade atmosférica seria suficiente para explicar a variabilidade das ondas de Rossby estimadas pelos dados altimétricos. A interação entre a TSM e a intensidade do vento no Atlântico sul tropical é distinta das demais bacias oceânicas. Das correlações entre a TSM e o rotacional da tensão de cisalhamento do vento, observou-se que a dinâmica de Ekman não é marcante no Índico. Nas regiões tropicais do Atlântico e do Pacífico, as previsões do modelo foram similares às observações. Por fim, foram obtidas evidências de geração e retroalimentação de ondas planetárias nas bordas leste do Atlântico e do Pacífico. / Rossby waves are the ocean response to perturbations whose temporal and spatial scales are significantly longer than both the inertial period and the Rossby radius of deformation. These perturbations are, more often than not, attributed to variations in the wind stress curl {\\em via} Ekman pumping. The waves cause isopycnal displacement which due to vertical advection may result in sea surface temperature (SST) anomalies. Depending on the ocean--atmosphere interaction, SST anomalies can either change the wind field or be changed by it due to the heat flux. This study makes use of ten years of satellite derived SST, wind vector, and sea surface height anomaly data to identify regions where there is direct wind forcing of linear Rossby waves. Cross-correlation maps between these variables show where linear interactions occur. A simple 1½ layer model forced by Ekman pumping was used to check if, in those regions, atmospheric variability alone can explain the observed Rossby wave variability as estimated from radar altimeter data. The interaction between SST and wind magnitude in the South Atlantic is distinct from all other ocean basins. SST and wind stress curl correlations show that the Ekman dynamics is not dominant in the Indian Ocean. In the tropical Atlantic and Pacific the model predictions are similar to the observations. Finally, evidence of genesis and feedback of planetary waves is presented for the eastern boundaries of the Atlantic and Pacific oceans.

A resposta oceânica a perturbações com períodos e comprimentos significativamente maiores que o período inercial e que o raio de deformação de Rossby se dá na forma de ondas de Rossby planetárias. Geralmente, as perturbações são atribuídas a variações no rotacional do vento via bombeamento de Ekman. A passagem dessas ondas causa deformação das isopicnais, podendo resultar em anomalias da temperatura da superfície do mar (TSM) por advecção vertical. Dependendo de como ocorre a interação ar-mar, anomalias de TSM podem alterar o campo de ventos ou serem alteradas por ele através de fluxo de calor. Este trabalho utiliza dez anos de dados de temperatura da superfície do mar, velocidade e direção dos ventos e anomalia da altura do mar obtidos por satélites para identificar regiões do oceano onde há forçamento direto do vento na geração de ondas planetárias que se propagam linearmente. Mapas de correlação cruzada entre essas variáveis permitiram identificar onde a interação entre o oceano e a atmosfera é linear. Um modelo simples de uma camada e meia forçado apenas pelo bombeamento de Ekman foi utilizado para testar se, nestas regiões, a variabilidade atmosférica seria suficiente para explicar a variabilidade das ondas de Rossby estimadas pelos dados altimétricos. A interação entre a TSM e a intensidade do vento no Atlântico sul tropical é distinta das demais bacias oceânicas. Das correlações entre a TSM e o rotacional da tensão de cisalhamento do vento, observou-se que a dinâmica de Ekman não é marcante no Índico. Nas regiões tropicais do Atlântico e do Pacífico, as previsões do modelo foram similares às observações. Por fim, foram obtidas evidências de geração e retroalimentação de ondas planetárias nas bordas leste do Atlântico e do Pacífico. / Rossby waves are the ocean response to perturbations whose temporal and spatial scales are significantly longer than both the inertial period and the Rossby radius of deformation. These perturbations are, more often than not, attributed to variations in the wind stress curl {\\em via} Ekman pumping. The waves cause isopycnal displacement which due to vertical advection may result in sea surface temperature (SST) anomalies. Depending on the ocean--atmosphere interaction, SST anomalies can either change the wind field or be changed by it due to the heat flux. This study makes use of ten years of satellite derived SST, wind vector, and sea surface height anomaly data to identify regions where there is direct wind forcing of linear Rossby waves. Cross-correlation maps between these variables show where linear interactions occur. A simple 1½ layer model forced by Ekman pumping was used to check if, in those regions, atmospheric variability alone can explain the observed Rossby wave variability as estimated from radar altimeter data. The interaction between SST and wind magnitude in the South Atlantic is distinct from all other ocean basins. SST and wind stress curl correlations show that the Ekman dynamics is not dominant in the Indian Ocean. In the tropical Atlantic and Pacific the model predictions are similar to the observations. Finally, evidence of genesis and feedback of planetary waves is presented for the eastern boundaries of the Atlantic and Pacific oceans.

Dans le contexte actuel du réchauffement climatique, l'une des principales sources d'incertitude pour l'élévation du niveau de la mer est la contribution de la calotte Antarctique. L'étendue et les conditions météorologiques extrêmes de ce continent font de la télédétection spatiale un moyen utile pour son suivi sur le long terme. Les observations satellites altimétriques et radiométriques dans la gamme des micro-ondes rendent compte de l'évolution des propriétés du manteau neigeux de la calotte. L'altimétrie radar, par des mesures répétées de l'élévation de la topographie de surface, permet de quantifier les variations de volume sur l'ensemble du continent. Cependant, la pénétration de l'onde radar dans la neige affecte négativement cette quantification. Les méthodes proposées pour minimiser les erreurs de pénétration sont toutes basées sur des relations avec le coefficient de rétrodiffusion radar. La compréhension des variations annuelles et inter-annuelles du coefficient de rétrodiffusion est nécessaire pour améliorer la précision de l'estimation de l'élévation de la surface donc du bilan de volume de la calotte. Cette thèse a pour objectif d'étudier le coefficient de rétrodiffusion mesuré par les altimètres sur l'ensemble du continent, sujet qui jusqu'à aujourd'hui a reçu peu d'attention. Les altimètres radars embarqués à bord d'ENVISAT (bandes S et Ku) et de SARAL/AltiKa (bande Ka) ont des sensibilités différentes aux propriétés de la neige. Nous nous sommes intéressés aux caractéristiques annuelles et inter-annuelles des coefficients de rétrodiffusion dans ces trois bandes. Une étude de sensibilité a été réalisée avec un modèle électromagnétique afin de déterminer les propriétés du manteau neigeux qui dominent le signal saisonnier. On montre que le signal saisonnier est sensible à la densité et la rugosité de surface dans la bande S, à la température de la neige dans la bande Ka et à l'une ou à l'autre de ces variables selon la région dans la bande Ku. Les caractéristiques saisonnières du coefficient de rétrodiffusion sont ensuite comparées à celles des températures de brillance acquises par les radiomètres à bord de SARAL et de SSM/I. Les résultats indiquent une influence significative de la rugosité de surface sur les températures de brillance de la bande Ka, influence souvent considérée négligeable dans la modélisation de la température de brillance. Cette étude apporte une meilleure connaissance de la dynamique saisonnière des propriétés de proche surface de la calotte Antarctique. Elle fournit de nouveaux indices pour développer dans le futur des algorithmes robustes de correction de l'erreur de pénétration. Elle met également en lumière l'importance des missions altimétriques multi-fréquences et les possibilités qu'offrent le signal de la bande S pour l'étude des variabilités saisonnières de la rugosité de surface. En définitive, la rugosité de surface est un paramètre important à prendre en compte pour obtenir de meilleures estimations et modélisations des coefficients de rétrodiffusion et des températures de brillance. / In the context of global climate changes, the Antarctic ice sheet contribution to sea-level rise is one of the main uncertainty sources. The extent and extreme meteorological conditions of this continent render remote sensing a useful tool for long term monitoring. Altimetry and radiometry observations in the microwave range reveal variations of the volume of the ice sheet and surface properties of the snowpack. Radar altimeters, provide repeated observations of the surface topography elevation, which allow the quantification of volume variations of the ice sheet. However, the penetration of radar waves in dry and cold snowpack adversely affects the estimated surface elevation. Approaches to minimize the penetration error are all based on a relationship with the backscattering coefficient. Understanding the annual and interannual variations of the backscattering coefficient is thus a key issue in order to improve the estimation accuracy of the surface elevation and to refine the ice-sheet volume trend. This thesis aims at studying the backscattering coefficients acquired by radar altimeters, which until now have received little attention. Radar altimeters on board ENVISAT (S and Ku bands) and SARAL/AltiKa (Ka band) have different sensitivities to the snowpack properties. The annual and interannual variations of the backscattering coefficient at the three bands is investigated. Sensitivity tests are carried out with an electromagnetic model to determine the prevailing snowpack properties that drive the signal. The seasonal signal is sensitive to surface density and roughness at S band, to snow temperature at Ka band and to either snow surface density and roughness or temperature depending on the location on the continent at Ku band. The seasonal signal of the backscattering coefficient is then compared with that of the brightness temperature measured by radiometers on SARAL and SSM/I. The results show a significant influence of surface roughness on brightness temperatures at Ka band, which has often been neglected in brightness temperature modeling studies. This thesis provides a better understanding of the seasonal dynamics of the near surface properties of the Antarctic ice sheet. It also provides new clues to build a more robust corrections of the penetration errors in the future. It highlights the importance of multi-frequency altimetry missions and the potential of the S band to study the seasonal variability in surface roughness. In summary, surface roughness is an important property which should be taken into account for a better modeling of backscattering coefficient and brightness temperature.

This master's thesis deals with design and development of a system for measuring altitude (height above ground level) of flying objects. It describes theoretical background related to altitude measurements in avionics as well as various techniques of altitude measuring. The measurement is conducted by HMD (Height measuring device) - embedded system which uses barometric pressure sensor to measure altitude. The main part of this thesis is dedicated to ground unit - a server running custom set of applications. Using this server and radio link, it is possible to send control commands to HMD, receive data, and propagate data into web application. Furthermore server acts as a data storage and is able to process and analyse data. The thesis also discusses the precision of the measurement and the data output. System was tested and used during several glider aerobatics competitions.

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Este trabalho avalia a importância relativa dosmodos dinâmicos na composição da estrutura vertical do fluxo geostrófico e de suas anomalias em relação à média, com o objetivo de fornecer uma descrição das formas de estratificação predominantes na coluna de água e de identificar prováveis regiões de ocorrência de ondas de Rossby planetárias (OR) dos diversos modos dinâmicos. Raios de deformação internos são estimados para avaliar a possibilidade de interações não-lineares entre OR e as alterações da estratificação local forçadas por sua própria passagem. A análise proposta baseia-se em dados de densidade estimados a partir de perfis verticais de salinidade climatológicos aliados a perfis sintéticos de temperatura. Estes últimos são extrapolados verticalmente a partir de dados orbitais da temperatura da superfície do mar (TSM) e da anomalia da altura da superfície livre (h), segundo um método de reconstrução estatística desenvolvido para este estudo. O primeiro modo baroclínico é dominante tanto no fluxo total quanto em suas anomalias, respondendo em média por 30% da estrutura vertical de velocidade, sendo que este valor descresce aproximadamente por uma razão de três em modos superiores. O segundo modo é significativo ou mesmo dominante em algumas regiões, particularmente em latitudes próximas ao equador. O terceiro é evidente em algumas áreas localizadas, mas não assume papéis importantes em escala de bacia. O modo 0 responde por frações de 6 a 9%, mas é provável que estes resultados sejam subestimados pela metodologia aplicada. Anomalias verticais relacionadas ao primeiro modo coincidem com regiões onde OR longas do primeiro modo tem maior expressão, enquanto o segundo modo parece ser um marcador de OR curtas e ondas de instabilidade tropical. Fenômenos transientes associados ao terceiro modo são observados em áreas restritas dos três oceanos. A magnitude das variações dos raios internos em resposta à fenômenos transientes em algumas regiões implicam em variações significativas na velocidade de fase teórica de OR longas lineares, um indício de que efeitos não-lineares podem ser importantes. Por fim, amplificações da importância do modo barotrópico sobre feições topográficas significativas sugere a existência de mecanismos de transferência de energia entre modos dinâmicos induzidas pela interação com a batimetria. / This study evaluates the relative importance of the dynamical modes in the composition of the geostrophic flow and of its anomalies from the long-term average, respectively seeking to determine the dominant vertical stratification structures of the water column and to identify regions where planetary Rossby waves (RW) of different dynamical modes may most likely occur. The baroclinic Rossby radii of deformation are estimated to evaluate the possibility of nonlinear interactions between RWand changes of the local stratification forced by the wave\'s passing. This analysis is based on density data estimated from climatological salinity profiles and synthetic temperature profiles. The latter are vertically extrapolated for sea surface temperature (SST) and sea surface height anomaly (h) satellite data, using a statistical reconstruction method developed in this study. The first baroclinic mode dominates both the total geostrophic flow and its anomalies, accounting for 30% of the velocity\'s vertical structure on average, where this value decreases approximately by a factor of 3 in subsequent baroclinic orders. The second mode is significant or even dominant in some areas, particularly near the equator. The third mode is evident in some localized regions, but can be ignored at basin-scales. The barotropic mode accounts for 6 to 9% fractions on average, however these values are probably underestimated by the used methods. Vertical anomalies related to the first baroclinic mode coincide with regions where long RWs answers for a significant fraction of local variance, while the second mode highlights zones where short RWs and tropical instability waves are reported. Transient phenomena related with the third mode are observed in comparatively small areas on all three oceans. The magnitude of the baroclinic radii\'s variations in response of the transient variability results in significant changes of the theorethical phase speed for long linear RWs, an evidence that nonlinear effects may be important. Lastly, the greater significance of the barotropic mode over proeminent bottom features suggests the existence of energy transfer mechanisms between dynamical modes triggered by the interaction with the bathymetry.