Typescript. Bibliography: p. 199-208.

Le cadre de ces recherches est celui des radars bistatiques. Leurs avantages sont nombreux. Citons notamment, dans le domaine opérationnel : * exploitation potentielle de cibles de faibles niveaux de signature radar en monostatique, * amélioration de la couverture basse et très base altitude, * accroissement de la complexité des techniques de furtivité face à un tel radar, * discrétion (faible probabilité d'interception et d'exploitation), dans le domaine de l'emploi : * disparition des contraintes d'emploi d'un système rayonnant (dommages dus aux rayonnements sur le personnel, les armées et munitions, rayonnements non essentiels et compatibilité électromagnétique), * inutilité d'une allocation de fréquences, Enfin, dans le domaine du développement et du maintien en condition opérationnelle, une focalisation des coûts sur la partie réceptrice. Les méthodes de traitement spatio-temporel présentées sont génériques et peuvent est appliquées à toutes les formes d'onde. Le cas des émetteurs non coopératifs de télévision numérique terrestre est plus particulièrement étudié. Les propriétés radar de ce type d'émetteurs conduisent en effet à des capacités de détection accrues comparativement à d'autres types d'émetteurs de radiodiffusion (télephonie mobile, radio FM, radio numérique). L'étude de données réelles obtenues à partir d'un récepteur fixe (cible aérienne et marine) a non seulement conduit à développer une méthode spécifique de réjection du fouillis de sol et de localisation de cibles mais a également: * fourni de précieux renseignements sur la nature des environnements pouvant être rencontrés, * nourri la réflexion sur la façon d'adapter les traitements spatio-temporels adaptatifs à la nature particulière des signaux. Les éléments suivants sont présentés : * dans le cas d'un récepteur fixe: * développement, pour des formes d'onde quelconques, et validation sur signaux réels de type Digital Video Broadcasting Terrestrial (DVB-T), d'une méthode de réjection de fouillis et de localisation de cibles mobiles, * étude des propriétés statistiques de fouillis de sol, * dans le cas d'un récepteur mobile: * adaptation de méthodes spatio-temporelles de réjection de fouillis et comparaison de leurs performances respectives, * adaptation et généralisation au cas des cibles multiples et des antennes lacunaires de l'association d'une méthode de réjection en dimension réduite, la méthode Joint Domain Localized (JDL) et d'une méthode non-statistique focalisée sur la seule case distance- Doppler sous test, la méthode Direct Data Domain (D3), * développement d'une nouvelle méthode de réjection itérative du fouillis à partir des méthodes d'estimation spectrale.

<p><strong>This report presents concepts for a planar active electronically scanned antenna(AESA). The goal of the project was to devlop a low-weight, low profile, thin, S-band antenna with wide-scan angle capabilities. In the final concept the service aspects of the T/R-modules was also taken into acount in order to allow easy and fast replacements of these components. The antenna was designed and optimised using the commercial software Ansoft HFSS. A prototype of the antenna was constructed and later measured and verified. The final concept is a 2m×2m antenna with an estimated weight of around 320 kg, around 11 cm thick (where the thickness of the antenna element is 1.76 cm) and has a maximum scan angle range of more than 45 degrees (with <–10dB active reflection) in the frequency band 3–3.5 GHz. </strong></p>

Realistic assessment of the vertical distribution of clouds, particularly the occurrence of multi-layered systems, is critical for accurate calculations of radiative transfer in general circulation models. Such information is also useful in the design and improvement of satellite retrieval techniques. Current methods for retrieving cloud properties from satellite data assume that the clouds reside in single-layered systems. These methods are not expected to be successful for multi-layered systems. Attempts to specifically address the question of cloud layering have thus far been limited, due in part to the difficulties of inferring vertical cloud structure from either surface or satellite data. In situ observations, such as those provided by aircraft, are available only for localized regions and are limited in time. This study uses data from a lidar instrument flown onboard the space shuttle and satellite imagery data to identify the frequencies of occurrence of layered cloud systems at different spatial scales over various regions of the globe. The Lidar In-Space Technology Experiment (L1TE) was flown on Space Shuttle Discovery in September 1994 and provided global-scale, high vertical resolution profiles of the earth's troposphere and lower stratosphere. Analysis of the LITE observations requires distinguishing clouds residing in organized, well-defined layers from clouds that are distributed in altitude throughout the troposphere. The analysis employs a histogram technique in which peaks having some critical number of observations are considered to correspond to observations belonging to well-defined cloud layers. Advanced Very High Resolution Radiometer (AVHRR) data for the 11-day duration of the LITE mission are analyzed using the spatial coherence method. This method identifies regions of locally uniform emission which are associated either with cloud-free pixels or with overcast pixels corresponding to clouds in a single layer at a well-defined altitude. The number of layers present is determined by the number of overcast radiances associated with pixel arrays exhibiting locally uniform emission within the region. Layer statistics are compiled for the Pacific, Atlantic, and Indian Oceans and the North and South American, African, European, Asian, and Australian continents using horizontal scales of 60 and 250 km. The results indicate a strong dependence on the spatial scale chosen for the analysis, with two- and three-layered systems more prevalent at the 250-km scale. Analysis of cloud-top altitudes from LITE and AVHRR show that low-level cloud systems comprise the majority of the observations over both ocean and land. / Graduation date: 1998

Boundary layer (BL) stratocumulus clouds are an important factor in the earth's radiation budget due to their high albedo and low cloud top heights. Continental BL stratocumulus clouds are closely coupled to the diurnal cycle and the turbulence in the BL affecting the surface energy and moisture budgets. In this study the turbulence and mass-transport structures in continental BL stratocumulus clouds are studied using data from the Atmospheric Radiation Measurements (ARM)'s Southern Great Plains (SGP) observing facility located at Lamont, Oklahoma. High temporal (4 sec) and spatial (45 m) resolution observations from a vertically pointing 35 GHz cloud Doppler radar were used to obtain the in-cloud vertical velocity probability density function (pdf) in the absence of precipitation size hydrometeors. A total of 70 hours of radar data were analyzed to report halfhourly statistics of vertical velocity variance, skewness, updraft fraction, downdraft and velocity binned mass-flux at five cloud depth normalized levels. The variance showed a general decrease with increase in height in the cloud layer while the skewness is weakly positive in the cloud layer and negative near cloud top. The updraft fraction decreases with height with the decrease mainly occurring in the upper half of the cloud layer. The downdraft fraction increases with decrease in height with the increase being almost linear. The velocity of eddies responsible for maximum mass-transport decreases from of 0.4 ms-1 near cloud base to 0.2 ms-1 near cloud top. The half-hour periods were then classified based on the surface buoyancy flux as stable or unstable and it was found that the variance near cloud top is higher during the stable periods as compared to the unstable periods. Classification was also made based on the cloud depth to BL depth ratio (CBR) being greater or less than 0.3. The variance profile was similar for the classification while the skewness was almost zero during periods with CBR less 0.3 and positive during periods with CBR greater than 0.3. A 14 hour period of stratocumulus cloud on March 25, 2005 was analyzed to study the diurnal changes in the turbulence structure and mass transports. The variance near cloud base during the day time when the BL turbulence is primarily due to surface buoyancy production was higher than during the nighttime when the BL turbulence is driven by radiative cooling near the cloud top. Output from a one dimensional radiative transfer model was analyzed to study the vertical structure of the radiative fluxes. A radiative velocity scale analogous to the surface convective velocity scale is proposed to assess the relative importance of radiative cooling near cloud top in generating turbulence compared with the surface buoyancy production. An attempt was also made to calculate the hourly liquid water flux by combining the high temporal resolution (20 sec) liquid water content estimates from the radar reflectivity and a microwave radiometer with the radar observed vertical velocity. The liquid water flux was found to peak at a level below the cloud top and show a divergence with height that was similar to that from model simulations.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 23, 2007) Includes bibliographical references.

Two new stepped-frequency continuous wave (SFCW) radar sensor prototypes, based on a coherent super-heterodyne scheme, have been developed using Microwave Integrated Circuits (MICs) and Monolithic Millimeter-Wave Integrated Circuits (MMICs) for various surface and subsurface applications, such as profiling the surface and subsurface of pavements, detecting and localizing small buried Anti-Personnel (AP) mines and measuring the liquid level in a tank. These sensors meet the critical requirements for subsurface and surface measurements including small size, light weight, good accuracy, fine resolution and deep penetration. In addition, two novel wideband microstrip quasi-TEM horn antennae that are capable of integration with a seamless connection have also been designed. Finally, a simple signal processing algorithm, aimed to acquire the in-phase (I) and quadrature (Q) components and to compensate for the I/Q errors, was developed using LabView. The first of the two prototype sensors, named as the microwave SFCW radar sensor operating from 0.6-5.6-GHz, is primarily utilized for assessing the subsurface of pavements. The measured thicknesses of the asphalt and base layers of a pavement sample were very much in agreement with the actual data with less than 0.1-inch error. The measured results on the actual roads showed that the sensor accurately detects the 5-inch asphalt layer of the pavement with a minimal error of 0.25 inches. This sensor represents the first SFCW radar sensor operating from 0.6-5.6-GHz. The other sensor, named as the millimeter-wave SFCW radar sensor, operates in the 29.72-35.7-GHz range. Measurements were performed to verify its feasibility as a surface and sub-surface sensor. The measurement results showed that the sensor has a lateral resolution of 1 inch and a good accuracy in the vertical direction with less than  0.04-inch error. The sensor successfully detected and located AP mines of small sizes buried under the surface of sand with less than 0.75 and 0.08 inches of error in the lateral and vertical directions, respectively. In addition, it also verified that the vertical resolution is not greater than 0.75 inches. This sensor is claimed as the first Ka-band millimeter-wave SFCW radar sensor ever developed for surface and subsurface sensing applications.

Ground Penetrating Radar (GPR) is a near surface geophysical method that has been used for applications including archaeological sites, groundwater contamination, and geological mapping. Though GPR has been used extensively, advancements on data processing had a great impact on data resolution. GPR is frequently used for shallow investigations because of the high resolution near the surface; however, it has limited depth of penetration and vertical bed resolution. Vertical resolution is proportional to frequency. The thickness of beds in the subsurface is conventionally resolved to one-fourth the wavelength of the central frequency. The vertical resolution at a central frequency of 200 MHz in a beach environment is approximately 17 cm; however, that value does not accurately represent fine-scale lamina and pinching out of beds, which can be an order magnitude or more than the current resolution. Complex trace analysis and spectral analysis have been used in seismic reflection for characterizing structures and stratigraphy. These "attributes" have been used to indicate hydrocarbon presence in industry. The same concept was applied to a theoretical GPR model and tested against actual data. The theoretical GPR model was created to simulate a case in which two ideal 0 degree phase Ricker wavelets merge. The wavelets constructively "add" together to create a composite wavelet with double amplitude. Applying a spectral analysis reveals that an attribute in the form of instantaneous phase and instantaneous frequency can be used to image the beds merging. The spectral analysis was applied to field data from North Padre Island National Seashore, Texas, to image "pinch-outs". Multiple survey arrays were collected using a 200 MHz frequency antenna to image internal dune structures. The results showed anomalous features at merging beds and contacts between interfaces. The results directly influence sedimentological and geomorphological interpretations of internal dune structure and can be used to better understand erosional processes in coastal sedimentary environments.

The growing need for better definition of flow units and depositional heterogeneities in petroleum reservoirs and aquifers has stimulated a renewed interest in outcrop studies as reservoir analogues in the last two decades. Despite this surge in interest, outcrop studies remain largely two-dimensional; a major limitation to direct application of outcrop knowledge to the three dimensional heterogeneous world of subsurface reservoirs. Behind-outcrop Ground Penetrating Radar (GPR) imaging provides high-resolution geophysical data, which when combined with two dimensional architectural outcrop observation, becomes a powerful interpretation tool. Due to the high resolution, non-destructive and non-invasive nature of the GPR signal, as well as its reflection-amplitude sensitivity to shaly lithologies, three-dimensional outcrop studies combining two dimensional architectural element data and behind-outcrop GPR imaging hold significant promise with the potential to revolutionize outcrop studies the way seismic imaging changed basin analysis. Earlier attempts at GPR imaging on ancient clastic deposits were fraught with difficulties resulting from inappropriate field techniques and subsequent poorly-informed data processing steps. This project documents advances in GPR field methodology, recommends appropriate data collection and processing procedures and validates the value of integrating outcrop-based architectural-element mapping with GPR imaging to obtain three dimensional architectural data from outcrops. Case studies from a variety of clastic deposits: Whirlpool Formation (Niagara Escarpment), Navajo Sandstone (Moab, Utah), Dunvegan Formation (Pink Mountain, British Columbia), Chinle Formation (Southern Utah) and St. Mary River Formation (Alberta) demonstrate the usefulness of this approach for better interpretation of outcrop scale ancient depositional processes and ultimately as a tool for refining existing facies models, as well as a predictive tool for subsurface reservoir modelling. While this approach is quite promising for detailed three-dimensional outcrop studies, it is not an all-purpose panacea; thick overburden, poor antenna-ground coupling in rough terrains typical of outcrops, low penetration and rapid signal attenuation in mudstone and diagenetic clay- rich deposits often limit the prospects of this novel technique.

In 2011, the Canadian enhanced Polar Outflow Probe (ePOP) satellite will be launched. The ePOP satellite is equipped with several scientific Earth observation instruments, including a Radio Receiver Instrument (RRI) which will be used to detect High Frequency (HF) radio waves transmitted from a ground-based transmitter. The ground-based instrument will be one of the Super Dual Auroral Radar Network (SuperDARN) array of radars. A radio wave transmitted from the SuperDARN radar will propagate through the ionosphere and be detected by the RRI on ePOP. Analysis of the characteristics of the signal received by the RRI will provide information about the plasma density in the ionosphere between the transmitter and receiver. As the ePOP satellite is not yet operational, extensive ray path modelling has been performed to simulate the expected signal at the RRI for various ionospheric conditions.<p> The other major objective of this research was to examine the effect of the variable refractive index in the ionosphere on SuperDARN drift velocity measurements. Past comparisons between velocities measured by SuperDARN and other instruments have found that velocities measured by SuperDARN typically were about 20-30% lower. This research has shown that underestimation of drift velocities by SuperDARN is a consequence of not including the refractive index when these velocities are calculated. As refractive index measurements are not readily available, this research has involved developing and implementing various methods to estimate the refractive index in the ionosphere. These methods have demonstrated that plasma density values within the SuperDARN scattering volume are appreciably higher than background plasma densities in the ionosphere. Application of these methods, which has resulted in a much better understanding of the physics of the coherent scattering process, has resulted in agreement between velocities measured by SuperDARN and other instruments.