Parallel high-precision orbit propagation using the modified Picard-Chebyshev method

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3590. Adviser: Jonathan B. Freund. Includes bibliographical references (leaves 95-98) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Gary Harlow.

<p>Global Navigation Satellite System (GNSS) radio occultation (RO) is a remote sensing technique that exploits existing navigation signals to make global, real-time observations of the Earth's atmosphere. A specialized RO receiver makes measurements of signals originating from a transmitter onboard a GNSS spacecraft near the Earth's horizon. The radio wave is altered during passage through the Earth's atmosphere. The changes in the received signals are translated to the refractivity characteristics of the intervening medium, which enable the calculation of atmospheric pressure, temperature, and humidity. Current satellite missions employing GNSS RO have provided invaluable and timely information for weather and climate applications. Existing constellations of occultation satellites, however, are aging and producing fewer quality measurements. Replacement fleets of RO satellites are imperative to sustain and improve the global coverage and operational impact achieved by the current generation of RO satellites. This dissertation describes studies that facilitate the development of next generation RO receivers and satellite constellations. Multiple research efforts were conducted that aim to improve the quantity and quality of measurements made by a future satellite-based RO collection system. These studies range in magnitude and impact, and begin with a receiver development study using ground-based occultation data. Future RO constellations and collection opportunities were simulated and autonomous occultation prediction and scheduling capabilities were implemented. Finally, a comprehensive study was conducted to characterize the stability of the GNSS atomic frequency standards. Oscillator stability for a subset of satellites in the GNSS was found to be of insufficient quality at timescales relevant to RO collections and would degrade the atmospheric profiling capabilities of an RO system utilizing these signals. Recommendations for a high-rate clock correction network are proposed, which provides significant improvement to the fractional errors in the derived refractivity, pressure, and temperature values caused by the oscillator instabilities.

This dissertation deals with modeling the radiative regime in vegetation canopies and the possible remote sensing applications derived by solving the forward and inverse canopy transport equation. The aim of the research is to develop a methodology (called "end-to-end problem solution") that, starting from first principles describing the interaction between light and vegetation, constructs, as the final product, a tool that analyzes remote sensing data for precision agriculture (ripeness prediction). The procedure begins by defining the equations that describe the transport of photons inside the leaf and within the canopy. The resulting integro-differential equations are numerically integrated by adapting the conventional discrete-ordinate methods to compute the reflectance at the top of the canopy. The canopy transport equation is also analyzed to explore its spectral properties. The goal here is to apply Case's method to determine eigenvalues and eigenfunctions and to prove completeness. A model inversion is attempted by using neural network algorithms. Using input-outputs generated by running the forward model, a neural network is trained to learn the inverse map. The model-based neural network represents the end product of the overall procedure. During Oct 2002, an Unmanned Aerial Vehicles (UAVs) equipped with a camera system, flew over Kauai to take images of coffee field plantations. Our goal is to predict the amount of ripe coffee cherries for optimal harvesting. The Leaf-Canopy model was modified to include cherries as absorbing and scattering elements and two classes of neural networks were trained on the model to learn the relationship between reflectance and percentage of ripe, over-ripe and under-ripe cherries. The neural networks are interfaced with images coming from Kauai to predict ripeness percentage. Both ground and airborne images are considered. The latter were taken from the on-board Helios UAV camera system flying over the Kauai coffee field. The results are compared against hand counts and parchment data to evaluate the network performances on real applications. In ground images, the error is always less than 11%. In airborne image, the error bound is 20%. The results are certainly adequate and show the tremendous potential of the methodology.

This work is aimed at developing a methodology for inspecting large plates, used in civil infrastructure, by Lamb waves. The traditional methods inspecting infrastructure are based on scattering of elastic waves from internal defects and on time of flight measurements. The methods based on elastic wave scattering can only detect defects larger than the wavelength of ultrasound used. The time of flight measurements have proven to be unreliable for strength analysis. This work investigates the potential of the Lamb wave technique to detect small defects when Lamb waves propagate over large distances. An innovative transducer holder setup is developed, which is the key to how Lamb waves can be generated and received in large structures.

A new stiffened shell element combining shallow beam and shallow shell elements is developed for geometrically nonlinear analysis of stiffened composite laminates under thermal and/or mechanical loading. The formulation of this element is based on the principal of virtual displacements in conjunction with the co-rotational form of the total Lagrangian description of motion. In the finite element formulation, both the shell and the beam (stiffener) elements account for transverse shear deformations and material anisotropy. The cross-section of the stiffener (beam) can be arbitrary in geometry and lamination. In order to combine the stiffener with the shell element, constraint conditions are applied to the displacement and rotation fields of the stiffener. These constraint conditions ensure that the cross-section of the stiffener remains co-planar with the shell section after deformation. The resulting expressions for the displacement and rotation fields of the stiffener involve only the nodal unknowns of the shell element, thus reducing the total number of degrees of freedom. Also, the discretization of the entire stiffened shell structure becomes more flexible.

As the field of remote sensing continues to grow with the launches of many new and complex satellite sensors in the next year, the ability to provide absolute calibration of these sensors becomes paramount for the many environmental studies proposed. In particular, temporal studies that monitor global changes in atmospheric constituents, ocean and terrestrial temperatures, and vegetation require that changes in the sensor itself, over the period of the study, be understood so that the data may be corrected. Numerous studies have established that satellite sensors change in orbit with respect to preflight calibration, in some cases, up to 20% or more over periods of three years. This research describes the development of an improved cross-calibration method of on-orbit satellite sensor radiometric calibration. The objective of the cross-calibration method is to transfer one sensor's calibration to another sensor which is typically difficult or expensive to calibrate with other methods. The cross-calibration method is relatively inexpensive to apply, and therefore there was a strong incentive to improve the application of the method and the understanding of the uncertainties associated with the method. The primary effort in this work has been the development of a cross-calibration software program which provides the means to easily perform end-to-end cross-calibrations. The program allows for a multiplicity of sites to be run, provides a search mechanism in order to identify calibration sites with particular characteristics, and contains an extensive error analysis capability. As part of this work, a search for acceptable cross-calibration sites was also performed which would allow a reduction in uncertainties of the method. Calibrations of five different sensor band pairs using System Pour l'Observation de la Terre (SPOT) 3, Landsat Thematic Mapper, and Advanced Very High Resolution Radiometer (AVHRR) sensors are performed. Very good results are obtained when the results are compared with other more expensive calibration methods, and the calibrations yielded uncertainties lower than reported in previous work.

Recent efforts in Earth remote sensing have focused on accurately measuring top-of-atmosphere and surface leaving radiances. One factor that must be accounted for in the radiometric calibration of an Earth remote sensing satellite is the polarization of the radiance. This dissertation provides a comprehensive analysis of how polarization has an impact on the radiometric calibration of visible through long wave infrared Earth remote sensing satellites (0.4 through ∼15 μm). The first part of this dissertation concentrates on reviewing the current status of calibration and of polarization measurements in Earth remote sensing. It provides a comprehensive review of polarization in Earth scenes, calibration targets, and the sensitivity of instruments. The second part examines how polarization affects calibration during the application of the calibration coefficients. One must account for the differences in polarization between the calibration target, used to determine the calibration coefficients, and the scene itself. This dissertation derives the impact of polarization on the radiometric calibration coefficients using both the Stokes vector and the Jones vector formalisms and accounts for the instrument polarization sensitivity, calibration target polarization, and scene polarization through normalization. Using these derived results, the impacts of polarization on radiometric uncertainty are calculated for the family of theoretical cases and for cases based on literature data. The third part of this dissertation examines how the polarization response of an instrument can affect the calibration by creating a variation in the response vs. scan angle (RVS). It derives the mathematical relationship between the polarization response of an instrument and its response vs. scan angle. It examines the correlation between the two using MODIS pre-launch system level polarization and RVS measurement data and derives the sensitivity of the RVS to aft optics polarization. This establishes when scan mirror data is sufficient to characterize RVS and when a system level measurement is required. This dissertation then examines potential ways to determine the instrument's polarization response and response vs. scan angle post-launch. Finally, this dissertation identifies sensitivity thresholds in both cases and summarizes when polarization should be accounted for in radiometric calibration. Potential areas for future advancement of the field are discussed.

The wake of an axisymmetric bluff body was investigated using water tunnel experiments. The parameters common to all investigations were a Reynolds number of 1000 or 1500 based on the body diameter, and a boundary layer thickness entering the body base of 30% of the base diameter. Harmonic forcing was accomplished using eight individual piston pump actuators providing blowing and suction disturbances into the boundary layer close to the body base, or into the wake at the base of the body. This setup allowed the excitation of azimuthal mode numbers up to four. The resulting flow field was evaluated using flow visualization, single wire hot film anemometry, and direct drag force measurements. Four different helical mode combinations were used to force the wake, ±1, ±2, ±3, and ±4. The ±1 modes are dominant in the natural wake. When forcing the ±1 modes it was possible to lock their frequency and phase to the forcing over a relatively large frequency range. Within the lock-in range, the wake drag increased by up to 40%. The mean flow of the wake was axisymmetric. Forcing the ±2 modes, the lock-in frequency range was significantly smaller and was centered at somewhat higher frequencies. The mean flow in this case was distorted to a four-lobed polygon, and the drag increased by more than 60%. The ±3 forcing yielded a flow response that involved neighboring modes with significant amplitudes, which was most likely caused by the decreased quality of the spatial representation of the forcing input due to the limited number of pistons. The combination of the different modes resulted in a mean flow distortion and amplitude distribution with five lobes. The frequency range for which lock-in could be observed was further reduced when compared to the ±2 case. For forcing modes ±4, the flow responded only locally to the forcing, and the decay of the forced modes in downstream direction was very rapid, for example, at three diameters downstream the forced modes were no longer detectable.