Convective clouds in the tropics can be grouped into three categories: shallow clouds with cloud-top heights near 2 km above the surface, mid-level congestus clouds with tops near the 0°C level, and deep convective clouds capped by the tropopause. This trimodal distribution is visible in cloud data from the Geoscience Laser Altimeter System (GLAS), carried aboard the Ice, Cloud, and land Elevation Satellite (ICESat), as well as in precipitation data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). Fractional areal coverage (FAC) data is calculated at each of the three levels to describe how often optically thick clouds or precipitation are seen at each level. By dividing the FAC of TRMM PR-observed precipitation by the FAC of thick GLAS/ICESat-observed clouds, the fraction of clouds that are precipitating is derived. The tropical mean precipitating cloud fraction is low: 3.7% for shallow clouds, 6.5% for mid-level clouds, and 24.1% for deep clouds. On a regional basis, the FAC maps created in this study show interesting trends. The presence of nonphysical answers in the PCF graphs, however, suggest that greater study with more precise instruments is needed to properly understand the true precipitating cloud fraction of the tropical atmosphere.

OSIRIS, a Canadian built instrument on-board the Swedish-led remote sensing satellite, Odin, consists in part of three single lens imagers that measure near infrared light from atmospheric scattering and emission. A full calibration of the imaging system is required to remove all instrument dependent effects that modify the observations. <p>This work presents the characterization and calibration of the OSIRIS imaging system in an attempt to produce observations that are instrument independent measurements of the atmospheric brightness. The required product is the number of photons per second emitted, or scattered, from the atmosphere that are within the sampling wavelength range and incident on the detector area in the instrument field of view. <p>A major portion of the present work involves understanding the dark current production mechanisms and the development of a technique to characterize the dark current and manufacturer imposed electronic offsets. It is demonstrated that with a current set of dark calibration images, the developed algorithm effectively removes the dark current and electronic offsets over a wide operating temperature range. The relative calibration of pixels is presented in terms of the electronic gain, or flat field response, and the angular look direction. It is apparent that a change in the relative pixel gain occurred between pre-flight calibration and the first in-flight images. However, it is shown that with a recalculation of the flat field response using in-flight images, an acceptable gain calibration is obtained. The angular look direction of the pixels is determined from the results of two separate in-flight experiments. The characterization and removal of the stray light signal is shown to be effective. <p>Finally, the absolute calibration of the instrument is presented. While several issues remain to be addressed, the comparison with a simple atmospheric brightness model provides a first order verification of the results.

OSIRIS, a Canadian built instrument on-board the Swedish-led remote sensing satellite, Odin, consists in part of three single lens imagers that measure near infrared light from atmospheric scattering and emission. A full calibration of the imaging system is required to remove all instrument dependent effects that modify the observations. <p>This work presents the characterization and calibration of the OSIRIS imaging system in an attempt to produce observations that are instrument independent measurements of the atmospheric brightness. The required product is the number of photons per second emitted, or scattered, from the atmosphere that are within the sampling wavelength range and incident on the detector area in the instrument field of view. <p>A major portion of the present work involves understanding the dark current production mechanisms and the development of a technique to characterize the dark current and manufacturer imposed electronic offsets. It is demonstrated that with a current set of dark calibration images, the developed algorithm effectively removes the dark current and electronic offsets over a wide operating temperature range. The relative calibration of pixels is presented in terms of the electronic gain, or flat field response, and the angular look direction. It is apparent that a change in the relative pixel gain occurred between pre-flight calibration and the first in-flight images. However, it is shown that with a recalculation of the flat field response using in-flight images, an acceptable gain calibration is obtained. The angular look direction of the pixels is determined from the results of two separate in-flight experiments. The characterization and removal of the stray light signal is shown to be effective. <p>Finally, the absolute calibration of the instrument is presented. While several issues remain to be addressed, the comparison with a simple atmospheric brightness model provides a first order verification of the results.

<p>Centromeres, or sites of chromosomal spindle attachment during mitosis and meiosis, are non-randomly distributed in complex genomes and are largely associated with expansive, near-identical satellite DNA arrays. While the sequence basis of centromere identity remains a subject of considerable debate, one approach is to examine the genomic organization of satellite DNA arrays and their potential function. Current genome assembly and sequence annotation strategies, however, are dependent on robust sequence variation, and, as a result, these regions of near sequence identity remain absent from current genome reference sequences and thus are detached from explorations of centromere biology. This dissertation is designed as a foundational study for centromere genomics, providing the initial steps to characterize those sequences at endogenous centromeres, while further classifying `functional' sequences that directly interact with, or are capable of recruiting proteins involved in, centromere function. These studies build on and take advantage of the limited sequence variation in centromeric satellite DNA, providing the necessary genomic scope to promote biologically meaningful characterization of endogenous centromere sequences in both human and non-human genomes. As a result, this thesis demonstrates possible genomic standards for future studies in the emerging field of satellite biology, which is now positioned to address functional centromere sequence variation across evolutionary time.</p> / Dissertation

Convective clouds in the tropics can be grouped into three categories: shallow clouds with cloud-top heights near 2 km above the surface, mid-level congestus clouds with tops near the 0°C level, and deep convective clouds capped by the tropopause. This trimodal distribution is visible in cloud data from the Geoscience Laser Altimeter System (GLAS), carried aboard the Ice, Cloud, and land Elevation Satellite (ICESat), as well as in precipitation data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). Fractional areal coverage (FAC) data is calculated at each of the three levels to describe how often optically thick clouds or precipitation are seen at each level. By dividing the FAC of TRMM PR-observed precipitation by the FAC of thick GLAS/ICESat-observed clouds, the fraction of clouds that are precipitating is derived. The tropical mean precipitating cloud fraction is low: 3.7% for shallow clouds, 6.5% for mid-level clouds, and 24.1% for deep clouds. On a regional basis, the FAC maps created in this study show interesting trends. The presence of nonphysical answers in the PCF graphs, however, suggest that greater study with more precise instruments is needed to properly understand the true precipitating cloud fraction of the tropical atmosphere.

Formation flying is a new satellite mission concept that is concerned with clusters of satellites in neighboring orbits cooperating to perform a specific task. The tasks may be Earth observation or space-based interferometry where a cluster of small satellites is able to fulfill the same requirements as that of a larger, monolithic satellite. There exist a variety of models for the study of relative motion between two satellites. These include models based upon differential orbital elements, and relative position and velocity coordinates. Extensive work has been done on such models, both in the absence and presence of the J2 perturbation arising from the aspherical nature of the Earth, which causes variations in the orbital elements that describe the orbit. The approximate relative motion can be obtained analytically by using mean elements. However, the true orbit can only be described by the instantaneous osculating elements. An analytical method to propagate the relative motion between two satellites in highly elliptic orbits is the main focus of this thesis. The method is kinematically exact and it maintains a high degree of accuracy even in the presence of J2 perturbations. Mean orbital elements are used for orbit propagation, and expansions involving the powers of eccentricity are not utilized. The true anomaly of the reference satellite is treated as the independent variable, instead of time. The relative orbit kinematics are obtained by using a projection onto a unit sphere. This procedure allows the relative position variables to be treated as angles depending on the orbital element differences. The effect of adding short-period corrections due to J2 to the mean elements is also studied. Finally, the problem of formation reconfiguration is studied. The reconfiguration of a formation may be achieved by using impulsive thrust (velocity increments) or continuous control. This thesis presents a method to obtain the optimal velocity increments through numerical optimization, utilizing the analytical technique developed for relative orbit propagation. A continuous control law is also developed using a candidate Lyapunov function, and the asymptotic stability of the closed-loop system is ascertained.

The Antarctic ice sheet mass budget is a very important factor for global sea level. An understanding of the glacial dynamics of the Antarctic ice sheet are essential for mass budget estimation. Utilizing a surface velocity field derived from Radarsat three-pass SAR interferometry, this study has investigated the strain rate, grounding line, balance velocity, and the mass balance of the entire Lambert Glacier – Amery Ice Shelf system, East Antarctica. The surface velocity increases abruptly from 350 m/year to 800 m/year at the main grounding line. It decreases as the main ice stream is floating, and increases to 1200 to 1500 m/year in the ice shelf front. The strain rate distribution defines the shear margins of ice flows. The major ice streams and their confluence area experience the most severe ice deformation. The width of the shear margin decreases as it flows downstream except for the convergent areas with tributary glaciers. The grounding line for the main ice stream and the boundary of Amery Ice Shelf and surrounding tributary glaciers is delineated. The total basal melting is estimated to be 87.82 ± 3.78 Gt/year for the entire Amery Ice Shelf. Compared with the ice flux (16.35 ± 3.11 Gt/year) at the ice shelf front, basal melting is apparently the dominant discharging process of the system. The melting rate for the Amery Ice Shelf decreases rapidly from the grounding zone (21.64 ± 2.17 m/year) to the ice shelf front (-0.95 ± 0.14 m/year). The Lambert Glacial Basin contributes the total ice mass of 95.64 ± 2.89 Gt/year to the ocean, which is equivalent to increasing the global sea level by 0.24 mm/year. Considering 90.54 ± 1.55 Gt/year of snow accumulation, the entire Lambert Glacier – Amery Ice Shelf system is slightly negatively imbalanced at -5.09 ± 3.46 Gt/year. Although the entire system is estimated to have a slight negative mass balance, three sub-glacial systems have a net positive mass balance due to a relatively high snow accumulation rate or relatively slow ice motion. Considering the large mass loss in West Antarctica, it is believed that the overall mass budget in Antarctica is negative based on this research.

This thesis investigates the variation of the chlorophyll-a concentration near Dongsha Atoll derived from MODIS Aqua and Terra satellite images, and their relationship to physical environments including sea surface temperature, CTD water qualities, tides, currents and surface winds for the period 2005 to 2008. The results revealed that the seasonal variation of chlorophyll-a concentration was higher in the winter than in the summer, and had inverse relationship with sea surface temperature. The increased chlorophyll-a concentration was due to entrainment of lower layer cold water with high nutrient. The upwelling water was induced by mixing of surface wind and internal wave shoaling. When the internal waves propagated westward to the Dongsha Atoll, the bottom topography and coastline oriented the cold deep water surged up slope to the northeastern corner of the Atoll, which produced high chlorophyll-a concentration a few days after. The comparison of MODIS images and CTD data revealed that the chlorophyll-a concentration didn¡¦t increase immediately after the passage of internal waves.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 198 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Christopher Jekeli, Dept. of Geodetic Science and Surveying. Includes bibliographical references (p. 192-198).

No description available.