Time Domain SAR Processing with GPUs for Airborne Platforms

A time-domain backprojection processor for airborne synthetic aperture radar (SAR) has been developed at the University of Massachusetts’ Microwave Remote Sensing Lab (MIRSL). The aim of this work is to produce a SAR processor capable of addressing the motion compensation issues faced by frequency-domain processing algorithms, in order to create well focused SAR imagery suitable for interferometry. The time-domain backprojection algorithm inherently compensates for non-linear platform motion, dependent on the availability of accurate measurements of the motion. The implementation must manage the relatively high computational burden of the backprojection algorithm, which is done using modern graphics processing units (GPUs), programmed with NVIDIA’s CUDA language. An implementation of the Non-Equispaced Fast Fourier Transform (NERFFT) is used to enable efficient and accurate range interpolation as a critical step of the processing. The phase of time- domain processed imagery is dif erent than that of frequency-domain imagery, leading to a potentially different approach to interferometry. This general purpose SAR processor is designed to work with a novel, dual-frequency S- and Ka-band radar system developed at MIRSL as well as the UAVSAR instrument developed by NASA’s Jet Propulsion Laboratory. These instruments represent a wide range of SAR system parameters, ensuring the ability of the processor to work with most any airborne SAR. Results are presented from these two systems, showing good performance of the processor itself

Gravitational Wave Astrophysics: Instrumentation, Detector Characterization, and a Search for Gravitational Signals from Gamma-ray Bursts

In the coming years, the second generation of interferometric gravitational wave detectors are widely expected to observe the gravitational radiation emitted by compact, energetic events in the nearby universe. The field of gravitational wave astrophysics has grown into a large international endeavor with a global network of kilometer-scale observatories. The work presented in this thesis spans the field, from optical metrology, to instrument commissioning, to detector characterization and data analysis. The principal results are a method for the precise characterization of optical cavities, the commissioning of the advanced LIGO Output Mode Cleaner at the Hanford observatory, and a search for gravitational waves associated with gamma-ray bursts

Design and Development of a Ka-band Interferometer for Cryospheric Applications

Topographic maps of the earth are essential to geographic and earth science studies. In particular, mapping and estimating physical parameters of the earth’s water and ice cover are critical to global climate studies. Among these, snow, ocean and fresh water topography, snow wetness and water equivalent are of immediate interest to the scientific community. Challenges in the instrument development and deployment posed by these required measurements are twofold. Firstly, these measurements are required to have global coverage, yet maintain stringent spatial resolution and accuracy margins. Secondly, snow topography measurement requires minimal electromagnetic wave penetration through snow, hence requiring the use of millimeter-wave frequency radars. While having the advantage of smaller and lighter structures, instruments at millimeter-wave frequencies are difficult to design, evaluate and deploy due to their mechanical and electric precision requirements. This thesis presents the design, development, detailed evaluation and first deployment of a Ka-band interferometer. An overview of the theory of interferometric mapping is presented including a discussion on instrument sensitivity and accuracy. Based in this theory, a geometric and hardware configuration for a rooftop deployment is arrived at. Detailed design and evaluation of the radar receiver is documented. Lastly first results from a rooftop and ground-based deployment are presented

InSAR Simulations for SWOT and Dual Frequency Processing for Topographic Measurements

In Earth remote sensing precise characterization of the backscatter coefficient is important to extract valuable information about the observed target. A system that eliminates platform motion during near-nadir airborne observations is presented in this thesis, showing an improvement on the accuracy of measurements for a Ka- band scatterometer previously developed at Microwave Remote Sensing Laboratory (MIRSL). These very same results are used to simulate the reflectivity of such targets as seen from a spaceborne radar and estimate height errors based on mission-specific geometry. Finally, data collected from a dual-frequency airborne interferometer com- prised by the Ka-band system and an S-band radar is processed and analyzed to estimate forest heights

Advancing spaceborne tools for the characterization of planetary ionospheres and circumstellar environments

This work explores remote sensing of planetary atmospheres and their circumstellar surroundings. The terrestrial ionosphere is a highly variable space plasma embedded in the thermosphere. Generated by solar radiation and predominantly composed of oxygen ions at high altitudes, the ionosphere is dynamically and chemically coupled to the neutral atmosphere. Variations in ionospheric plasma density impact radio astronomy and communications. Inverting observations of 83.4 nm photons resonantly scattered by singly ionized oxygen holds promise for remotely sensing the ionospheric plasma density. This hypothesis was tested by comparing 83.4 nm limb profiles recorded by the Remote Atmospheric and Ionospheric Detection System aboard the International Space Station to a forward model driven by coincident plasma densities measured independently via ground-based incoherent scatter radar. A comparison study of two separate radar overflights with different limb profile morphologies found agreement between the forward model and measured limb profiles. A new implementation of Chapman parameter retrieval via Markov chain Monte Carlo techniques quantifies the precision of the plasma densities inferred from 83.4 nm emission profiles. This first study demonstrates the utility of 83.4 nm emission for ionospheric remote sensing. Future visible and ultraviolet spectroscopy will characterize the composition of exoplanet atmospheres; therefore, the second study advances technologies for the direct imaging and spectroscopy of exoplanets. Such spectroscopy requires the development of new technologies to separate relatively dim exoplanet light from parent star light. High-contrast observations at short wavelengths require spaceborne telescopes to circumvent atmospheric aberrations. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) team designed a suborbital sounding rocket payload to demonstrate visible light high-contrast imaging with a visible nulling coronagraph. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space. These two studies advance our ``close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system

The Atmospheric Imaging Radar for High Resolution Observations of Severe Weather

Mobile weather radars often utilize rapid scan strategies when collecting obser- vations of severe weather. Various techniques have been used to improve volume update times, including the use of agile and multi-beam radars. Imaging radars, similar in some respects to phased arrays, steer the radar beam in software, thus requiring no physical motion. In contrast to phased arrays, imaging radars gather data for an entire volume simultaneously within the field-of-view of the radar, which is defined by a broad transmit beam. As a result, imaging radars provide update rates significantly exceeding those of existing mobile radars, including phased arrays. The Atmospheric Radar Research Center at the University of Oklahoma is engaged in the design, construction and testing of a mobile imaging weather radar system called the Atmospheric Imaging Radar (AIR).Initial tests performed with the AIR demonstrate the benefits and versatility of utilizing beamforming techniques to achieve high spatial and temporal resolution. Specifically, point target analysis was performed using several digital beamform- ing techniques. Adaptive algorithms allow for the improved resolution and clutter rejection when compared to traditional techniques. Additional experiments were conducted during three severe weather events in Oklahoma, including an isolated cell event with high surface winds, a squall line, and a non-tornadic cyclone. Sev- eral digital beamforming techniques were tested and analyzed, producing unique, simultaneous multi-beam measurements using the AIR.The author made specific contributions to the field of radar meteorology in several areas. Overseeing the design and construction of the AIR was a signif- icant effort and involved the coordination of many smaller teams. Interacting with the members of each group and ensuring the success of the project was a primary focus throughout the venture. Meteorological imaging radars of the past have typically focused on boundary layer or upper atmospheric phenomena. The AIR's primary focus is to collect precipitation data from severe weather. Ap- plying well defined beamforming techniques, ranging from Fourier to adaptive algorithms like robust Capon and Amplitude and Phase Estimation (APES), to precipitation phenomena was a unique effort and has served to advance the use of adaptive array processing in radar meteorology. Exploration of irregular antenna spacing and drawing from the analogies between temporal and spatial process- ing led to the development of a technique that reduced the impact of grating lobes by unwrapping angular ambiguities. Ultimately, the author leaves having created a versatile platform capable of producing some of the highest resolution weather data available in the research community today, with opportunities to significantly advance the understanding of rapidly evolving weather phenomena and severe storms

The ESPAS e-infrastructure

ESPAS provides an e-Infrastructure to support access to a wide range of archived observations and model derived data for the near-Earth space environment, extending from the Earth's middle atmosphere up to the outer radiation belts. To this end, ESPAS will serve as a central access hub for researchers who wish to exploit multi-instrument multipoint data for scientific discovery, model development and validation, and data assimilation, among others. Observation based and model enhanced scientific understanding of the physical state of the Earth's space environment and its evolution is critical to advancing space weather and space climate studies, two very active branches of current scientific research. ESPAS offers an interoperable data infrastructure that enables users to find, access, and exploit near-Earth space environment observations from ground-based and spaceborne instruments and data from relevant models, obtained from distributed repositories. In order to facilitate efficient user queries ESPAS allows a highly flexible workflow scheme to select and request the desired data sets. ESPAS has the strategic goal of making Europe a leading player in the efficient use and dissemination of near-Earth space environment information offered by institutions, laboratories and research teams in Europe and worldwide, that are active in collecting, processing and distributing scientific data. Therefore, ESPAS is committed to support and foster new data providers who wish to promote the easy use of their data and models by the research community via a central access framework. ESPAS is open to all potential users interested in near-Earth space environment data, including those who are active in basic scientific research, technical or operational development and commercial applications

The role of molecular clouds in the star formation process as observed in two grand design spiral galaxies.

We have compared the molecular, neutral and ionized hydrogen distributions in two nearby spiral galaxies. To estimate H\sb2 surface densities we acquired observations of the CO (J = 1 $\to$ 0) transition in 60 positions to a radius of 135 in the Sbc galaxy M51 (NGC 5194), and in 21 positions to a radius of 150 in the SAB galaxy M83 (NGC 5236) using the 13.7 m telescope of the Five College Radio Astronomy Observatory. The molecular component of the ISM was found to strongly dominate over the HI component in each galaxy. Extinction corrected H$\alpha$ intensities were used to compute the detailed massive star formation rates (MSFRs) in each galaxy. Estimates of the MSFR, gas density, and the ratio of these quantities, the massive star formation efficiency (MSFE), were then examined. In M51, the spiral arms exhibit an excess gas density of 1.4-1.6 times the interarm values. The MSFR contrast between the arms and interarms, measuring between 1.5 and 2.3 at the same resolution, exceeds the gas density contrast and implies a nonlinear relationship between star formation and gas surface density on the spiral arms. This follows the predictions of the cloud-cloud collision scenario fo star formation which relies on the occurrence of orbit crowding to bring clouds into close proximity. We note that the regions exhibiting the highest MSFEs are those in the spiral potential minimum inward of R = 124 , and those regions outward of R = 124 thought to be experiencing orbit crowding due to tidal distortion caused by the close passage of M51\u27s companion galaxy. The total (arm and interarm) gas content and massive star formation rates in concentric annuli in the disk of M51 were computed. The two quantities fall off together with radius, yielding a relatively constant MSFE with radius. This is consistent with the increased MSFE on the arms in that the majority of the gas shows a constant MSFE. The resulting time scale for gas depletion (total SFE\sp{-1}) in the disk is 2.5 $\pm$ 5 $\times$ 10\sp9 yr assuming a Salpeter-like initial mass function. In M83, the molecular gas component of the inner disk mimics the bar morphology. In this galaxy there is the suggestion of enhanced star formation at the ends of the central bar due to the compression of cloud orbits found there. The gas depletion time scale is 1.2 $\pm$ 0.3 $\times$ 10\sp9 yr

The impact of terrestrial noise on the detectability and reconstruction of gravitational wave signals from core-collapse supernovae

Among of the wide range of potentially interesting astrophysical sources for gravitational wave detectors Advanced LIGO and Advanced Virgo are galactic core-collapse supernovae. Although detectable core-collapse supernovae have a low expected rate (a few per century, or less) these signals would yield a wealth of new physics. Of particular interest is the insight into the explosion mechanism driving core-collapse supernovae that can be gleaned from the reconstructed gravitational wave signal. A well-reconstructed waveform will allow us to assess the likelihood of different explosion models, perform model selection, and potentially map unexpected features to new physics. This dissertation presents a series of studies evaluating the current performance of burst parameter estimation algorithms in reconstructing core-collapse supernovae gravitational wave signals in both simple Gaussian noise and realistic non-Gaussian detector noise. The introduction of non-Gaussian noise has a significant impact on the recovery of core-collapse supernova models from the data. Terrestrial noise is also an important factor in the recovery of any gravitational wave search. This work also details a series of studies that enable the characterization of ground motion local to the Advanced LIGO inteferometers and the ability of the installed active seismic isolation to mitigate it