Mountain Scholar :: Browsing by Author "Notaros, Branislav, committee member"

Browsing by Author "Notaros, Branislav, committee member"

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Open Access
A CMOS compatible optical biosensing system based on local evanescent field shift mechanism
(Colorado State University. Libraries, 2011) Yan, Rongjin, author; Lear, Kevin L., advisor; Dandy, David S., committee member; Chandrasekar, V., committee member; Notaros, Branislav, committee member
The need for label-free integrated optical biosensors has dramatically increased in recent years. Integrated optical biosensors have many advantages, including low-cost, and portability. They can be applied to many fields, including clinical diagnostics, food safety, environmental monitoring, and biosecurity applications. One of the most important applications is point-of-care diagnosis, which means the disease could be tested at or near the site of patient care rather than in a laboratory. We are exploring the issues of design, modeling and measurement of a novel chip-scale local evanescent array coupled (LEAC) biosensor, which is an ideal platform for point-of-care diagnosis. Until now, three generations of LEAC samples have been designed, fabricated and tested. The 1st generation of LEAC sensor without a buried detector array was characterized using a commercial near field scanning optical microscope (NSOM). The sample was polished and was end-fire light coupled using single mode fiber. The field shift mechanism in this proof-to-concept configuration without buried detector arrays has been validated with inorganic adlayers [1], photoresist [2] and different concentrations of CRP proteins [3]. Mode beating phenomena was predicted by the beam propagation method (BPM) and was observed in the NSOM measurement. A 2nd generation LEAC sensor with a buried detector array was fabricated using 0.35μm CMOS process at the Avogo Technologies Inc., Fort Collins, Colorado. Characterizations with both single layer patternings, including photoresist as well as BSA [4] and immunoassay complexes [5] were done with cooperative efforts from various research groups. The BPM method was used to study the LEAC sensor, and the simulation results demonstrated the sensitivity of the LEAC sensor is 16%/nm, which was proved to match well with the experimental data [6]. Different antigen/antibodies, including mouse IgG and Hspx (a tuberculosis reactive antigen), have been used to test the immunoassay ability of LEAC sensor [7]. Many useful data have been collected by using the 2nd generation LEAC chip. However, during the characterization of the Avago chips, some design problems were revealed, including incompatibility with microfluidic integration, restricted detection region, strong sidewall scattering and uncoupled light interference from the single mode fiber. To address these problems, the 3rd generation LEAC sensor chip with buried detector arrays was designed to allow real-time monitoring and compatibility with microfluidic channel integration. 3rd generation samples have been fabricated in the CSU cleanroom and the mesa detector structure has been replaced with the thin insulator detector structure to solve the problems encountered during the characterizations. PDMS microfluidic channels and a multichannel measurement system consisting of a probe card, a multiplexing/amplification circuit and a LabVIEW program have been implemented into the LEAC system. In recent years, outbreaks of fast spreading viral diseases, such as bird flu and H1N1, have drawn a lot of concern of the point-of-care virus detection techniques. To test the virus detection ability of LEAC sensor, 40nm and 200nm polystyrene nanoparticles were immobilized onto the waveguide, and the increased scattered light was collected. Sensitivities of 1%/particle and 0.04%/particle were observed for 200nm and 40nm particles respectively.
Open Access
A new algorithm for retrieval of tropospheric wet path delay over inland water bodies and coastal zones using brightness temperature deflection ratios
(Colorado State University. Libraries, 2013) Gilliam, Kyle L., author; Reising, Steven C., advisor; Notaros, Branislav, committee member; Kummerow, Christian, committee member
As part of former and current sea-surface altimetry missions, brightness temperatures measured by nadir-viewing 18-34 GHz microwave radiometers are used to determine apparent path delay due to variations in index of refraction caused by changes in the humidity of the troposphere. This tropospheric wet-path delay can be retrieved from these measurements with sufficient accuracy over open oceans. However, in coastal zones and over inland water the highly variable radiometric emission from land surfaces at microwave frequencies has prevented accurate retrieval of wet-path delay using conventional algorithms. To extend wet path delay corrections into the coastal zone (within 25 km of land) and to inland water bodies, a new method is proposed to correct for tropospheric wet-path delay by using higher-frequency radiometer channels from approximately 50-170 GHz to provide sufficiently small fields of view on the surface. A new approach is introduced based on the variability of observations in several millimeter-wave radiometer channels on small spatial scales due to surface emissivity in contrast to the larger-scale variability in atmospheric absorption. The new technique is based on the measurement of deflection ratios among several radiometric bands to estimate the transmissivity of the atmosphere due to water vapor. To this end, the Brightness Temperature Deflection Ratio (BTDR) method is developed starting from a radiative transfer model for a downward-looking microwave radiometer, and is extended to pairs of frequency channels to retrieve the wet path delay. Then a mapping between the wet transmissivity and wet-path delay is performed using atmospheric absorption models. A frequency selection study is presented to determine the suitability of frequency sets for accurate retrieval of tropospheric wet-path delay, and comparisons are made to frequency sets based on currently-available microwave radiometers. Statistical noise analysis results are presented for a number of frequency sets. Additionally, this thesis demonstrates a method of identifying contrasting surface pixels using edge detection algorithms to identify contrasting scenes in brightness temperature images for retrieval with the BTDR method. Finally, retrievals are demonstrated from brightness temperatures measured by Special Sensor Microwave Imager/Sounder (SSMIS) instruments on three satellites for coastal and inland water scenes. For validation, these retrievals are qualitatively compared to independently-derived total precipitable water products from SSMIS, the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) and the Advanced Microwave Sounding Radiometer for Earth Observing System (EOS) (AMSR-E). Finally, a quantitative method for analyzing the data consistency of the retrieval is presented as an estimate of the error in the retrieved wet path delay. From these comparisons, one can see that the BTDR method shows promise for retrieving wet path delays over inland water and coastal regions. Finally, several additional future uses for the algorithm are described.
Open Access
Accurate dimension reduction based polynomial chaos approach for uncertainty quantification of high speed networks
(Colorado State University. Libraries, 2018) Krishna Prasad, Aditi, author; Roy, Sourajeey, advisor; Pezeshki, Ali, committee member; Notaros, Branislav, committee member; Anderson, Charles, committee member
With the continued miniaturization of VLSI technology to sub-45 nm levels, uncertainty in nanoscale manufacturing processes and operating conditions have been found to translate into unpredictable system-level behavior of integrated circuits. As a result, there is a need for contemporary circuit simulation tools/solvers to model the forward propagation of device level uncertainty to the network response. Recently, techniques based on the robust generalized polynomial chaos (PC) theory have been reported for the uncertainty quantification of high-speed circuit, electromagnetic, and electronic packaging problems. The major bottleneck in all PC approaches is that the computational effort required to generate the metamodel scales in a polynomial fashion with the number of random input dimensions. In order to mitigate this poor scalability of conventional PC approaches, in this dissertation, a reduced dimensional PC approach is proposed. This PC approach is based on using a high dimensional model representation (HDMR) to quantify the relative impact of each dimension on the variance of the network response. The reduced dimensional PC approach is further extended to problems with mixed aleatory and epistemic uncertainties. In this mixed PC approach, a parameterized formulation of analysis of variance (ANOVA) is used to identify the statistically significant dimensions and subsequently perform dimension reduction. Mixed problems are however characterized by far greater number of dimensions than purely epistemic or aleatory problems, thus exacerbating the poor scalability of PC expansions. To address this issue, in this dissertation, a novel dimension fusion approach is proposed. This approach fuses the epistemic and aleatory dimensions within the same model parameter into a mixed dimension. The accuracy and efficiency of the proposed approaches are validated through multiple numerical examples.
Open Access
Computational advancements in the D-bar reconstruction method for 2-D electrical impedance tomography
(Colorado State University. Libraries, 2016) Alsaker, Melody, author; Mueller, Jennifer L., advisor; Cheney, Margaret, committee member; Notaros, Branislav, committee member; Pinaud, Olivier, committee member
We study the problem of reconstructing 2-D conductivities from boundary voltage and current density measurements, also known as the electrical impedance tomography (EIT) problem, using the D-bar inversion method, based on the 1996 global uniqueness proof by Adrian Nachman. We focus on the computational implementation and efficiency of the D-bar algorithm, its application to finite-precision practical data in human thoracic imaging, and the quality and spatial resolution of the resulting reconstructions. The main contributions of this work are (1) a parallelized computational implementation of the algorithm which has been shown to run in real-time, thus demonstrating the feasibility of the D-bar method for use in real-time bedside imaging, and (2) a modification of the algorithm to include \emph{a priori} data in the form of approximate organ boundaries and (optionally) conductivity estimates, which we show to be effective in improving spatial resolution in the resulting reconstructions. These computational advancements are tested using both numerically simulated data as well as experimental human and tank data collected using the ACE1 EIT machine at CSU. In this work, we provide details regarding the theoretical background and practical implementation for each advancement, we demonstrate the effectiveness of the algorithm modifications through multiple experiments, and we provide discussion and conclusions based on the results.
Open Access
Consistency in the AMSR-E snow products: groundwork for a coupled snowfall and SWE algorithm
(Colorado State University. Libraries, 2019) Gonzalez, Ryan L., author; Kummerow, Christian, advisor; Liston, Glen, committee member; Chiu, Christine, committee member; Notaros, Branislav, committee member
Snow is an important wintertime property because it is a source of freshwater, regulates land-atmosphere exchanges, and increases the surface albedo of snow-covered regions. Unfortunately, in-situ observations of both snowfall and snow water equivalent (SWE) are globally sparse and point measurements are not representative of the surrounding area, especially in mountainous regions. The total amount of land covered by snow, which is climatologically important, is fairly straightforward to measure using satellite remote sensing. The total SWE is hydrologically more useful, but significantly more difficult to measure. Accurately measuring snowfall and SWE is an important first step toward a better understanding of the impacts snow has for hydrological and climatological purposes. Satellite passive microwave retrievals of snow offer potential due to consistent overpasses and the capability to make measurements during the day, night, and cloudy conditions. However, passive microwave snow retrievals are less mature than precipitation retrievals and have been an ongoing area of research. Exacerbating the problem, communities that remotely sense snowfall and SWE from passive microwave sensors have historically operated independently while the accuracy of the products has suffered because of the physical and radiometric dependency between the two. In this study, we assessed the relationship between the Northern Hemisphere snowfall and SWE products from the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). This assessment provides insight into regimes that can be used as a starting point for future improvements using coupled snowfall and SWE algorithm. SnowModel, a physically-based snow evolution modeling system driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis, was employed to consistently compare snowfall and SWE by accounting for snow evolution. SnowModel has the ability to assimilate observed SWE values to scale the amount of snow that must have fallen to match the observed SWE. Assimilation was performed using AMSR-E, Canadian Meteorological Centre (CMC) Snow Analysis, and Snow Data Assimilation System (SNODAS) SWE to infer the required snowfall for each dataset. Observed AMSR-E snowfall and SWE were then compared to the MERRA-2 snowfall and SnowModel-produced SWE as well as SNODAS and CMC inferred snowfall and observed SWE. Results from the study showed significantly different snowfall and SWE bias patterns observed by AMSR-E. Specifically, snowfall was underestimated nearly globally and SWE had pronounced regions of over and underestimation. Snowfall and SWE biases were found to differ as a function of surface temperature, snow class, and elevation.
Open Access
Design and simulation of the Colorado State University linear accelerator system
(Colorado State University. Libraries, 2014) Edelen, Jonathan Paul, author; Milton, Stephen, advisor; Biedron, Sandra, advisor; Notaros, Branislav, committee member; Johnson, Thomas, committee member
The University of Twente in the Netherlands recently donated a linear accelerator and free-electron laser system to Colorado State University. A detailed model and simulation of the system must be constructed in order to assist the re-commissioning process at CSU. An initial design of the beam-transport system must also be developed. This thesis begins with the basic theory needed to understand the context of the simulations and then works through the accelerator, starting from the point where the beam is generated and continuing through the whole system to the beam dump. Individual components are simulated, their parameters are characterized, and optimal initial settings are found. These individual simulations are then combined into a complete start-to-end simulation of the machine. The start-to-end simulation is then used to demonstrate the expected performance of the machine with the optimal settings. This provides a system design that will be used in the initial buildup of the accelerator, as well as a simulation tool that can be used for future studies (for example, testing of novel components) or for examining the impact of proposed design changes.
Open Access
Design, fabrication, and demonstration of low-mass, low-power, small-volume, direct detection millimeter-wave radiometers at 92 and 130 GHz
(Colorado State University. Libraries, 2012) Albers, Darrin, author; Reising, Steven C., advisor; Kummerow, Christian, committee member; Notaros, Branislav, committee member; Kangaslahti, Pekka, committee member
Advances in future ocean satellite altimetry missions are needed to meet oceanographic and hydrological objectives. These needs include accurately determining the sea surface height (SSH) on spatial scales of 10 km and larger, as well as monitoring the height of the world's inland bodies of water and the flow rate of rivers. The Surface Water and Ocean Topography (SWOT) mission was recommended by the National Research Council's Earth Science Decadal Survey and selected by the National Aeronautics and Space Administration as an accelerated Tier-2 mission to address these needs. Current surface altimetry missions use nadir pointing 18-37 GHz microwave radiometers to correct for errors in SSH due to wet-tropospheric path delay. Using current antennas at these frequencies, oceanic measurements include significant errors within 50 km of coastlines due to varying emissivity and temperature of land. Higher frequencies (90-170 GHz) can provide proportionally smaller footprints for the same antenna size. In turn, this provides improved retrievals of wet-tropospheric path delay near the coasts. This thesis will focus on the design, fabrication, and testing of two direct detection radiometers with internal calibration at center frequencies of 92 and 130 GHz. Component design, testing and integration of the radiometers using multi-chip modules are discussed. The performance of these radiometers is characterized, including noise figure, internal calibration and long-term stability. These performance parameters, along with their mass, volume, and power consumption, will be used as the basis for the development of future airborne and space-borne millimeter-wave direct detection radiometers with internal calibration.
Open Access
Design, fabrication, and testing of a data acquisition and control system for an internally-calibrated wide-band microwave airborne radiometer
(Colorado State University. Libraries, 2014) Nelson, Scott P., author; Reising, Steven C., advisor; Notaros, Branislav, committee member; Kummerow, Christian, committee member
The National Aeronautics and Space Administration (NASA)'s Earth Science Technology Office (ESTO) administers the Instrument Incubator Program (IIP), providing periodic opportunities to develop laboratory, ground-based and airborne instruments to reduce the risk, cost and schedule of future Earth Science missions. The IIP-10 project proposed in 2010 and led by PI S. Reising at Colorado State University focuses on the development of an internally-calibrated, wide-band airborne radiometer to reduce risks associated with wet-path delay correction for the Surface Water and Ocean Topography (SWOT) mission. This airborne radiometer includes microwave channels at 18.7, 23.8, and 34.0 GHz at both H and V polarizations; millimeter-wave window channels at 90.0, 130.0, 168.0 GHz; and temperature and water vapor sounding channels near 118 and 183 GHz, respectively. These microwave, millimeter-wave window and millimeter-wave sounding channels consist of 6, 3 and 16 channels, respectively, for a total of 25 channels in this airborne instrument. Since the instrument is a prototype for space flight, a great deal of effort has been devoted to minimizing the mass, size and power consumption of the radiometer's front-end. Similar goals of minimizing the mass, size and power consumption have driven the design of the radiometer back-end, which performs the data acquisition and control functions for the entire instrument. The signals output from all 25 radiometer channels are conditioned, integrated and digitized on the analog back-end boards. The radiometer system is controlled by a Field Programmable Gate Array (FPGA) and a buffer board. Each analog back-end board conditions and simultaneously samples four signals, performing analog-to-digital conversion. The digital back-end consists of the buffer board and FPGA, which control and accept data from all seven analog back-end boards required to sample all 25 radiometer channels. The digital back-end also controls the radiometer front-end calibration (also called "Dicke") switching and the motor used to perform cross-track scanning and black body target calibration of the airborne radiometer instrument. The design, fabrication, and test results of the data acquisition and control system are discussed in depth. First, a system analysis determines general requirements for the airborne radiometer back-end. In the context of these requirements, the design and function of each component are described, as well as its relationship to the other components in the radiometer back-end. The hardware and software developed as part of this radiometer back-end are described. Finally, the back-end testing and results of these tests are discussed.
Open Access
Design, optimziation and fabrication of an integrated optoelectronic sensing chip with applications in groundwater contaminant detection and biosensing
(Colorado State University. Libraries, 2014) Erickson, Timothy, author; Lear, Kevin L., advisor; Roberts, Jacob, committee member; Notaros, Branislav, committee member; Collins, George, committee member
The LEAC (Local Evanescent Array Coupled) chip is a CMOS-compatible, waveguide-based, label-free, optoelectronic sensor, which can function as a biosensor or environmental sensor. Unique among optoelectronic sensors, the ~1 cm2 LEAC chip features an integrated photodetector array, which increases device portability, enables multi-analyte detection on a single waveguide, and simplifies system instrumentation. At its core, the LEAC chip is simply a precision refractometer, which can sense very small changes in refractive index (~5x10-6) in its multiple upper cladding sensing regions. The chip can be functionalized for detection of biomarkers or groundwater contaminants, which bind or diffuse into the waveguide's upper cladding sensing region, thereby producing a measurable change in refractive index. The research conducted during my doctoral studies has addressed two important goals. The first was to optimize the chip's sensing performance. The second goal was to run proof of concept experiments, in order to demonstrate its utility in practical sensing applications. By incorporating multiple engineering improvements, the sensing performance of the LEAC chip has been improved to the point where it may be competitive with low-end surface plasmon resonance (SPR) systems for bulk refractive index sensing. We have demonstrated the LEAC sensing platform for both environmental and biosensing applications. These include sensing aromatic hydrocarbons such as benzene, toluene and xylenes in groundwater at sub-ppm concentrations and detection of the cardiac infarction biomarker TroponinI. Research results have been communicated in peer-reviewed journals and presented at conferences, as summarized in Appendix J. Additionally, the intellectual property that was developed during the course of research activities has served as the basis for several patent filings. This dissertation provides a comprehensive account of research conducted on the LEAC sensing platform, while working as a graduate student in Dr. Kevin Lear's laboratory. It is structured in the following manner. In Chapter 1, the basic functionality of LEAC chip is introduced, while providing the necessary background to motivate its development. Chapter 2 provides a comprehensive and comparative overview of other label-free biosensors and groundwater aromatic hydrocarbon contaminant sensors. It reviews the requirements of other sensing systems and demonstrates the uniquely portable aspects of LEAC chip technology. It is provided for completeness, in order to summarize the state-of-the-art in the field of portable sensing and highlight some of the unique advantages of the LEAC sensor. In Chapter 3, the engineering aspects of performance optimization over prior art are described in detail. Whereas the 1st generation LEAC chip was fabricated at Avago Technologies, all 2nd generation LEAC chips have been fabricated by myself in the CSU cleanroom or at the Colorado Nanofabrication Lab in Boulder. The development of 2nd generation LEAC chips, including device physics, modeling, and fabrication is rigorously described. In Chapter 4, the bulk refractive index sensing capabilities of the chip are demonstrated as well as the chip's capacity to perform multi-analyte dry sensing assays . Through design improvements, it is quantitatively shown that the 2nd generation chip is over two orders of magnitude more sensitive than the 1st generation chip. In Chapter 5, the environmental sensing capabilities of the LEAC chip are presented. Teflon AF is first characterized as a unique film for sensing BTX (benzene, toluene, and xylene) contaminants in water using near-IR surface plasmon resonance. Then LEAC chips functionalized with Teflon AF are demonstrated for BTX sensing in water at sub-ppm concentrations. Interference from potential matrix interfering contaminants is evaluated. In Chapter 6, the biosensing capabilities of the LEAC chip are discussed. The LEAC chip is validated for detection of Troponin I. In Chapter 7, areas for future improvements to the LEAC sensing platform are briefly touched upon along with concluding remarks. A number of appendices related to very specific technical aspects of my work have been included as helpful documentation. These appendices include fabrication process flows, the data acquisition system, transimpedance amplifier design, grating coupler designs, mask designs (including testing structures), and other protocols. A list of publications and conferences is provided at the end of this report in Appendix I.
Open Access
Development and fabrication of low-mass, low-power, internally-calibrated, MMIC-based millimeter-wave radiometers at 92 and 166 GHz
(Colorado State University. Libraries, 2012) Lee, Alexander L., author; Reising, Steven C., advisor; Notaros, Branislav, committee member; Kummerow, Christian D., committee member; Kangaslahti, Pekka, committee member
This thesis discusses the design, fabrication, and testing of two millimeter-wave internally calibrated MMIC based radiometers operating at 92 and 166 GHz. These laboratory prototype radiometers are intended to increase the technological maturity of the radiometer components and reduce the risk, development time and cost of deploying satellite based radiometers operating in the 90-170 GHz frequency range. Specifically, radiometers at similar frequencies are being considered on NASA's SWOT mission, planned for launch in 2020. The SWOT mission is an ocean altimetry mission intended to increase the Earth science community's knowledge of the kinetic energy in ocean circulation and mesoscale eddies as well as the vertical transport of heat and carbon in the ocean. These direct detection Dicke radiometers have two internal calibration sources integrated in the front end. These sources consist of a high excess noise ratio noise diode and a temperature controlled matched load. Internal calibration is a requirement on ocean altimetry missions to avoid the need for moving parts, which are necessary to accomplish external calibration. The index of refraction of the atmosphere depends on temperature and humidity. The variability of humidity in time and space is more difficult to measure and model than that of temperature. Changes in the index of refraction of the atmosphere add error to satellite based ocean altimetry measurements. Microwave radiometers have been used on altimetry missions to measure the amount of atmospheric water vapor, and this data is used to correct the altimetry measurements. Traditionally, microwave radiometers in the 18-37 GHz range have been used on these missions. However, due to the large instantaneous fields of view (IFOV) on the Earth's surface, land begins to encroach upon the radiometer's surface footprint at about 40 km from the coast. The emission from the land adds additional error to the radiometer measurements. The amount of error is unknown due to the highly variable emissivity of land. The addition of higher frequency millimeter-wave radiometers in the 90-170 GHz frequency range will reduce the IFOV on the Earth's surface and therefore enable atmospheric water vapor measurements closer to the coasts. The radiometers presented in this thesis are laboratory prototypes. They are intended to demonstrate new component technology and improve estimates of mass, volume, power consumption, and radiometric performance for future space-borne millimeter-wave radiometers.
Open Access
Development of internally-calibrated, direct detection millimeter-wave radiometers to improve remote sensing of wet tropospheric path delay
(Colorado State University. Libraries, 2015) Hadel, Victoria D., author; Reising, Steven C., advisor; Kangaslahti, Pekka, committee member; Notaros, Branislav, committee member; Van Den Heever, Susan, committee member
Satellite ocean altimeters measure the sea surface height by emitting a radar pulse and measuring the time for it to propagate to the surface, bounce off and return to the satellite. Assuming speed-of-light propagation, the sea surface height can be determined. However, water vapor in the atmosphere, which is highly variable both temporally and spatially, reduces the propagation speed of these radar signals, in turn increasing the round-trip radar propagation time, leading to substantial errors in the sea surface height estimation. This delay in the arrival time of radar pulse returns is referred to as wet-tropospheric path delay. Past and current satellite ocean altimeters include nadir-viewing, co-located 18-34 GHz microwave radiometers to measure wet-tropospheric path delay with a precision of 1 cm. However, due to the large antenna footprint sizes at these frequencies, the accuracy of wet path retrievals is substantially degraded within 40 km of coastlines, and retrievals are not provided over land. Because footprint diameter is directly proportional to wavelength for the same antenna aperture size, a viable approach to improve their capability is to add wide-band millimeter-wave window channels in the 90-175 GHz band, thereby achieving finer spatial resolution for a fixed antenna size. To address this need, an internally-calibrated, wide-band, cross-track scanning airborne microwave and millimeter-wave radiometer has been collaboratively developed between Colorado State University (CSU) and Caltech/NASA's Jet Propulsion Laboratory (JPL). This airborne radiometer, referred to as the High Frequency Airborne Microwave and Millimeter Wave Radiometer (HAMMR) includes microwave channels at 18.7, 23.8, and 34.0 GHz at both Quasi-H and Quasi-V polarizations, millimeter-wave window channels at 90, 130, and 168 GHz, as well as temperature and water vapor sounding channels near the 118 and 183 GHz absorption lines, respectively. Since this instrument also serves as a prototype for potential future Earth science missions, substantial effort has been devoted to minimizing the mass, size and power consumption of the radiometer. Preliminary airborne measurements of the HAMMR demonstrate the reliable and robust operation of the millimeter-wave window and sounding channels on an airborne platform, as well as the improvement in spatial resolution that they provide, over that of the traditional microwave channels.
Open Access
Efficient multidimensional uncertainty quantification of high speed circuits using advanced polynomial chaos approaches
(Colorado State University. Libraries, 2016) Ahadi Dolatsara, Majid, author; Roy, Sourajeet, advisor; Notaros, Branislav, committee member; Anderson, Chuck, committee member; Pezeshki, Ali, committee member
With the scaling of VLSI technology to sub-45 nm levels, uncertainty in the nanoscale manufacturing processes and operating conditions have been found to result in unpredictable circuit behavior at the chip, package, and board levels of modern integrated microsystems. Hence, modeling the forward propagation of uncertainty from the device-level parameters to the system-level response of high-speed circuits and systems forms a crucial requirement of modern computer-aided design (CAD) tools. This thesis presents novel approaches based on the generalized polynomial chaos (gPC) theory for the efficient multidimensional uncertainty quantification of general distributed and lumped high-speed circuit networks. The key feature of this work is the development of approaches which are more efficient and/or accurate comparing to recently suggested uncertainty quantification approaches in the literature. Main contributions of this thesis are development of two individual approaches for improvement of the conventional linear regression uncertainty quantification approach, and development of a sparse polynomial expansion of the stochastic response in an uncertain system. The validity of this work is established through multiple numerical examples.
Open Access
Electronic scan weather radar: scan strategy and signal processing for volume targets
(Colorado State University. Libraries, 2013) Nguyen, Cuong Manh, author; Chandra, Chandrasekar V., advisor; Jayasumana, Anura P., committee member; Mielke, Paul W., committee member; Notaros, Branislav, committee member
Following the success of the WSR-88D network, considerable effort has been directed toward searching for options for the next generation of weather radar technology. With its superior capability for rapidly scanning the atmosphere, electronically scanned phased array radar (PAR) is a potential candidate. A network of such radars has been recommended for consideration by the National Academies Committee on Weather Radar Technology beyond NEXRAD. While conventional weather radar uses a rotating parabolic antenna to form and direct the beam, a phased array radar superimposes outputs from an array of many similar radiating elements to yield a beam that is scanned electronically. An adaptive scan strategy and advanced signal designs and processing concepts are developed in this work to use PAR effectively for weather observation. An adaptive scan strategy for weather targets is developed based on the space-time variability of the storm under observation. Quickly evolving regions are scanned more often and spatial sampling resolution is matched to spatial scale. A model that includes the interaction between space and time is used to extract spatial and temporal scales of the medium and to define scanning regions. The temporal scale constrains the radar revisit time while the measurement accuracy controls the dwell time. These conditions are employed in a task scheduler that works on a ray-by-ray basis and is designed to balance task priority and radar resources. The scheduler algorithm also includes an optimization procedure for minimizing radar scan time. In this research, a signal model for polarimetric phased array weather radar (PAWR) is presented and analyzed. The electronic scan mechanism creates a complex coupling of horizontal and vertical polarizations that produce the bias in the polarimetric variables retrieval. Methods for bias correction for simultaneous and alternating transmission modes are proposed. It is shown that the bias can be effectively removed; however, data quality degradation occurs at far off boresight directions. The effective range for the bias correction methods is suggested by using radar simulation. The pulsing scheme used in PAWR requires a new ground clutter filtering method. The filter is designed to work with a signal covariance matrix in the time domain. The matrix size is set to match the data block size. The filter's design helps overcome limitations of spectral filtering methods and make efficient use of reducing ground clutter width in PAWR. Therefore, it works on modes with few samples. Additionally, the filter can be directly extended for staggered PRT waveforms. Filter implementation for polarimetric retrieval is also successfully developed and tested for simultaneous and alternating staggered PRT. The performance of these methods is discussed in detail. It is important to achieve high sensitivity for PAWR. The use of low-power solid state transmitters to keep costs down requires pulse compression technique. Wide-band pulse compression filters will partly reduce the system sensitivity performance. A system for sensitivity enhancement (SES) for pulse compression weather radar is developed to mitigate this issue. SES uses a dual-waveform transmission scheme and an adaptive pulse compression filter that is based on the self-consistency between signals of the two waveforms. Using SES, the system sensitivity can be improved by 8 to 10 dB.
Open Access
Microphysical retrieval and profile classification for GPM dual-frequency precipitation radar and ground validation
(Colorado State University. Libraries, 2013) Le, Minda, author; Chandrasekar, V. Chandra, advisor; Jayasumana, Anura P., committee member; Mielke, Paul W., committee member; Notaros, Branislav, committee member
The Global Precipitation Measurement (GPM) mission, planned as the next satellite mission following the Tropical Rainfall Measurement Mission (TRMM), is jointly sponsored by the National Aeronautic and Space Administration (NASA) of USA and the Japanese Aerospace Exploration Agency (JAXA) with additional partners, the Centre National d'Études Spatiales (CNES), the Indian Space Research Organization (ISRO), the National Oceanic and Atmospheric Administration (NOAA), the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), and others. The core satellite of GPM mission will be equipped with a dual-frequency precipitation radar (DPR) operating at Ku- (13.6 GHz) and Ka- (35.5 GHz) band with the capability to cover ±65° latitude of the earth. One primary goal of the DPR is to improve accuracy in estimation of drop size distribution (DSD) parameters of precipitation particles. The estimation of the DSD parameters helps achieve more accurate estimation of precipitation rates. The DSD is also centrally important in the determination of the electromagnetic scattering properties of precipitation media. The combination of data from the two frequency channels, in principle, can provide more accurate estimates of DSD parameters than the TRMM Precipitation radar (TRMM PR) with Ku- band channel only. In this research, a methodology is developed to retrieve DSD parameters for GPM-DPR. Profile classification is a critical module in the microphysical retrieval system for GPM-DPR. The nature of microphysical models and equations for use in the DSD retrieval algorithm are determined by the precipitation type of each profile and the phase state of the hydrometeors. In the GPM era, the Ka- band channel enables the detection of light rain or snowfall in the mid- and high- latitudes compared to the TRMM PR (Ku- band only). GPM-DPR offers dual-frequency observations (measured reflectivity at Ku- band:Ζm (Ku) and measured reflectivity at Ka- band:Ζm (Ku)) along each vertical profile, which provide additional information for investigating the microphysical properties using the difference in measured radar reflectivities at the two frequencies, a quantity often called the measured dual-frequency ratio (DFRm) can be defined (DFRm=Ζm (Ku) — Ζm (Ka)). Both non-Rayleigh scattering effects and attenuation difference control the shape of the DFRm profile. Its pattern is determined by the forward and backscattering properties of the mixed phase and rain media and the backscattering properties of ice. Therefore, DFRm could provide better performance in precipitation type classification and hydrometeor profile characterization than TRMM PR. In this research, two methods, precipitation type classification (PCM) and hydrometeor profile characterization (HPC), are developed to perform profile classification for GPM-DPR using the DFRm profile and its range variability. The methods have been implemented into the GPM-DPR day one algorithm. Ground validation is an integral part of all satellite precipitation missions. Similar to TRMM, the GPM validation falls into the general class of validation and integration of information from space-borne observing platforms with a variety of ground-based measurements. Dual polarization ground radar is a powerful tool that can be used to address a number of important questions that arise in the validation process, especially those associated with precipitation microphysics and algorithm development. Extensive research has also been done regarding accurate retrievals of rain DSDs as well as attenuation correction for dual-polarization ground radar operating at S-, C- and X- band by using polarimetric measurements. However, polarimetric ground radar operating at a single frequency channel has limitation on DSD retrieval beyond rain region. A dual-frequency and dual-polarization Doppler radar (D3R) operating at the same frequency channels as GPM-DPR has been built. In this research, an algorithm is developed to retrieve DSD parameter for this D3R radar, which will serve as the GPM-DPR ground validation instrument.
Open Access
On modeled and observed warm rainfall occurrence and its relationships with cloud macrophysical properties
(Colorado State University. Libraries, 2014) King, Joshua Matthew, author; Kummerow, Christian, advisor; van den Heever, Susan, advisor; Notaros, Branislav, committee member
Rainfall from low-level, liquid-phase ("warm") clouds over the global oceans is ubiquitous and contributes non-negligibly to the total amount of precipitation that falls to the globe. In this study, modeled and observed warm rainfall occurrence and its bulk statistical relationships with cloud macrophysical properties are analyzed independently and directly compared with one another. Rain is found to fall from ~25% of the warm, maritime clouds observed from space by CloudSat and from ~27% of the warm clouds simulated within a large-scale, fine-resolution radiative convective equilibrium experiment performed with the Regional Atmospheric Modeling System (RAMS). Within both the model and the observations, the fractional occurrence of warm rainfall is found to increase with both column-integrated liquid water mass and cloud geometric depth, two cloud-scale properties that are shown to be directly related to one another. However, warm rain within RAMS is more likely with lower amounts of column water mass than observations indicate, suggesting that the parameterized cloud-to-rain conversion processes within RAMS produce rainfall too efficiently. To gain insight into the relationships between warm rainfall production and the concentration of liquid water within a cloud layer, warm rainfall occurrence is subsequently investigated as a joint, simultaneous function of both cloud depth and column-integrated water mass. While rainfall production within RAMS is largely governed by the availability of liquid water within the cloud volume, rain from observed warm clouds with relatively little column water mass is actually more likely to fall from deeper clouds with lower cloud-mean water contents. The latter, CloudSat-derived trend is shown to be robust across different seasons and environmental conditions; it varies little when the warm cloud distribution is stratified into ascending (day) and descending (night) CloudSat overpass groups. Using temperature differences between RAMS cloud tops and their immediate, surrounding environments as a proxy for cloud-top buoyancy, an attempt is then made to quantitatively investigate simulated warm rain occurrence within the broader context of cloud life cycle. It is found that rainfall likelihoods from RAMS-simulated warm clouds with cloud top temperatures warmer than their surrounding environments more closely resemble the overall CloudSat-derived rainfall occurrence trends. This result suggests that the CloudSat-observed warm cloud distribution is characterized by increased numbers of positively buoyant, developing clouds.
Open Access
Optofluidic intracavity spectroscopy for spatially, temperature, and wavelength dependent refractometry
(Colorado State University. Libraries, 2012) Kindt, Joel D., author; Lear, Kevin L., advisor; Buchanan, Kristen, committee member; Notaros, Branislav, committee member
A microfluidic refractometer was designed based on previous optofluidic intracavity spectroscopy (OFIS) chips utilized to distinguish healthy and cancerous cells. The optofluidic cavity is realized by adding high reflectivity dielectric mirrors to the top and bottom of a microfluidic channel. This creates a plane-plane Fabry-Perot optical cavity in which the resonant wavelengths are highly dependent on the optical path length inside the cavity. Refractometry is a useful method to determine the nature of fluids, including the concentration of a solute in a solvent as well as the temperature of the fluid. Advantages of microfluidic systems are the easy integration with lab-on-chip devices and the need for only small volumes of fluid. The unique abilities of the microfluidic refractometer in this thesis include its spatial, temperature, and wavelength dependence. Spatial dependence of the transmission spectrum is inherent through a spatial filtering process implemented with an optical fiber and microscope objective. A sequence of experimental observations guided the change from using the OFIS chip as a cell discrimination device to a complimentary refractometer. First, it was noted the electrode structure within the microfluidic channel, designed to trap and manipulate biological cells with dielectrophoretic (DEP) forces, caused the resonant wavelengths to blue-shift when the electrodes were energized. This phenomenon is consistent with the negative dn/dT property of water and water-based solutions. Next, it was necessary to develop a method to separate the optical path length into physical path length and refractive index. Air holes were placed near the microfluidic channel to exclusively measure the cavity length with the known refractive index of air. The cavity length was then interpolated across the microfluidic channel, allowing any mechanical changes to be taken into account. After the separation of physical path length and refractive index, it was of interest to characterize the temperature dependent refractive index relationship, n(T), for phosphate buffered saline. Phosphate buffered saline(PBS) is a water-based solution used with our biological cells because it maintains an ion concentration similar to that found in body fluids. The n(T) characterization was performed using a custom-built isothermal apparatus in which the temperature could be controlled. To check for the accuracy of the PBS refractive index measurements, water was also measured and compared with known values in the literature. The literature source of choice has affiliations to NIST and a formulation of refractive index involving temperature and wavelength dependence, two parameters which are necessary for our specialized infrared wavelength range. From the NIST formula, linear approximations were found to be dn/dT = -1.4×10-4 RIU °C-1 and dn/dλ = -1.5×10-5 RIU nm-1 for water. A comparison with the formulated refractive indices of water indicated the measured values were off. This was attributed to the fact that light penetration into the HfO2/SiO2 dielectric mirrors had not been considered. Once accounted for, the refractive indices of water were consistent with the literature, and the values for PBS are believed to be accurate. A further discovery was the refractive index values at the discrete resonant wavelengths were monotonically decreasing, such that the dn/dλ slope for water was considerably close to the NIST formula. Thus, n(T,λ) was characterized for both water and PBS. A refractive index relationship for PBS with spatial, temperature, and wavelength dependence is particularly useful for non-uniform temperature distributions caused by DEP electrodes. First, a maximum temperature can be inferred, which is the desired measurement for cell viability concerns. In addition, a lateral refractive index distribution can be measured to help quantify the gradient index lenses that are formed by the energized electrodes. The non-uniform temperature distribution was also simulated with a finite element analysis software package. This simulated temperature distribution was converted to a refractive index distribution, and focal lengths were calculated for positive and negative gradient index lenses to a smallest possible length of about 10mm.
Open Access
Plasma chemical driven biomedical applications with a radio frequency driven atmospheric pressure plasma jet
(Colorado State University. Libraries, 2012) Choi, Myeong Yeol, author; Collins, George J., advisor; Hendrickson, Dean A., committee member; Notaros, Branislav, committee member; Watanabe, Masahiro, committee member
We present radio frequency driven atmospheric pressure plasma jet for various biomedical applications such as tissue removal, bacterial sterilization, and tooth whitening. Two different types of plasma assisted electrosurgery, remote electrode plasma jet and plasma jet surrounding monopolar electrosurgical electrode, were employed to enhance tissue removal in terms of less heat damage on contiguous tissue and fast removal rate. Chlorine based chemical (CHxClx) additives in argon plasma jet enhanced tissue removal rate, proportional to the Cl radical density in the plasma jet. Pulsed RF provided another knob to control the removal profile, heat damage, and removal rate. Hydrogen peroxide (H2O2) additive provided abundant OH generation in the helium plasma jet. It not only enhanced tissue removal rate but also reduced heat damage on the contiguous tissue. The tissue removal mechanism of helium-H2O2 plasma is explained based on the FTIR measurement of the tissue samples, and optical emission and absorption spectra. Hydrogen peroxide addition to argon plasma jet was employed for bacterial inactivation. Observed OH density by optical emission and absorption was proportional to the number of deactivated microorganism. Argon plasma jet in DI water also provided abundant OH on the interface of water and gas plasma. The OH radicals applied on porcine tooth sample selectively removed the stain without damaging the underlying enamel.
Open Access
Radar multi-sensor (RAMS) quantitative precipitation estimation (QPE)
(Colorado State University. Libraries, 2015) Willie, Delbert Darrell, author; Chandrasekar, V., advisor; Mielke, Paul, committee member; Jayasumana, Anura P., committee member; Notaros, Branislav, committee member
Quantitative precipitation estimation (QPE) continues to be one of the principal objectives for weather researchers and forecasters. The ability of radar to measure over broad spatial areas in short temporal successions encourages its application in the pursuit of accurate rainfall estimation, where radar reflectivity-rainfall (Z-R) relations have been traditionally used to derive quantitative precipitation estimation. The purpose of this research is to present the development of a regional dual polarization QPE process known as the RAdar Multi-Sensor QPE (RAMS QPE). This scheme applies the dual polarization radar rain rate estimation algorithms developed at Colorado State University into an adaptable QPE system. The methodologies used to combine individual radar scans, and then merge them into a mosaic are described. The implementation and evaluation is performed over a domain that occurs over a complex terrain environment, such that local radar coverage is compromised by blockage. This area of interest is concentrated around the Pigeon River Basin near Asheville, NC. In this mountainous locale, beam blockage, beam overshooting, orographic enhancement, and the unique climactic conditions complicate the development of reliable QPE's from radar. The QPE precipitation fields evaluated in this analysis will stem from the dual polarization radar data obtained from the local NWS WSR-88DP radars as well as the NASA NPOL research radar.
Open Access
Reconciling TRMM precipitation estimates related to El Niño Southern Oscillation variability
(Colorado State University. Libraries, 2017) Henderson, David S., author; Kummerow, Christian D., advisor; van den Heever, Susan C., committee member; Rutledge, Steven, committee member; Notaros, Branislav, committee member
Over the tropical oceans, large discrepancies in TRMM passive and active microwave rainfall retrievals become apparent during El Niño-Southern Oscillation (ENSO) events, where TMI retrievals exhibit a systematic shift in precipitation seemingly correlated with ENSO phase, while the PR does not. To investigate the causality of this relationship, this dissertation focuses, both spatially and temporally, on the evolution of precipitation organization between El Niño and La Niña conditions and their impacts on TRMM TMI and PR retrieved precipitation through the use of ground validation (GV) and satellite-based sources. The precipitation validation is performed as a function of convective organization through implementation of defined precipitation regimes, which have physical characteristics consistent across meteorological regimes. Before a full evaluation of TRMM retrieved rain rates is completed, an assessment of TRMM ground validation (GV) oceanic rain rate estimates is necessary. The robustness of radar-based GV rainfall estimates from the Kwajalein S-band KPOL radar are examined through comparisons with the Kwajalein rain gauge network. The TRMM-GV 2A53 rainfall product is found to heavily underestimate convective rain types, where prominent biases occur as precipitation becomes more organized. To further examine these rainfall biases, GV and polarimetrically-tuned rain rates are compared, where GV biases in both the 2A53 product and convective and stratiform Z-R relationships are minimized when the rain rate relationships are developed specifically as a function of precipitation regime. The results demonstrate that exploration into precipitation regimes should be considered when deriving and evaluating rain relationships to establish the source and range of uncertainties existing within different precipitating systems. TRMM radar (PR) and radiometer (TMI) rain rates are then evaluated though multiple case studies of collocated TRMM and KPOL rain rates at the 1°x1° and TMI footprint scale. The results of this study indicate that TRMM TMI and PR rainfall biases are best explained when derived as a function of organization and convective fraction. Large underestimates in both TMI and PR rain rates are associated with predominately convective rainfall across all regimes, where TMI rainfall underestimates both PR and GV rain rates. While PR rain rate estimates typically underestimate GV rainfall, TMI rain rates are heavily overestimated in rainfall regimes containing predominantly stratiform precipitation. Over the Kwajalein region, differences in TMI and PR rain rates seem to be driven by the occurrence of organized precipitation, where TMI-PR differences during El Niño conditions largely derive from MCS-like precipitating systems containing large stratiform precipitating regions. Application of the resultant biases helps mitigate the TMI-PR differences occurring between the ENSO phases and explain uncertainties introduced by the TMI Bayesian retrieval. Expanding the analysis tropics-wide, TRMM discrepancies directly relate to a shift from isolated deep convection during La Niña events toward organized precipitation during El Niño events with the largest variability occurring in the Pacific basins. During El Niño conditions, an increase in stratiform raining fraction leads to an increase in TMI rain rates that is less prevalent in PR rain rate retrievals. Reanalysis and AIRS data indicate that higher occurrences in organized systems are aided by increased mid- and upper-tropospheric moisture accompanied by more frequent deep convection. During La Niña events tropical rainfall is dominated by isolated deep convective regimes associated with drier mid-tropospheric conditions and strong mid- and upper level zonal wind shear. Application of the known TMI and PR biases yields increased consistency in PR rainfall with the radiometer-based TMI and GPCP rainfall estimates. The resultant satellite-based rainfall estimates are in general agreement when describing the response of tropical precipitation to ENSO induced variability in tropical SSTs.
Open Access
Theory and mitigation of electron back-bombardment in thermionic cathode radio frequency guns
(Colorado State University. Libraries, 2015) Edelen, Jonathan Paul, author; Milton, Stephen, advisor; Biedron, Sandra, advisor; Notaros, Branislav, committee member; Johnson, Thomas, committee member
Photocathode RF guns are currently the standard for high- power, low-emittance beam generation in free-electron lasers. These devices require the use of high-power lasers (which are bulky and expensive to operate) and high-quantum-efficiency cathodes (which have limited lifetimes requiring frequent replacement). The use of RF-gated thermionic cathodes enables operation without a large drive laser and with long lifetimes. One major limitation of RF-gated thermionic cathodes is that electrons emitted late in the RF period will not gain enough energy to exit the gun before being accelerated back towards the cathode by the change in sign of the RF field. These electrons deposit their kinetic energy on the cathode surface in the form of heat, limiting the ability to control the output current from the cathode. This dissertation is aimed at understanding the fundamental design factors that drive the back-bombardment process and at exploring novel techniques to reduce its impact on a high-current system. This begins with the development of analytic models that predict the back-bombardment process in single-cell guns. These models are compared with simulation and with a measurement taken at a specific facility. This is followed by the development of analytic models that predict the effects of space-charge on back-bombardment. These models are compared with simulations. This is followed by an analysis of how the addition of multiple cells will impact the back-bombardment process. Finally, a two-frequency gun is studied for its ability to mitigate the back-bombardment process. This dissertation provides new insight on how the back-bombardment process scales as a function of the beam parameters and how space-charge affects this process. Additionally this dissertation shows how a second frequency can be used to mitigate the back-bombardment effect.