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Browsing by Author "Reising, Steven C., advisor"

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    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.
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    ItemOpen 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.
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    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.
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    ItemOpen 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.
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    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.
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    Development, fabrication and testing of the scanning and calibration subsystems for the Tropospheric Water and Cloud ICE instrument for 6U CubeSats
    (Colorado State University. Libraries, 2019) Kilmer, Braxton, author; Reising, Steven C., advisor; Chandrasekar, V., committee member; Chiu, Christine, committee member
    Global observations of ice cloud particle size and ice water content are needed to improve weather forecasting and climate prediction. The interaction between ice particles and upwelling radiation at sub-millimeter-wavelengths strongly depends on ice particle size and observation frequency. Sub-millimeter-wavelength radiometry provides the capability to fill an observational gap by allowing the detection and sizing of ice particles with diameters between 50 μm and 1 mm. Atmospheric temperature and water vapor profiles can also be yielded at sub-millimeter-wavelengths. The Tropospheric Water and Cloud ICE (TWICE) millimeter- and sub-millimeter-wave radiometer instrument is currently under development for 6U CubeSats in a joint effort among Colorado State University (lead), NASA/Caltech Jet Propulsion Laboratory, and Northrop Grumman Corporation. The TWICE radiometer instrument is designed to provide global measurements of cloud ice, as well as temperature and water vapor profiles in the upper troposphere/lower stratosphere. The TWICE radiometer instrument has 16 frequency channels near 118 GHz for temperature profiling, near 183 and 380 GHz for water vapor profiling, and centered on 240, 310, 670, and 850 GHz quasi-window channels for ice particle sizing. The TWICE radiometer instrument uses a conical scanning strategy to observe the Earth's atmosphere and surface. The complete TWICE scan is designed to sweep out a 200° arc once per second, and the scan direction reverses every second interval. The TWICE scanning system is designed to fit inside a 6U CubeSat in terms of volume and mass, while meeting the torque and acceleration requirements of the scanning radiometer instrument. A stepper motor and gearbox mechanism were selected for the TWICE scanning system. Precisely placed position sensors, in combination with stepper motor step calculation, provide sufficient angular position data, in place of a traditional encoder. The TWICE scanning system has been tested, and angular position analysis has been performed. The TWICE instrument performs end-to-end, two-point radiometric calibration by observing an ambient temperature calibration target and cosmic microwave background reflector during each conical scan. The ambient calibration target is designed to enable simultaneous blackbody measurements at all TWICE millimeter- and sub-millimeter-wave channels. Calibration target design parameters, including size, geometry, thermal and electromagnetic properties, have been chosen to meet the performance requirements of the ambient target and to minimize temperature gradients. Reflection coefficient measurements have been performed in the millimeter to sub-millimeter wavelength range of the TWICE channels. Thermal analysis of the ambient calibration target has been performed using ANSYS software. The resulting ambient calibration target design meets functional requirements as well as size and weight constraints to fit into a 6U CubeSat. The TWICE radiometer instrument employs several subsystems that need to communicate during nominal operation. An interface board was designed to meet the communication needs of and provide power regulation for the various interfacing subsystems of the instrument. The interface board is responsible for controlling the scanning subsystem of the radiometer instrument, performing temperature data acquisition for the radiometer instrument front end and the ambient calibration target, routing signals to and from the control and data handling subsystem of the radiometer instrument, and regulating power to the on-board computer. The interface board has been manufactured and its performance has been tested.
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    Effects of background winds and temperature on bores, strong wind shears and concentric gravity waves in the mesopause region
    (Colorado State University. Libraries, 2009) Yue, Jia, author; She, Chiao-Yao, advisor; Reising, Steven C., advisor
    Using data from the CSU sodium lidar and Kyoto University OH airglow imager at Fort Collins, CO, this thesis provides a comprehensive, though qualitative, understanding for three different yet related observed fluid-dynamical phenomena in the mesopause region. The first project involves the convection-excited gravity waves observed in the OH airglow layer at 87 km. Case study on May 11, 2004 is discussed in detail along with statistical studies and a ray-tracing modeling. A single convection source matches the center of the concentric gravity waves. The horizontal wavelengths and periods of these gravity waves were measured as functions of both radius and time. The weak mean background wind between the lower and middle atmosphere determines the penetration of the gravity waves into higher altitude. The second project involves mesospheric bores observed by the same OH imager. The observation on October 9, 2007 suggests that when a large-amplitude gravity wave is trapped in a thermal duct, its wave front could steepen and forms bore-like structure in the mesopause. In turn, the large gravity wave and its bore may significantly impact the background. Statistical study reveals the possible link between the jet/front system in the lower atmosphere and the large-scale gravity waves and associated bores in the mesopause region. The third project involves the relationship between large wind shear generation and sustainment and convective/dynamic stabilities measured by the sodium lidar at the altitude of 80-105 km during 2002-2005. The correlation between wind shear, S, and Brunt-Vaisala frequency, N suggests that the maximum sustainable wind shear is determined by the necessary condition for dynamic instability of Richardson number, leading to the result that the maximal wind shear occurs at altitudes of lower thermosphere where the atmosphere is convectively very stable. The dominate source for sustainable large windshears appears to be the semidiurnal tidal-period perturbations with shorter vertical wavelengths and greater amplitude.
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    Increasing vertical resolution of three-dimensional atmospheric water vapor retrievals using a network of scanning compact microwave radiometers
    (Colorado State University. Libraries, 2011) Sahoo, Swaroop, author; Reising, Steven C., advisor; Bringi, V. N., 1949-, committee member; Krueger, David A., committee member
    The thermodynamic properties of the troposphere, in particular water vapor content and temperature, change in response to physical mechanisms, including frictional drag, evaporation, transpiration, heat transfer and flow modification due to terrain. The planetary boundary layer (PBL) is characterized by a high rate of change in its thermodynamic state on time scales of typically less than one hour. Large horizontal gradients in vertical wind speed and steep vertical gradients in water vapor and temperature in the PBL are associated with high-impact weather. Observation of these gradients in the PBL with high vertical resolution and accuracy is important for improvement of weather prediction. Satellite remote sensing in the visible, infrared and microwave provide qualitative and quantitative measurements of many atmospheric properties, including cloud cover, precipitation, liquid water content and precipitable water vapor in the upper troposphere. However, the ability to characterize the thermodynamic properties of the PBL is limited by the confounding factors of ground emission in microwave channels and of cloud cover in visible and IR channels. Ground-based microwave radiometers are routinely used to measure thermodynamic profiles. The vertical resolution of such profiles retrieved from radiometric brightness temperatures depends on the number and choice of frequency channels, the scanning strategy and the accuracy of brightness temperature measurements. In the standard technique, which uses brightness temperatures from vertically pointing radiometers, the vertical resolution of the retrieved water vapor profile is similar to or larger than the altitude at which retrievals are performed. This study focuses on the improvement of the vertical resolution of water vapor retrievals by including scanning measurements at a variety of elevation angles. Elevation angle scanning increases the path length of the atmospheric emission, thus improving the signal-to-noise ratio. This thesis also discusses Colorado State University's (CSU) participation in the European Space Agency (ESA)'s "Mitigation of Electromagnetic Transmission errors induced by Atmospheric WAter Vapor Effects" (METAWAVE) experiment conducted in the fall of 2008. CSU deployed a ground-based network of three Compact Microwave Radiometers for Humidity profiling (CMR-Hs) in Rome to measure atmospheric brightness temperatures. These measurements were used to retrieve high-resolution 3-D atmospheric water vapor and its variation with time. High-resolution information about water vapor can be crucial for the mitigation of wet tropospheric path delay variations that limit the quality of Interferometric Synthetic Aperture Radar satellite interferograms. Three-dimensional water vapor retrieval makes use of radiative transfer theory, algebraic tomographic reconstruction and Bayesian optimal estimation coupled with Kalman filtering. In addition, spatial interpolation (kriging) is used to retrieve water vapor density at unsampled locations. 3-D humidity retrievals from Rome data with vertical and horizontal resolution of 0.5 km are presented. The water vapor retrieved from CMR-H measurements is compared with MM5 Mesoscale Model output, as well as with measurements from the Medium Resolution Imaging Spectrometer (MERIS) aboard ESA's ENVISAT and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Aqua and Terra satellites.
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    Integration, characterization, and calibration of the high-frequency airborne microwave and millimeter-wave radiometer (HAMMR) instrument
    (Colorado State University. Libraries, 2014) Johnson, Thaddeus, author; Reising, Steven C., advisor; Morton, Yu, committee member; Vonder Haar, Thomas H., committee member; Kangaslahti, Pekka, committee member
    Current satellite ocean altimeters include nadir-viewing, co-located 18-34 GHz microwave radiometers to measure wet-tropospheric path delay. 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. A viable approach to improve their capability is to add wide-band millimeter-wave window channels in the 90-183 GHz band, thereby achieving finer spatial resolution for a fixed antenna size. In this context, the upcoming Surface Water and Ocean Topography (SWOT) mission is in formulation and planned for launch in late 2020 to improve satellite altimetry to meet the science needs of both oceanography and hydrology and to transition satellite altimetry from the open ocean into the coastal zone and over inland water. To address wet-path delay in these regions, the addition of 90-183 GHz millimeter-wave window-channel radiometers to current Jason-class 18-34 GHz radiometers, is expected to improve retrievals of wet-tropospheric delay in coastal areas and to enhance the potential for over-land retrievals. To this end, an internally-calibrated, wide-band, cross-track scanning airborne microwave and millimeter-wave radiometer is being developed in collaboration between Colorado State University (CSU) and Caltech/NASA's Jet Propulsion Laboratory (JPL). 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, 130, 168 GHz; and temperature and water vapor sounding channels adjacent to the 118 and 183 GHz absorption lines, respectively. Since this instrument is demonstrating this technology for the potential use in future Earth science missions, substantial effort has been put into ensuring the instrument has a minimal mass and volume and is robust and well characterized. To this end the optical alignment has been extensively tested and characterized and a novel blackbody calibration target has been designed and integrated into the system. All supporting sub-systems such as power distribution and data acquisition have been integrated into the chassis allowing the instrument to be easily run by a single operator. Preliminary test flights have been done that demonstrate the reliability and robustness of this instrument as well as demonstrating the increased special resolution of the millimeter-wave window and sounding channels over that of the Jason-class 18-34 GHz radiometers.
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    Millimeter and sub-millimeter wave radiometers for atmospheric remote sensing from CubeSat platforms
    (Colorado State University. Libraries, 2018) Ogut, Mehmet, author; Reising, Steven C., advisor; Chandrasekar, V., committee member; Kummerow, Christian, committee member; Vivekanandan, Jothiram, committee member
    To view the abstract, please see the full text of the document.
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    Retrieval techniques and information content analysis to improve remote sensing of atmospheric water vapor, liquid water and temperature from ground-based microwave radiometer measurements
    (Colorado State University. Libraries, 2015) Sahoo, Swaroop, author; Reising, Steven C., advisor; Notaros, Branislav M., committee member; Vivekanandan, Jothiram, committee member; Rutledge, Steven A., committee member
    To view the abstract, please see the full text of the document.