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Browsing by Author "Kangaslahti, Pekka, committee member"

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    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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    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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    ItemOpen 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.
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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.