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Full-Text Articles in Engineering
Adjustment Of Rapidscat Backscatter Measurements For Improved Radar Images, Garrett Scott Mcdonald
Adjustment Of Rapidscat Backscatter Measurements For Improved Radar Images, Garrett Scott Mcdonald
Theses and Dissertations
RapidScat is a spaceborne wind scatterometer mounted on the International Space Station (ISS). The RapidScat mission lasted from September 2014 to November 2016. RapidScat enables the measurement of diurnal patterns of sigma-0 measurements. This capability is possible because of the non-sun-synchronous orbit of the ISS, in which the local time of day (LTOD) of sigma-0 measurements gradually shifts over time in any given location. The ISS platform is a relatively unstable platform for wind scatterometers. Because of the varying attitude of the ISS, RapidScat experiences a constant variation of its pointing vector. Variations of the pointing vector cause variations in …
Impact Of Antenna Mutual Coupling, Propagation, And Nonreciprocity On Propagation-Based Key Establishment, Attiya Mahmood
Impact Of Antenna Mutual Coupling, Propagation, And Nonreciprocity On Propagation-Based Key Establishment, Attiya Mahmood
Theses and Dissertations
Propagation-based key establishment is a physical layer method for generating encryption keys based on two radios observing a reciprocal propagation channel. This work explores the impact of mutual coupling when communicating nodes are equipped with multiple antennas, multipath richness in the propagation environment, and practical limitations caused by the nonreciprocal nature of RF circuits on key establishment. First, network theory is used to formulate a model of a realistic communication system which incorporates transmit sources and receive loads, impedance matching networks, low-noise amplifiers (LNAs), mutually coupled antenna arrays, and a passive eavesdropper. Afterwards, a detailed analysis is performed to quantify …
Calibration Of Rapidscat Over-Land Σ0, Forrest Dayton Minor
Calibration Of Rapidscat Over-Land Σ0, Forrest Dayton Minor
Theses and Dissertations
RapidScat is a Ku-band radar that measures the normalized backscatter coefficient σ0 of the Earth's surface. Launched in 2015, it currently operates on the International Space Station. Nearly one year into its mission, RapidScat measurements began exhibiting strange behavior that is believed to be caused by a change in receiver gain. Changes in gain are compensated for during post-processing, but the measurements have a lower signal-to-noise ratio (SNR). Calibration and validation of σ0 measurements from this low SNR state are performed using extended land targets with various signal strengths. Study areas include the Amazon rainforest, Congo rainforest, Argentina …
Calibration And Validation Of The Rapidscat Scatterometer Using Natural Land Targets, Nathan Mark Madsen
Calibration And Validation Of The Rapidscat Scatterometer Using Natural Land Targets, Nathan Mark Madsen
Theses and Dissertations
RapidScat is a Ku-band scatterometer that was launched September 2014 and is currently operating on the International Space Station. It estimates ocean vector winds through accurate measurement of the normalized radar coefficient (σ0) of the ocean surface. In order to ensure the accuracy of σ0 measurements and consistency with previous Ku-band scatterometers, post-launch calibration and validation is necessary. Calibration and validation is performed using natural land targets, namely the Amazon and Congo rainforests, to complement calibration efforts over the ocean. The σ0 response of the targets is estimated with respect to viewing angle and time of …
Intercalibration Of Quikscat And Oscat Land Backscatter, John Colin Barrus
Intercalibration Of Quikscat And Oscat Land Backscatter, John Colin Barrus
Theses and Dissertations
The Ku-band SeaWinds-on-QuikSCAT scatterometer (QuikSCAT) operated continuously from 1999 to 2009. Though its primary mission was to estimate global ocean winds, QuikSCAT has proven useful in a variety of geophysical studies using land backscatter measurements. The end of the primary QuikSCAT mission in 2009 has prompted interest for continuing the QuikSCAT land dataset with other scatterometers. The Oceansat-2 scatterometer (OSCAT), launched in 2009, is a viable candidate for continuing the QuikSCAT time series because of the similarities of both sensors in function and design. An important difference in the sensors is that they operate at slightly different incidence angles. Continuing …
Improving Accuracy In Microwave Radiometry Via Probability And Inverse Problem Theory, Derek Lavell Hudson
Improving Accuracy In Microwave Radiometry Via Probability And Inverse Problem Theory, Derek Lavell Hudson
Theses and Dissertations
Three problems at the forefront of microwave radiometry are solved using probability theory and inverse problem formulations which are heavily based in probability theory. Probability theory is able to capture information about random phenomena, while inverse problem theory processes that information. The use of these theories results in more accurate estimates and assessments of estimate error than is possible with previous, non-probabilistic approaches. The benefits of probabilistic approaches are expounded and demonstrated. The first problem to be solved is a derivation of the error that remains after using a method which corrects radiometric measurements for polarization rotation. Yueh [1] proposed …
Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz
Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz
Faculty Publications
The SeaWinds-on-QuikSCAT (QuikSCAT) and SeaWinds-on-ADEOS-2 (SeaWinds) scatterometers measure the normalized radar backscatter (O) of the earth's surface. These identical radar sensors are on different spaceborne platforms in similar orbits. QuikSCAT and SeaWinds data are used to infer near-surface wind vectors, polar sea-ice extent, polar-ice melt events, etc. In order to verify the relative calibration of these sensors, a simple cross calibration based on land backscatter measurements is performed. A first-order polynomial model is used to remove the incidence angle dependence of O for selected regions of the Amazon rainforest and the Sahara Desert. It is shown that the two sensors …
Frequency Estimation Of Linear Fm Scatterometer Pulses Received By The Seawinds Calibration Ground Station, Spencer S. Haycock
Frequency Estimation Of Linear Fm Scatterometer Pulses Received By The Seawinds Calibration Ground Station, Spencer S. Haycock
Theses and Dissertations
The SeaWinds Calibration Ground Station (CGS) is a passive ground station used to receive and sample transmissions from the SeaWinds scatterometer. During post processing, the received transmissions are characterized in order to verify proper instrument operation and to eliminate error in satellite telemetry and in data products generated from processing SeaWinds data. Sources of instrument error include uncertainties in transmitted power, pulse timing, and carrier frequency drift. Identifying these errors prevents their propagation to data products. A key aspect of this analysis involves accurately estimating the parameters of the SeaWinds transmissions. As better parameter estimates are researched and developed, the …
A New Method For Melt Detection On Antarctic Ice-Shelves And Scatterometer Calibration Verification, Lukas Brad Kunz
A New Method For Melt Detection On Antarctic Ice-Shelves And Scatterometer Calibration Verification, Lukas Brad Kunz
Theses and Dissertations
Ku-band dual-polarization radar backscatter measurements from the SeaWinds on QuikScat scatterometer and microwave radiometer measurements from the Special Sensor Microwave/Imager (SSM/I) are used to determine periods of surface melt and freeze in the Antarctic ice-shelves. The normalized radar backscatter (sigma-0) and backscatter polarization ratio (PR) are used in the maximum likelihood estimation of the ice-state. This method is used to infer the daily ice-surface conditions for 25 selected study points located on the Ronne, Ross, Larsen, Fimbul, Amery, and Shackleton Ice-shelves. The temporal and spatial variations of the radar response are also observed for various neighborhood sizes surrounding each given …
Dynamic Element Matching Techniques For Delta-Sigma Adcs With Large Internal Quantizers, Brent C. Nordick
Dynamic Element Matching Techniques For Delta-Sigma Adcs With Large Internal Quantizers, Brent C. Nordick
Theses and Dissertations
This thesis presents two methods that enable high internal quantizer resolution in delta-sigma analog-to-digital converters. Increasing the quantizer resolution in a delta-sigma modulator can increase SNR, improve stability and reduce integrator power consumption. However, each added bit of quantizer resolution also causes an exponential increase in the power dissipation, required area and complexity of the dynamic element matching (DEM) circuit required to attenuate digital-to-analog converter (DAC) mismatch errors. One way to overcome these drawbacks is to segment the feedback signal, creating a "coarse" signal and a "fine" signal. This reduces the DEM circuit complexity, power dissipation, and size. However, it …
Satellite Scatterometers: Calibration Using A Ground Station And Statistical Measurement Theory, Peter Kenneth Yoho
Satellite Scatterometers: Calibration Using A Ground Station And Statistical Measurement Theory, Peter Kenneth Yoho
Theses and Dissertations
Satellite scatterometers have recently gained popularity due to their unique ability to measure global geophysical data on a daily basis. Increased interest in scatterometry mandates improved design and calibration of these instruments. This dissertation presents new techniques for scatterometer calibration and addresses issues related to the design of future instruments and applications. First, the use of a calibration ground station is considered. A new methodology is established for calibration of SeaWinds, NASA's current scatterometer, using a receive-only ground station. Principles of the methodology are implemented, new analysis techniques developed, and important results obtained for instrument timing, frequency, power, position, and …
Postlaunch Sensor Verification And Calibration Of The Nasa Scatterometer, David G. Long, Wu-Yang Tsai, James E. Graf, Carroll Winn, James N. Huddleston, R. Scott Dunbar, Michael H. Freilich, Frank J. Wentz, W. Linwood Jones
Postlaunch Sensor Verification And Calibration Of The Nasa Scatterometer, David G. Long, Wu-Yang Tsai, James E. Graf, Carroll Winn, James N. Huddleston, R. Scott Dunbar, Michael H. Freilich, Frank J. Wentz, W. Linwood Jones
Faculty Publications
Scatterometer instruments are active microwave sensors that transmit a series of microwave pulses and measure the returned echo power to determine the normalized radar backscattering cross section (sigma-0) of the ocean surface from which the speed and direction of near-surface ocean winds are derived. The NASA Scatterometer (NSCAT) was launched on board the ADEOS spacecraft in August 1996 and returned ten months of high-quality data before the failure of the ADEOS spacecraft terminated the data stream in June 1997. The purpose of this paper is to provide an overview of the NSCAT instrument and sigma-0 computation and to describe the …
Calibration Of Spaceborne Scatterometers Using Tropical Rain Forests, David G. Long, Gary B. Skouson
Calibration Of Spaceborne Scatterometers Using Tropical Rain Forests, David G. Long, Gary B. Skouson
Faculty Publications
Wind scatterometers are radar systems designed specifically to measure the normalized radar backscatter coefficient (O) of the ocean's surface in order to determine the near-surface wind vector. Postlaunch calibration of a wind scatterometer can be performed with an extended-area natural target such as the Amazon tropical rain forest. Rain forests exhibit a remarkably high degree of homogeneity in their radar response over a very large area though some spatial and temporal variability exist. The authors present a simple technique for calibrating scatterometer data using tropical rain forests, Using a polynomial model for the rolloff of O with incidence angle, the …