Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Electrical and Computer Engineering

Brigham Young University

1999

Articles 1 - 8 of 8

Full-Text Articles in Engineering

Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant Nov 1999

Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant

Faculty Publications

A wind scatterometer makes measurements of the normalized radar-backscatter coefficient O of the ocean surface. To retrieve the wind, a geophysical model function (GMF), which relates O to the near-surface wind, is used. The wind vector can be estimated using maximum-likelihood techniques from several O measurements made at different azimuth angles. The probability density of the measured O is assumed to be Gaussian with a variance that depends on the true O and therefore, depends on the wind through the GMF. With this model for wind estimation, the Cramer-Rao (C-R) bound is derived for wind estimation, and its implications for …

Go to article

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 May 1999

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 …

Go to article

Cryosphere Applications Of Nscat Data, David G. Long, Mark R. Drinkwater May 1999

Cryosphere Applications Of Nscat Data, David G. Long, Mark R. Drinkwater

Faculty Publications

Though designed to measure vector winds over the ocean, new imaging techniques facilitate the use of NASA scatterometer data (NSCAT) in cryosphere studies. NSCAT provides data of unprecedented coverage, resolution, and quality which, when coupled with the scatterometer image reconstruction with filtering (SIRF) algorithm, enables images of O at resolutions approaching 8 km over stationary targets. Such images are useful in ice mapping and classification, and multidecadal studies are possible by comparison with Seasat Scatterometer (SASS) data. The utility of NSCAT data in polar ice studies is illustrated through a review of two cryosphere applications of NSCAT data: (1) sea-ice …

Go to article

Stratified Volume Diffractive Optical Elements As High Efficiency Gratings, Gregory P. Nordin, D. M. Chambers May 1999

Stratified Volume Diffractive Optical Elements As High Efficiency Gratings, Gregory P. Nordin, D. M. Chambers

Faculty Publications

We propose stratified volume diffractive optical elements as a new type of diffractive optical element that is capable of functioning as a high-efficiency grating in applications with requirements not suited to traditional holographic or diffractive optical techniques. In this approach, diffractive optical fabrication methods are used to construct an optical structure that emulates volume grating behavior. We discuss the diffraction properties of stratified volume diffractive optical elements and compare them with those used previously in both volume holographic optical elements and stratified volume holographic optical elements. A systematic design process is then presented for deriving structure parameters. We illustrate this …

Go to article

The Probability Density Of Spectral Estimates Based On Modified Periodogram Averages, David G. Long, Paul E. Johnson May 1999

The Probability Density Of Spectral Estimates Based On Modified Periodogram Averages, David G. Long, Paul E. Johnson

Faculty Publications

Welch's (1967) method for spectral estimation of averaging modified periodograms has been widely used for decades. Because such an estimate relies on random data, the estimate is also a random variable with some probability density function. Here, the PDF of a power estimate is derived for an estimate based on an arbitrary number of frequency bins, overlapping data segments, amount of overlap, and type of data window, given a correlated Gaussian input sequence. The PDFs of several cases are plotted and found to be distinctly non-Gaussian (the asymptotic result of averaging frequency bins and/or data segments), using the Kullback-Leibler distance …

Go to article

The Probability Distribution Of Nscat Measurements, Paul E. Johnson, David G. Long Mar 1999

The Probability Distribution Of Nscat Measurements, Paul E. Johnson, David G. Long

Faculty Publications

NSCAT makes only indirect measurements of wind. The direct measurement is of the backscattered radar power. The signal power is contaminated by radiometric noise so a separate measurement of the noise power is subtracted from the signal-plus-noise measurement to estimate the backscattered power. Using the radar equation, sigma-0 is computed from the measured signal power. From multiple sigma-0 mesaurements made at different azimuth angles, the wind is estimated. In wind retrieval, the NSCAT sigma-0 measurements are assumed to have a Gaussian probability distribution with a variance which depends on the mean. Given this distribution model, the maximum-likelihood estimtor is formed …

Go to article

Micropolarizer Array For Infrared Imaging Polarimetry, M. W. Jones, Gregory P. Nordin, P. C. Deguzman, J. T. Meier Jan 1999

Micropolarizer Array For Infrared Imaging Polarimetry, M. W. Jones, Gregory P. Nordin, P. C. Deguzman, J. T. Meier

Faculty Publications

The design and fabrication of a micropolarizer array for imaging polarimetry is described for the 3–5-μm-wavelength region. Each micropolarizer consists of a 475-nm-period Mo wire grid in a 16 μm × 16 μm aperture. Interference lithography is used to generate the small grating features through an etch mask layer. Arrays of 256 × 256 micropolarizers at three distinct angular orientations have been fabricated that permit the measurement of the first three Stokes vector components in each pixel of an imaging polarimeter. An imaging system composed of a micropolarizer array integrated directly onto a focal plane array has been assembled, and …

Go to article

A Cloud-Removal Algorithm For Ssm/I Data, David G. Long, Douglas L. Daum, Quinn P. Remund Jan 1999

A Cloud-Removal Algorithm For Ssm/I Data, David G. Long, Douglas L. Daum, Quinn P. Remund

Faculty Publications

Microwave radiometers, while traditionally utilized in atmospheric and oceanic studies, can also be used in land surface applications. However, the problem of undesirable atmospheric effects caused by clouds and precipitation must be addressed. In this paper, temporal composite surface brightness images are generated from special sensor microwave/imager (SSM/I) data with the aid of new algorithms to eliminate small-scale distortion caused by clouds or precipitation. Mean, second-highest value, modified maximum average (MMA), and hybrid compositing algorithms are compared. The effectiveness of each algorithm is illustrated through simulation and real data distribution analysis. The results show that the second-highest value algorithm is …

Go to article