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IEEE International Symposium on Geoscience and remote sensing (IGARSS)

作者： J.S. Lee D.L. Schuler R.H. Lang K.J. Ranson Remote Sensing Division Naval Research Laboratory Inc. Washington D.C. DC USA Department of Electrical Engineering and Computer Science George Washington University Washington D.C. DC USA Biospheric Sciences Branch NASA Goddard Space Flight Center Greenbelt MD USA

A K-distribution has been developed to characterize the statistical properties of multi-look processed polarimetric SAR data. The probability density function (PDF) was derived as the product of a gamma distributed random variable and the polarimetric covariance matrix. The latter characterizes the speckle and the former depicts the inhomogeneity (texture). For multi-look data incoherently averaged from correlated one-look samples, the authors found that, for better modeling, the number of looks has to assume a non-integer value. A procedure was developed to estimate the equivalent number of looks and the parameter of the K-distribution. Experimental results using NASA/JPL 4-look and 16-1ook polarimetric SAR data substantiated this multi-look K-distribution. The authors also found that the multi-look process reduced the inhomogeneity and made the K-distribution less significant.< >

关键词： Spatial resolution Radar scattering Covariance matrix Speckle Rayleigh scattering Random variables Statistical distributions Radar polarimetry Histograms remote sensing

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SWEPT FREQUENCY REFLECTOMETER DESIGN FOR IN-SITU PERMITTIVITY MEASUREMENTS

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IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 1993年第3期42卷 730-734页

作者： PLUMB, RG MA, H Radar Systems and Remote Sensing Laboratory Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA Fenni National Accelerator Laboratory Batavia IL USA Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA

A prototype, broad-band vector reflectometer for in-situ field measurements of permittivity is presented. The system was designed primarily to measure permittivity of sea ice in the 2-18 GHz frequency range but works equally well on other materials. The reflectometer design is based upon FMCW radar concepts. In the design, a linear frequency-modulated waveform is generated, and a portion of it is coupled off and passed through a delay line to serve as the local oscillator for the incident and reflected channels which receive most of the generated waveform. The reflectometer measures the complex reflection coefficient of a probe, a short monopole antenna mount-ed on a circular ground plane, attached to the reflectometer input. Permittivity is obtained by constructing a normalized input impedance of the probe. The input impedance of the probe is measured in two media, a standard medium such as air, and the medium under test. The impedance measured in the standard medium is used to construct a fourth-order rational function for the normalized input impedance. The normalized impedance is used with the measured impedance in the medium under test to obtain the permittivity. Finally, measured permittivity data for air, 1-Butanol, and Teflon are presented.

关键词： Permittivity measurement Sea measurements Antenna measurements Probes Impedance measurement Prototypes Vectors Frequency measurement Sea ice Radar

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Root-loci for periodic linear systems 25

Root-loci for periodic linear systems

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25th Southeastern Symposium on System Theory, SSST 1993

作者： Zhu, J. Vemula, S.K. Louisiana State Univ. Electrical and Computer Engineering Department Baton RougeLA70803 United States Louisiana State Univ. Remote Sensing Aind Image Processing Laboratory Baton RougeLA70803 United States

ISBN: (纸本)0818635606

According to the Floquet theory, an nth-order linear periodic (LP) system of the form yn+αn(t) y/sup n-1/+...+α2(t)dy(t)/dt+α1(t)y=0 can be transformed into an equivalent linear time-invariant (LTI) system whose characteristic roots, known as Floquet characteristic exponents (FCEs), determine the stability of the LP system. A technique for obtaining an approximation of the characteristic equation for the FCEs is developed. Parametric loci of the FCE, similar to the root locus plot for a LTI system, are then developed for the LP system. The technique is exemplified by 2nd-order LP systems. The FCE loci are useful in the stability analysis and control design for LP systems. © 1993 IEEE.

关键词： Root loci

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A new adaptive image contrast enhancement method

A new adaptive image contrast enhancement method

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image and Video processing 1993

作者： Yu, Tian-Hu Mitra, S.K. Department of Electrical and Computer Engineering Signal and Image Processing Laboratory University of California Santa BarbaraCA93106 United States

In direct methods of contrast enhancement, a contrast measure is first defined, which is then modified by a mapping function to generate the pixel value of the enhanced image. Various mapping functions such as the square root function, the exponential function, etc., have been introduced for the contrast measure modification. However, these functions do not produce satisfactory contrast enhancement results and are usually sensitive to noise and digitization effects. In addition, they are computationally complex from the point of view of implementation. In this paper, we propose a simple polynomial mapping function for the contrast measure modification. The polynomial function is easy to implement on digital computers and provides very satisfactary contrast enhancement. We also introduce an adaptive clipping technique to control the dynamic range of the output image. © 1993 SPIE. All rights reserved.

关键词： Exponential functions

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A New Method for Evaluating Floquet Characteristic Exponents of Periodic Linear Systems

A New Method for Evaluating Floquet Characteristic Exponents...

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American Control Conference (ACC)

作者： J. Zhu S. K. Vemula Electrical and Computer Engineering Department Remote Sensing and Image Processing Laboratory Louisiana State University Baton Rouge LA USA Electrical and Computer Engineering Department Louisiana State University Baton Rouge LA USA

It is well-known that the stability of linear periodic (LP) systems can be assessed using Floquet Characteristic Exponents (FCE). In this paper, a new method is presented for evaluating FCE for nth-order scalar periodic linear systems based on a recently developed unified eigenvalue theory for linear time-varying (LTV) Systems [1]. The new theory allows FCEs to be evaluated from the DC term of the Fourier series of periodic PD-eigen-values of a LP system. Comparing to the well-known Monodromy Matrix (MM) method and Infinite Dimensional Determinant (IDD) method for evaluating FCE 1 the solutions obtained by the new method have rapid local convergence. This new method also allow stability boundaries in the parameter space of a LP system to be evaluated and plotted directly. The new results shed some light OL the general stability assessment problem for vector periodic linear systems and aperiodic LTV systems. Further studies along this direction are also discussed in this paper.

关键词： Linear systems Eigenvalues and eigenfunctions Vectors Fourier series Frequency Equations Stability analysis remote sensing image processing Laboratories

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Histogram-shape preserving algorithm for image enhancement

Histogram-shape preserving algorithm for image enhancement

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IEEE International Symposium on Circuits and Systems (ISCAS)

作者： T.-H. Yu S.K. Mitra Department of Electrical and Computer Engineering Signal and Image Processing Laboratory University of California Santa Barbara CA USA

A new direct contrast enhancement algorithm is proposed. It can be used to enhance the contrast of an image without increasing the dynamic range of the pixel values. A distinctive property of the proposed method is that it yields results matching the characteristic of the human visual system. The histogram of the enhanced image has almost the same shape as that of the original image.< >

关键词： image enhancement Dynamic range Pixel Histograms Shape Humans Visual system Displays Computational complexity Signal processing

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Determination of ocean environmental parameters from a Ka-band scatterometer

Determination of ocean environmental parameters from a Ka-ba...

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OCEANS

作者： C. Evans S. Haimov R.K. Moore V. Hesany Radar Systems and Remote Sensing Laboratory Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA

A 3-beam Ka-band radar was used as a vector slope gauge with scale like that of a pitch-and-roll buoy. The direction of dominant wave travel, the variance in wave slopes, and the directional spectra of waves are discussed. The slope distribution of ocean waves at this scale is nearly normal, and thus the authors used the moments of a bivariate normal distribution to fit an ellipse to the wave slopes. The orientation of the major axis of the ellipse indicates the direction of dominant wave travel, with 180/spl deg/ ambiguity. In addition, statistics of the slope distribution are readily obtainable from the fitted ellipse. The wave-direction ambiguity is then resolved by fitting an ellipse to the directional histogram of the slope distribution using the least-square method. Due to the asymmetry of the waves, the center of the ellipse is shifted from the origin in the direction from which the dominant waves are traveling. The authors' method of calculating wave slopes and determining the direction of waves is then compared with the standard method used with pitch-and-roll buoys. The authors then compare these with those obtained by F. Ziemer of GKSS, Geesthacht, Germany.< >

关键词： Radar measurements Radar antennas Sea measurements Gaussian distribution Antenna measurements Fluid flow measurement Sea surface Radar remote sensing Ocean waves Histograms

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Optimum detection of Weibull-distributed targets

Optimum detection of Weibull-distributed targets

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OCEANS

作者： M. Rose S. Haimov R.K. Moore Radar Systems and Remote Sensing Laboratory Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA

The backscattered power from an ocean-observing radar usually contains large, randomly spaced excursions often called sea spikes. These spikes can be considered as fluctuating targets embedded in a fluctuating background. The power returned from the fluctuating targets can be modeled as having a Weibull probability density function. The power from the fluctuating background can be modeled as an exponential probability density function. The authors examine a simple scheme for detection of the fluctuating targets in the single-hit case using a fixed-threshold detector. The detection threshold is calculated via the maximum a posteriori decision rule.< >

关键词： Oceans Radar detection Sea surface Radar remote sensing Spaceborne radar Probability density function Detectors Radar scattering Rayleigh scattering Clutter

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Nonlinear filters for image sharpening and smoothing

Nonlinear filters for image sharpening and smoothing

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IEEE International Conference on Systems engineering

作者： Mitra Yu Signal and Image Processing Laboratory Department of Electrical & Computer Engineering University of California Santa Barbara CA USA

A general approach to the transform-magnitude-shaping-based image enhancement method is advanced. In the method, the magnitude of the input image transform is modified using a nonlinear mapping expressible as a power series, while its phase is kept invariant. The inverse transform of the modified image transform results in a sharpening or smoothing depending on the choice of the power series coefficients. Further improvement in the overall enhancement is achieved by a two-channel processing scheme which is implemented by applying different transform amplitude shaping methods to the low-frequency and high-frequency components. Examples the proposed enhancement method are included.< >

关键词： Filtering image processing Transforms

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Slope and hydrodynamic modulation of radar scatter from the sea

Slope and hydrodynamic modulation of radar scatter from the ...

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OCEANS

作者： V. Hesany R.K. Moore S. Haimov Radar Systems and Remote Sensing Laboratory Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA

Microwave backscatter from the ocean surface is largely due to Bragg scattering from short surface ripples. Modulation of the signal results from changes in the local angle of incidence as the local slope changes, and from variations in Bragg ripple amplitude. The slope (tilt) modulation can be modeled as a memoryless nonlinear system. The hydrodynamic modulation results from a nonuniform distribution of the amplitude of the small-scale ripples over the large-scale waves. For azimuthally traveling waves the hydrodynamic modulation dominates, while for waves propagating in other directions, both tilt and hydrodynamic modulation are significant. The authors developed a 35-GHz radar vector slope gauge (VSG) to measure the orthogonal components of the surface slopes within the radar footprint. Simultaneous measurements of the surface slope and radar cross section permit determination of the relative contribution of slope and hydrodynamic modulations to the overall fluctuation of the radar signal. The authors present a method for separating effects due to the surface tilting from hydrodynamic effects. They include a sample result based on this approach with data from the SAXON-FPN experiment in November, 1990.< >

关键词： Radar scattering Hydrodynamics Sea surface Radar cross section Radar measurements Amplitude modulation Sea measurements Backscatter Oceans Nonlinear systems

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