Physics Commons^™

The Feasibility Of Data Whitening To Improve Performance Of Weather Radar, A. C. Koivunen, Alexander Kostinski

Department of Physics Publications

The problem of efficient processing of correlated weather radar echoes off precipitation is considered. An approach based on signal whitening was recently proposed that has the potential to significantly improve power estimation at a fixed pulse repetition rate/scan rate, or to allow higher scan rates at a given level of accuracy. However, the previous work has been mostly theoretical and subject to the following restrictions: 1) the autocorrelation function (ACF) of the process must be known precisely and 2) infinite signal-to-noise ratio is assumed. Here a computational feasibility study of the whitening algorithm when the ACF is estimated and in …

Non-Rayleigh Signal Statistics In Clustered Statistically Homogeneous Rain, A. R. Jameson, Alexander Kostinski

Department of Physics Publications

As the sample volume of a remote sensing instrument moves through sufficiently variable conditions, recent work shows that the amplitudes and associated intensities can deviate significantly at times from expectations based on Rayleigh signal statistics because fluctuations in the number of scatterers leads to a doubly stochastic measurement process. While non-Rayleigh deviations yield average biases for both logarithmic and linear detectors, perhaps of greater importance is the enhancement of the variance of the bias distribution for square law detectors. In this work the authors explore the potential existence of non-Rayleigh effects even in the statistically homogeneous rain when fluctuations in …

Fluctuation Properties Of Precipitation. Part Iv: Finescale Clustering Of Drops In Variable Rain, A. R. Jameson, Alexander Kostinski, A Kruger

Department of Physics Publications

In recent studies it is shown that in variable rain the spatial distribution of drops is not Poissonian. However, these past studies were limited to 1-min drop counts, which likely correspond to spatial scales of a few hundred to several hundreds of meters.

In this work results based on 1-s drop counts using a video disdrometer are reported. It is shown that the clustering of raindrops previously found during intervals of 1 min also occurs during 1 s as well in convective rain. These latter temporal scales likely correspond to spatial features having dimensions from only a few to tens …

The Texture Of Clouds, A. R. Jameson, Alexander Kostinski, R A. Black

Department of Physics Publications

Using a precise definition of clustering, it is shown that in two tropical cumulus clouds, droplets appear to be bunched over distances ranging from at least a kilometer or more down to several centimeters. A statistical framework is proposed for quantifying clustering in terms of a Poisson probability mixture. While these observations require further substantiation in many different clouds, droplet clustering may play a role in diverse phenomena from the coalescence growth of raindrops to the scattering of radiation by clouds.

Fluctuation Properties Of Precipitation. Part Ii: Reconsideration Of The Meaning And Measurement Of Raindrop Size Distributions, A. R. Jameson, Alexander Kostinski

Department of Physics Publications

For M drop size categories, rain is frequently viewed simply as the superposition of M,statistically independent Poisson-distributed drop fluxes each described by its own mean concentration. Implicit in such a Poissonian model is the assumption of uncorrelated counts among the drops. However, it is well known that drop size distributions are the result of the processes of collision, coalescence, and breakup, which should lead to correlations.

This inconsistency is resolved in this work. Using 1-min disdrometer measurements, two-point cross-correlation functions are used to show that drop counts at different sizes are correlated rather than independent. Moreover, it is argued …

Fluctuation Properties Of Precipitation. Part I: On Deviations Of Single-Size Drop Counts From The Poisson Distribution, Alexander Kostinski, A. R. Jameson

Department of Physics Publications

The traditional statistical description of the spatial and temporal distributions of cloud droplets and raindrops is the Poisson process, which tends to place the drops as uniformly as randomness allows. Yet, the “clumpy” nature of clouds and precipitation is apparent to most casual observers and well known to cloud physicists. Is such clumpiness consistent with the Poisson statistics? The authors explore the possibility of deviations from the Poisson distribution using temporal raindrop counting experiments. Disdrometer measurements during the passage of a squall line strongly indicate that a mixture of Poisson distributions (Poisson mixture) provides a better description of the frequency …

Roughening And Preroughening Of Diamond-Cubic {111} Surfaces, Donald L. Woodraska, John A. Jaszczak

Department of Physics Publications

A solid-on-solid model for {111} surfaces of diamond-cubic materials that correctly takes into account the diamond-cubic crystal structure has been developed for Monte Carlo simulation. In addition to a roughening transition at temperature T_R, a distinct preroughening transition at T_PR≈0.43T_R is indicated by divergences in the surface specific heat and order-parameter susceptibility. Preroughening appears to arise naturally in our nearest-neighbor bond model from the entropic freedom available in the nontrivial crystal structure. Preroughening is shown to dramatically lower the nucleation barrier for growth and etching at low driving forces.

Non-Rayleigh Signal Statistics Caused By Relative Motion During Measurements, A. R. Jameson, Alexander Kostinski

Department of Physics Publications

In order to reduce fluctuations, remote sensing devices such as radars and radiometers typically sample many times before forming an estimate. When mean values are stationary during this sampling period, the fluctuations in the amplitudes and intensities obey the same probability density functions (pdf) as those for each sample contributing to the estimate. However, it is shown in this work that when mean values change from sample to sample (i.e., pulse to pulse for most radars), the pdf's of the amplitudes and intensities differ from those corresponding to the samples. Such changes can be inherent to the scatterers as, for …

Simulation Of Slow Variable-Angle Spinning Nmr Spectra. Application To 13c Bonded To N, B H. Suits, J. Sepa, David Wnite

Michigan Tech Publications, Part 1

Simulations of NMR spectra for spin-j nuclei in rigid solids spun at relatively slow speeds and at angles other than the magic angle are presented. Particular emphasis is on the case where I3C is bonded to a quadrupolar nucleus such as 14N. The feasibility of quantitatively extracting the chemical-shift tensor, bond lengths through the dipolar interaction, and the electric-field gradient of the neighboring nucleus from a single (1-D) spectrum is demonstrated. The sensitivity of the observed changes in the spectra to changes in the physical and experimental parameters is discussed and illustrated using nitrile I3C spectra of solid CH3CN. Equations …

The Use Of Optimal Polarizations For Studying The Microphysics Of Precipitation: Nonattenuating Wavelengths, John Kwiatkowski, Alexander Kostinski, A. R. Jameson

Department of Physics Publications

The objective of this work is to explore relationships between the microphysical properties of precipitation and optimal polarizations. The dependence of three optimal polarization parameters (asymmetry ratio 𝒜, optimal tilt τ_op, and optimal ellipticity ϵ_op,) on the reflectivity-weighted mean drop shape, mean canting angle, and standard deviation of a Gaussian canting angle distribution is studied. This is accomplished by using computer simulations that provide the rms scattering matrix for an ensemble of canted drops with a prescribed two-parameter canting angle distribution. Also examined are the effects of propagation on the polarization parameters for nonattenuating wavelengths.

The …

A Random Wave Method For Detecting Phase Imbalance In A Coherent Radar Receiver, Zhenni Wang, Alexander Kostinski

Department of Physics Publications

The question of monitoring the angle between the in-phase (I) and quadrature (Q) channels of a coherent radar receiver is considered in this paper. Random interference-type scattering (e.g., rain echo) is assumed so that the received signal is a random phasor sum. It is also assumed that I and Q voltages have a (90 + ϕ₀) phase difference. The effects of nonzero phase imbalance ϕ₀ on the I and Q statistics are examined. Joint I and Q as well as amplitude and phase probability distributions are derived. It is shown that the cross-correlation …

Spaceborne Radar Sensing Of Precipitation Above An Ocean Surface: Polarization Contrast Study, Alexander Kostinski, John Kwiatkowski, A. R. Jameson

Department of Physics Publications

This feasibility study explores the potential benefits of polarization adjustment for spaceborne radar sensing of precipitation. More specifically, the role of the wave polarization in separating or “distinguishing” ocean surface return from the hydrometeor echoes of a “chirped” signal is examined.

To that end, experimental as well as computational data for the polarization scattering matrices of hydrometeors and ocean surfaces are obtained and used to calculate ocean and precipitation “response” to the transmitted pulse for various rain rates and incidence angles. The analysis is restricted to X and C bands, but simulations are performed for several signal-to-noise ratios, rain rates, …