Morton Kanefsky

Detection of weak signals with polarity coincidence arrays

Polarity Coincidence Array detectors (PCA) are considered for testing the hypothesis that a random signal is common to an array of receivers which contain noise processes that are independent representations of a given class of stochastic processes. A standard procedure is to reduce the received data by sampling and then hard limiting. Hard limiting is shown to introduce an inherent loss in input signal power of 1.96 dB when the input data is a sequence of independent samples from a stationary Gaussian process. However, when the stationary and/or Gaussian assumptions are violated, the relative efficiencies of the PCA detectors can greatly improve. When the input samples are dependent, it is necessary to assume Ganssian inputs in order to analyze the PCA detectors. However, these devices are still unaffected by a nonstationary noise level that is slowly varying relative to the inverse bandwidth of the pre-filter. Furthermore, the loss due to clipping is considerably reduced as the sample dependence (i.e., sampling rate) increases. For rapid sampling rates, the spectral shapes of the inputs must be known accurately in order to fix the false-alarm rate at some pre-assigned value.

Numerical study of transient stimulated Brillouin scattering

Seeded, transient, stimulated Brillouin scattering (SBS) is studied using a new noniterative, numerical algorithm to solve this two‐point boundary value problem. The coupled pump, Stokes, and phonon equations are solved numerically, including the effects of pump depletion and a finite phonon lifetime. The noniterative approach leads to efficient computation (<30 s of cpu time, VAX 8000 series computer for 500 by 5000 points in space and time, respectively). The numerical study predicts transient oscillations in the pump and the Stokes intensities. The frequency of these oscillations depends on the phonon lifetime and the depleted, exponential SBS gain. This work is the first known prediction of these oscillations.

On 2-D recursive LMS algorithms using ARMA prediction for ADPCM encoding of images

A two-dimensional (2D) linear predictor which has an autoregressive moving average (ARMA) representation well as a bias term is adapted for adaptive differential pulse code modulation (ADPCM) encoding of nonnegative images. The predictor coefficients are updated by using a 2D recursive LMS (TRLMS) algorithm. A constraint on optimum values for the convergence factors and an updating algorithm based on the constraint are developed. The coefficient updating algorithm can be modified with a stability control factor. This realization can operate in real time and in the spatial domain. A comparison of three different types of predictors is made for real images. ARMA predictors show improved performance relative to an AR algorithm.

On adaptive nonparametric detection systems using dependent samples

A procedure is obtained for modifying given sampled-data parametric detectors to make them asymptotically nonparametric. Unlike standard nonparametric devices, these detectors do not require the assumption of independent samples but only a knowledge of the input spectral shapes. As examples of this technique, two types of conventional array detectors are modified to produce nonparametric systems.

Limits to the efficiency of beam combination by stimulated Brillouin scattering

The probability distribution function of the phase difference between two thermal-noise-initiated stimulated Brillouin scattering beams was calculated and measured as a function of the correlation between the noise sources. This correlation is determined by the spatial overlap of the two pump beams. Perfect phase locking of every pair of Brillouin-scattered pulses is shown to be impossible.

Predictive source coding techniques using maximum likelihood prediction for compression of digitized images

A predictive compression technique is examined, using maximum likelihood prediction of the image pixel based on the Markov mesh model, that encodes the differences via Gordon block-bit-plane (GBBP) encoding. The procedure is very efficient in that it requires a bit rate near the entropy of the source. For images with many quantization levels, maximum likelihood prediction can be cumbersome to implement. Thus, a suboptimal procedure called differential bit-plane coding (DBPC) is investigated. This is easily implemented, even for a large number of quantization levels, and is reasonably efficient.

A reduced edge distortion median filtering algorithm for binary images

Abstract The repeated application of a median filtering algorithm is an effective tool for smoothing images, i.e., filtering additive random and impulsive noises, while preserving edge information. A certain degree of distortion, however, is introduced by such a filter. In images that can be modeled as objects in a homogeneous background, such distortion occurs mostly on object boundaries and generally depends on the type of algorithm (standard, regular recursive, modified recursive, etc.) used to implement the median filter. While these distortions are statistically similar, the question arises as to whether there exist other implementations of a repeated median filter which achieve the same degree of smoothing but consistently yield less edge distortion. In this paper we show the existence of one such implementation for binary images. Using a test image, we demonstrate that our algorithm yields an output image which is significantly closer to the original image than the outputs of the repeated standard or regular recursive algorithms. The performance of our algorithm combines the smoothing capability of a repeated median filter which uses the same window, and the edge preserving property of one which uses a smaller window.

A statistical description of stimulated Brillouin scattering beam combination efficiency

The mutual coherence between two stimulated Brillouin signals produced by undepleted pump beams that are partially overlapped is studied. The mutual coherence of the stimulated-Brillouin-scattered beams determines the efficiency with which the two beams can be combined. The statistical properties of the mutual coherence are calculated. The mechanism for coupling of two stimulated-Brillouin-scattering outputs is four-wave mixing. Mutual coherence is found to depend on the pump beams pulse duration, the mediums phonon lifetime, and the degree of overlap between the laser pump beams. >

Beam coupling, stimulated Brillouin scattering, and four-wave mixing.

Measurements of the probability density function of the mutual coherence of two stimulated-Brillouin-scattered Stokes outputs are reported. The variation of the probability density function with the polarization, relative intensities, and overlap of the pumping laser beams demonstrates that the coupling between the Stokes outputs is due to four-wave mixing.

Recursive two-dimensional median filtering algorithms for fast image root extraction

The authors develop and evaluate two new two-dimensional fast recursive median filtering algorithms, for image root extraction. The first recursive algorithm, which is called the fast binary root algorithm, converges to a root of a binary image in one pass including a number of local rescans. The second is referred to as the fast multilevel root algorithm. It converges to a root of a multilevel image in two passes, the second of which includes a number of local rescans. The number of ordering positions required by the authors algorithms is shown to be significantly less than those required by the standard and regular recursive median filters. >