Phase Coherence Function Research Articles

Wavelet analysis methods in the comprehensive study approach of skin microhemodynamics as a cardiovascular unit

Adaptive wavelet transform techniques for studying of microcirculatory blood flow oscillations are described. It is shown that the suggested methods will be especially claimed in the analysis of low-frequency components of short-lived transient processes under various functional test conditions. In addition, the use of adaptive wavelet transform reduces the essential duration of signal registration, which can be useful in the study of the microhemodynamics in patients with heavy pathologies. Also the method for investigating the phase relationships between microvasculatory oscillations is given which based on estimating the values of wavelet phase coherence function. The proposed method makes it possible to identify frequency intervals with high and low phase correlations of peripheral blood flow oscillations.

A very fast phase inversion approach for small baseline style interferogram stacks

The recently developed interferometric time-series analysis techniques have shown great potential in ground surface deformation monitoring applications. Such techniques overcome the drawbacks of the traditional differential radar interferometry (DInSAR) and can achieve millimeter-level measurement accuracy. One of the most important operations in interferometric time-series analysis techniques — referred to as phase inversion — is to estimate relative deformation velocity and digital elevation model error from a double-differenced interferometric phase time-series. Unfortunately, current phase inversion methods generally exhibit a low computational efficiency due to their high non-linearity, especially in the case when the dimension of an interferogram stack is large. In this paper, a new approach is proposed to efficiently resolve phase inversion problems defined on stacks constructed by interferograms with small baselines. The approach separates an estimation procedure into two parts. First, preliminary estimates are obtained by weighted least squares. Then, the estimates are refined by optimizing the corresponding ensemble phase coherence function. The proposed approach was applied to simulated and real data. Experimental results demonstrate that it can accurately address the phase inversion problem with a very high computational performance.

Comparison of simultaneous line-of-sight signals at 9.6 and 34.5 GHz

Signals at 9.6 and 34.52 GHz, propagated simultaneously over a slant line-of-sight overwater path, have been analyzed to compare the power spectra of phase-of-arrival variations and fading and to determine the coherence of these signals with regard to both phase variations and fading. The phase data at the two radio frequencies exhibited nearly identical power spectra from 0.01 to 5 Hz and very high coherence from 0.01 to 0.1 Hz. The coherence dropped rapidly above 0.1 Hz and was in most cases less than 0.4 above 0.5 Hz. The power spectra of fading were similar in shape at the two frequencies, but the fading spectral density was consistently higher at 34.52 GHz than at 9.6 GHz from 0.1 to 5 Hz. The shape of the coherence function for fading was similar to that of the corresponding phase coherence function, but the fading coherence was lower at the low spectral frequencies. The possible effect of the small spatial separation of the propagation path on the coherence analysis is discussed.

Directivity of a Linear Array in a Random Transmission Medium

A simple derivation is given of the phase autocorrelation function of a monochromatic signal during transmission through a medium with random fluctuations of refractive index. The resulting phase coherence function is then applied to the theory of the linear array antenna to yield a formula for the degraded directivity pattern. The analysis developed here was conceived primarily with reference to acoustic signals and sonar ranging systems, although it may be applied, mutatis mutandis, to a wider variety of acoustic and even electromagnetic problems. For concreteness, however, we shall employ a vocabulary appropriate to the case of sonar signals and antennas. The problem to be considered is the following: Given a source of monochromatic radiation situated far enough from the receiving antenna to be considered a point source, what will be the response, as a function of bearing angle, of a linear array antenna to the signal if the transmission medium has small random irregularities of its refractive index?