Physics Commons^™

Direct Observations Of Coherent Backscatter Of Radar Waves In Precipitation, A. R. Jameson, A. B. Kostinski

Department of Physics Publications

In previous work, it was argued that a source of radar coherent scatter occurs in the direction perpendicular to the direction of wave propagation because of the presence of grids of enhanced particle concentrations with spatial periodicities in resonance with the radar wavelength. While convincing, the evidence thus far has been indirect. In this work the authors now present direct observations of radar coherent backscattered signals in precipitation in the direction of wave propagation.

The theory is developed for the cross-correlation function of the complex amplitudes in the direction of propagation calculated for nearest neighbor range bins. Data are analyzed …

On The Enhanced Temporal Coherency Of Radar Observations In Precipitation, A. R. Jameson, A. B. Kostinski

Department of Physics Publications

In this work, the authors present observations of enhanced temporal coherency beyond that expected using the observations of the standard deviation of the Doppler velocities and the assumption of a family of exponentially decaying autocorrelation functions. The purpose of this paper is to interpret these observations by developing the complex amplitude autocorrelation function when both incoherent and coherent backscatter are present. Using this expression, it is then shown that when coherent scatter is present, the temporal coherency increases as observed. Data are analyzed in snow and in rain. The results agree with the theoretical expectations, and the authors interpret this …

Partially Coherent Backscatter In Radar Observations Of Precipitation, A. R. Jameson, A. B. Kostinski

Department of Physics Publications

Classical radar theory only considers incoherent backscatter from precipitation. Can precipitation generate coherent scatter as well? Until now, the accepted answer has been no, because hydrometeors are distributed sparsely in space (relative to radar wavelength) so that the continuum assumption used to explain coherent scatter in clear air and clouds does not hold.

In this work, a theory for a different mechanism is presented. The apparent existence of the proposed mechanism is then illustrated in both rain and snow. A new power spectrum Z( f ), the Fourier transform of the time series of the radar backscattered reflectivities, reveals …

Effects Of Deformation Ratio On The Mechanical Properties And Microstructures Changes In An Al-Mg-Si Alloy, Hichem Farh, Rebai Guemini, Serradj Fares, Karim Djemmal

Turkish Journal of Physics

An investigation has been done to study the effect of deformation ratio and two-step ageing treatment on the microstructure and the mechanical properties in an Al-Mg-Si aluminum alloy. Transmission electron microscopy is used in order to follow the distribution and the morphology of the hardening precipitates. The hardness of the alloy increases with the increasing deformation ratio. The maximum of hardness increases and is shifted to low time with an increase of the deformation ratio. The density of precipitates is more increased and the precipitates become more inhomogeneously distributed when the deformation combines with two-step ageing treatments.