Bistatic Reverberation in Shallow Water：Modelling and Data Comparison

Bistatic and monostatic reverberation data were recorded in the 2001 Asian Sea International Acoustic Experiment (ASLIAEX).A model based on the normal mode theory has been developed to calculate bistatic bottom reverberation in shallow water and to explain the recorded data.The comparisons between the monostatic and bistatic reverberation data are discussed,and the comparisons between model predictions and measured bistatic reverberation data are also presented.The numerical and experimental results show that the numerical predictions from the bistatic reverberation model fit the experimental data well,and the long-range bistatic reverberation with a time delay can be approximately expressed by the monostatic reverberation data.     

THE MEASUREMENTS OF TWO-DIMENSIONAL BOTTOM BACKSCATTERING COEFFICIENTS AT SHALLOW WATER

A frame with ten vertically spaced transducers was mounted on the sea floor to measure thebottom backscattering.The operating frequency was 10 kHz and the bottom backscattering coefficientswere measured as a function of both incident and scattering grazing angles(0.6°—40°).Meanwhile,the bottom reflection coefficients and reverberation intensities were also measured in the same areaunder the condition of thermocline.By feeding the measured bottom reflection and scattering coef-ficients as well as the sound-speed profile into the reverberation model,we have estimated the rever-beration intensities,which are in good agreement with the experimental data.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Dre11-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Dre11-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions shoul““““d not include Dre11-Yan experimental data.     

Energy Loss of Fast Quarks in Nuclear Drell-Yan Dimuon Production

The energy loss effect in nuclear matter, which is another nuclear effect apart from the nuclear effects on the patton distribution as in the deep inelastic scattering process, can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of the quark energy loss parametrization given in literature and the nuclear patton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Drell-Yan production cross sections are analysed for 800-GeV protons incident on a variety of nuclear targets from FNAL E866. The average energy loss of quarks are given by fitting the Fe/Be and W/Be Drell-Yan cross section ratios versus the incident patton momentum fraction.     

Adaptive nonlinear prediction of ocean reverberation

An adaptive nonlinear prediction algorithm is proposed to predict ocean reverberation based on the phase space reconstruction of nonlinear dynamic system. The prediction algorithm is tested by experimental reverberation data measured in two areas, and the one-step forward prediction results are in good agreement with the experimental data. If the errors between the predicted and experimental data are chosen as the variable to detect the target in the reverberation series, the reverberation is suppressed and the signal-to-reverberation ratio is improved.     

Extraction of mode attenuation coefficient from low frequency reverberation signal

A method of extracting normal mode attenuation coefficient from low frequency reverberation signal has been proposed.Pseudo-inverse normal mode filtering method is implemented to get single mode reverberation field firstly.Based on the assumption of separability of modal back-scattering matrix,effective back-scattering matrix element can be calculated using single mode average reverberation intensity.Finally,mode attenuation coefficient is extracted by comparing effective back-scattering matrix elements at different ranges.The extracted mode attenuation coefficients are used to predict sound transmission loss at the same experiment area. Results show that the predicted transmission loss agrees well with the measured data.This method avoids the difficult of treating the coupling between bottom scattering attenuation and normal mode propagation attenuation.Research on extraction of mode attenuation coefficient from low frequency reverberation signal is useful for both geoacoustic inversion and rapid underwater environment assessment.     

LONG-RANGE REVERBERATION AND BOTTOM SCATTERING STRENGTH IN SHALLOW WATER

According to the method of angular power spectrum for averaged sound field in shallow water,the transformation relation between arbitrary angle dependence of hottom scattering and the rangedependence of long-range reverberation in shallow water homogeneous layer is established.Ascompared with the conventional model of boundary reverberation at short range in deep sea,a multipath correction factor is added.By using the transformation relation,the bottombackscattering strength for the frequency band of 0.8—4.0kHz and grazing angle range of 2—10°has been derived from shallow-water reverberation data at five locations in the Yellow Sea,theBobai Sea and the East China Sea.It is shown that the bottom scattering constant(μ)and theangle index(2n)for high speed sediment of the continental shelf depend not only on sea area andfrqucncy,but also on angle range.     

Modeling of reverberation in shallow-water based on the beam tracing theory

A reverberation intensity model and a reverberation series model in shallow-water based on the beam tracing theory were presented.The brief theoretical deduction to compute reverberation intensity was given,and the results were compatible with the measured data. The reverberation series simulation method was built and its characteristics were tested with the measured data and other results that had been verified.The studies show that the reverberation intensity model can be used to forecast shallow-water reverberation intensity,and the reverberation series simulation method can generate reverberation series which mostly properties, such as probability distribution,time-varying spectrum,and spatial correlation,agree well with the measure and the theory.     

Static light scattering properties of a ZnO nanosphere aqueous suspension at visible and near-infrared wavelengths

The scattering properties of ZnO nanospheres with four different particle diameters of 10, 50, 100, and 200 nm suspended in water are investigated theoretical and experimentally in the spectral range of the entire visible range and part of the near-infrared region. The scattering properties of ZnO nanospheres suspended in water are described by employing three main parameters: the angular distribution of the scattering intensity I, the scattering extinction coefficient αscat, and the scattering cross section σscat. The results indicate that(i) at a certain wavelength, the angular distribution of the scattering intensity appears as an obviously forwardpropagating feature, and the forward-scattering intensity is dominant gradually when the particle diameter increases from 10 to 200 nm, and(ii) the scattering extinction coefficient and cross section can be determined by using the measured transmittance changes of a pure water sample and a given ZnO sample; they all are shown to be dependent on the particle size and incident wavelength. The experimental results of four different scattering samples agree well with the theoretical predictions within the given wavelength range.     

Influence of quark energy loss on extracting nuclear sea quark distribution from nuclear Drell-Yan experimental data

By means of two typical kinds of quark energy loss parametrization and the nuclear parton distributions determined only with lepton-nuclear deep inelastic scattering experimental data, a leading order analysis is performed on the proton-induced Drell-Yan differential cross section ratios of tungsten versus deuterium as a function of the quark momentum fraction in the beam proton and target nuclei. It is found that the theoretical results with quark energy loss are in good agreement with the experimental data. The quark energy loss effect produces approximately 3% to 11% suppression on the Drell-Yan differential cross section ratios R_W/D in the range 0.05≤x₂≤0.3. The application of nuclear Drell-Yan data with heavy targets is remarkably subject to difficulty in the constraint of the nuclear sea quark distribution.