测量动光栅瞬时速度的有效方法

激光束通过双光栅衍射,衍射光束重叠形成光拍,光拍信号通过硅光电池进行光电转换,得到的信号电流的频率等于多普勒频移.信号电流经I/V转换、反函数电路和微分及计算电路运算后,可以确定多普勒频移,从而确定动光栅的运动速度.测量了音叉在换能器的作用下做微振动时动光栅的瞬时速度.     

Acoustic sounding of wind velocity profiles in a stratified moving atmosphere.

The paper deals with analytical and numerical studies of the effects of atmospheric stratification on acoustic remote sensing of wind velocity profiles by sodars. Both bistatic and monostatic schemes are considered. Formulas for the Doppler shift of an acoustic echo signal scattered by atmospheric turbulence advected with the mean wind in a stratified moving atmosphere are derived. Numerical studies of these formulas show that errors in retrieving wind velocity can be of the order of 1 m/s if atmospheric stratification is ignored. Formulas for the height at which wind velocity is retrieved are also derived. Approaches are proposed which allow one to take into account the effects of atmospheric stratification when restoring the wind velocity profile from measured values of the Doppler shift and the time interval of acoustic impulse propagation from a sodar to the scattering volume and back to the ground.     

A unified model for reverberation and submerged object scattering in a stratified ocean waveguide

A unified model for reverberation and submerged target scattering in a stratified medium is developed from wave theory. The advantage of the unified approach is that it enables quantitative predictions to be made of the target-echo-to-reverberation ratio in an ocean waveguide. Analytic expressions are derived for both deterministic and stochastic scattering from the seafloor and subseafloor. Asymptotic techniques are used to derive expressions for the scattering of broadband waveforms from distant objects or surfaces. Expressions are then obtained for the scattered field after beamforming with a horizontal line array. The model is applied to problems of active detection in shallow water. Sample calculations for narrow-band signals indicate that the detection of submerged target echoes above diffuse seafloor reverberation is highly dependent upon water column and sediment stratification as well as array aperture, source, receiver, and target locations, in addition to the scattering properties of the target and seafloor. The model is also applied to determine the conditions necessary for echo returns from discrete geomorphologic features of the seafloor and subseafloor to stand prominently above diffuse seafloor reverberation. This has great relevance to the geologic clutter problem encountered by active sonar systems operating in shallow water, as well as to the remote sensing of underwater geomorphology.     

Transition through the critical velocity for a moving load in an elastic waveguide

Phenomena that accompany the transonic transition experienced by a load moving along a string on a deformed base are studied. A solution in the form convenient for a qualitative analysis of the wave processes is proposed. The cases of the acceleration and deceleration of the load are considered.     

Differential velocity thresholds for an auditory target moving in the vertical plane

Acoustical Physics - Differential sensitivity to the velocity of an auditory target moving in the vertical plane and the effect of the direction of motion and of the signal spectrum on the...     

Focusing of acoustic fields in a randomly inhomogeneous waveguide by using the time reversal method

We perform theoretical analysis of the method of field focusing in a randomly inhomogeneous waveguide using reradiation of the received signal with time reversal. The simplest case where point sources and receivers are used for emission and reception is considered. As an example, the waveguide is chosen which simulates an underwater sound channel with refractive-index fluctuations caused by random internal waves. In underwater acoustics, the considered method of field focusing is usually applied at relatively short distances that are shorter than or about 10 km. This work deals with much longer paths, along which sound waves propagate under conditions of well-developed ray and wave chaos. Main attention is given to studying the width of the focal spot and the field amplitude at its center. It is shown that the amplitude distribution in the vertical section of the focal spot and the peak amplitude value at its center can be estimated analytically using the stochastic ray theory.     

Traces of a tsunamigenic earthquake in a rotating stratified ocean

In the framework of the linear long-wave theory, we derive a system of equations that describe the potential and vortex residual hydrodynamic fields that arise in a rotating stratified (two-layer) ocean during tsunami generation by coseismic deformations of the ocean bottom. For the model case of a cylindrically symmetric ocean bottom deformation, we find an approximate analytical solution of the problem. Based on this solution, we analyze the specific features of residual fields due to the presence of stratification for conditions that are typical of real tsunami sources.     

动摄像机和动目标跟踪模式下的目标检测新方法

动摄像机和动目标跟踪是图像分析中的一个难点。根据应用光学知识和坐标变换理论,提出了映射变换差分方法(mappingtransformationdifferentialmethod,MTDM)。该方法首先利用映射变换将动摄像机和动目标模式下的目标检测问题转化为技术比较成熟的静摄像机和动目标模式下的目标检测,然后利用图像差分方法检测出被跟踪目标。实验结果表明:MTDM方法在复杂天空背景下能有效地抑制背景噪声,能准确地检测出被跟踪目标。     

Electromagnetic field generated by a modulated moving point source in a planarly layered waveguide

In the present work, we consider a modulated point source in an arbitrary motion in an isotropic planarly layered waveguide. The radiation field generated by this source is represented in the form of double oscillatory integrals in terms of the time and the frequency, depending on the large parameter λ. By means of the stationary phase method, we analyze, in the waveguide, the Doppler effect, the retarded time, and the Vavilov–Cherenkov radiation. Numerically, the problem of the moving source is approached by the method of spectral parameter power series.