Direction of Arrival Estimation Based on Delayed-Sum Method in Reverberation Environment

Abstract

High resolution far ultraviolet (12W2000,4) spectra of 17 cool giant and supergiant stars have been obtained using the IUE satellite of ESA, NASA and UK. We have measured the line intensities, wavelengths and widths of approximately 200 EUV emission lines in these spectra, using a least squares gaussian fitting technique. Line identification has been obtained in about one third of the cases. The measured values are organized in a database in order to facilitate updating and investigation of interrelations with stellar atmospheric parameters.The observations include lines from C I. C 11, C IV, S I, 0 I, 0 IV, Si 11, Si IV, N V, A1 111. Fe I1 and Mg 11. These lines are mostly formed by radiative processes in the extremely rarefied plasma in the outer stellar atmospheres, and occasionally involve highly excited energy levels of the atoms and ions. The temperature of formation ranges from about 5 x lo' to IO5 K, corresponding to different depth levels in the atmosphere, and the lines serve as a valuable tool for probing the physical conditions in these regions. We may also get new information on atomic processes that take place under conditions that are never duplicated in the laboratory. The present data may therefore give important contributions both to astrophysics and to atomic physics.

Passive Acoustic Source Localization at a Low Sampling Rate Based on a Five-Element Cross Microphone Array

“…Finally, through Fourier inverse transform of the weighted cross-correlation spectrum function, the generalized cross-correlation function is defined as: where G x 1 x 2 ( f ) is the cross-correlation spectrum density function, Ψ x 1 x 2 ( f ) is a weighting function and f is the frequency variable. For many different weighing functions, a commonly-used weighting function in acoustic event localization is the phase transform (PHAT), which is usually considered useful in reverberant conditions [ 10 ] and has low computational complexity and a higher recognition rate [ 3 , 4 ]. It can be described with the following equation: …”

“…Considering the acoustic source as a point source and the microphone M 0 as a reference point, thus according to Distance = Time × Speed and the geometrical model of the five-element cross microphone array, the localization equations are written as: where r is the distance between the acoustic source and the coordinate origin, τ i ( i = 1, 2, 3, 4) is the time delay between microphone M 0 and M i ( i = 1, 2, 3, 4) and c is sound velocity (in this paper c = 340 m/s) and under the assumptions of a constant speed for an indoor experiment and a near-field source localization [ 4 , 14 , 15 ]. In addition, there is mathematical relationship between the Cartesian coordinates and the spherical coordinates obtained by Equation (15) : …”

“…In general, the generalized cross-correlation (GCC) method is applied to estimate the TDOA. In practice, the performance of time delay estimation based on the GCC method is dependent on the sampling rate [ 3 ], namely a high sampling rate [ 4 – 6 ] can contribute to a high localization accuracy. However, some localization systems (e.g., wearable localization systems, hearing aid and human-computer interactions) tend to be small and portable with the development of the integrated circuit, electronic and computer technology, etc .…”

Localization of Acoustic Reflective Boundary Using a Pair of Microphones and an Arbitrary Sound Source

“…Authors have been developing a method of estimating the DOA of the direct sound, d , separated from the effects of reflected sound in reflective environments by using a microphone array consisting of at least two elements. 28) In this method, DOA is estimated by measuring the time difference of arrival between microphones corresponding to the direct sound, d . Moreover, we can also estimate the DOA of the reflected sound, r , by measuring the time difference of arrival between microphones corresponding to the reflected sound, 2 À 1 .…”

Simultaneous Measurement of Air Temperature and Humidity Based on Sound Velocity and Attenuation Using Ultrasonic Probe

“…Ultrasonic propagation characteristics in various mediums can be applied in measurements of physical quantities of mediums, such as water flow velocity, 1) wind velocity, 2) soil moisture, and groundwater level. 3) Ultrasonic measurements in mediums can also be applied for solid form estimations, 4,5) and detections of defects in solid materials. 6,7) In this paper, we focus on air as the medium, and air temperature and humidity measurement techniques are described.…”