Acoustic-reflection profiling

The present configuration of the surface of the glacial drift in Long Island Sound is a deep central basin bounded by sills on the east and west. The submergence history of the Sound depends on the elevations of the lowest points on these sills relative to the sea level curve. On the Mattituck sill (to the east) this elevation is now -25 m. Sand is now being transported from east to west across the Mattituck sill and it is possible that the sill is now at a higher elevation than it was immediately after retreat of the ice. (More detailed acoustic reflection profile studies of the internal structure of the sill may answer this question.) The lowest point on the sill to the west (which has not yet been surveyed in as much detail) is higher than -20 m. (The locations of the saddle points on the eastern... 

Fig. 13. Structure of the bottom of Long Island Sound revealed by acoustic reflection profiles made with 7-kHz acoustic pulses. (Upper echo is produced by a 2(X)-kHz echo sounder.) (a) Section of end moraine capped by boulders and almost buried by marine mud. (b) Thick deposit of marine mud in central Long Island Sound on top of outwash sand with reflector above thought to be surface of lacustrine deposits, (c) Sand-to-mud transition zone in central Long Island Sound. In all records each division on the vertical scale is 600 mm.

Doppler Flow Meters. Doppler flow meters sense the shift in apparent frequency of an ultrasonic beam as it is reflected from air bubbles or other acoustically reflective particles that ate moving in a Hquid flow. It is essential for operation that at least some particles ate present, but the concentration can be low and the particles as small as ca 40 p.m. CaUbration tends to be influenced by particle concentration because higher concentrations result in mote reflections taking place neat the wall, in the low velocity portion of the flow profile. One method used to minimize this effect is to have separate transmitting and receiving transducers focused to receive reflections from an intercept zone neat the center of the pipe. 

BSR An abbreviation for the so-called bottom simulating reflection. A reflection recorded in seismic reflection profiles that results from an acoustic velocity contrast produced by the decrease in sound speed caused primarily by the presence of gas trapped beneath the gas hydrate stability zone. BSRs provide a remotely sensed indication of the presence of gas hydrate. 

Examples are Laser Differential Microanemometry (LMA) and Total Reflection Microscopy (TMA) (8). Both LMA and TMA measure the velocity profile of the fluid in tube flow. However, such optical techniques are generally not suitable for opaque and/or heterogeneous substances such as foods. Acoustic velocimetry seems to be more promising for determining the velocity profiles of opaque substances. Such an acoustic technique has been applied by Brunn et al (19) as an on-line viscometer for flow of mayonnaises in pipes. 

An application of ultrasound that is becoming increasingly popular in the food industry is the determination of creaming and sedimentation profiles in emulsions and suspensions (Basaran et al., 1998). Acoustic techniques can also assess nondestructively the texture of aerated food products such as crackers and wafers. Air cells, which are critical to consumer appreciation of baked product quality, are readily probed due to their inherent compressibility (Elmehdi et al., 2003). Kulmyrzaev et al. (2000) developed an ultrasonic reflectance spectrometer to relate ultrasonic reflectance spectra to bubble characteristics of aerated foods. Experiments were carried out using foams with different bubble concentration and the results showed that ultrasonic reflectance spectrometry is sensitive to changes in bubble size and concentration of aerated foods. 

The numerical results obtained from simultaneous integration of (1) and (7) are shown in figs 1—3 for a planar cavity cluster at Pm = 20-103 Pa with f = a /27r = 20 kHz when = 0.3 mm. It is apparent from fig. 1 that initially the tensile stress in the cluster drops exponentially with the distance from the cluster boundary [1], but after 4 fjs the pressure profile steepens near the boundary due to the significant growth of the cavities here. The tensile stress decays beyond the first few cavity "layers" where growth of the cavities primarily occurs. The profile of increase of cavity radius vs. position is found to be essentially exponential, fig. 2. The pressure assumed from (15) is set up if an incident acoustic wave with a pressure Api vs. time t as shown in fig. 3 reaches the cluster boundary. It is noticed that very quickly the reflection coefficient approaches —1, showing that the boundary becomes an essentially compliant interface. 

At first, we applied the Cole formulations. Figure 5 shows the pressure profile used. The reflection of Initial shock wave Is considered as total, and In the acoustic approximation this reflection Is assumed to happen as that of light on a mirror. It Is considered that the pressure of expansion wave Is that of a wave generated by an Identical source, symmetrical with regard to the free surface. In the same boundary free liquid. After reflection the resulting pressure at a point under surface will be equal to the algebraic sum of pressures (Incident and reflected waves Including values of hydrostatic and... 

The seismic reflection method, also called sub bottom profiling, involves the recording of the travel time interval of seismic (acoustic) waves, which are emitted from the surface and reflected by the seabed and underlying soil layers. A seismic source generates a seismic (acoustic) signal with a relative high frequency. 

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