The use of high-frequency acoustic techniques for detection and study of submerged objects and geological features in rivers can be limited by both attenuation and reverberation. These parameters were measured in a pilot study of the lower reaches of the Brazos River near Houston, Tex. The attenuation was due to the suspended particulate matter carried by this muddy river. At a frequency of 200 kHz and for a particulate concentration of 0.025% by weight, the attenuation was found to be 1.5 dB/100 yd. Reverberation from the bottom sediment was measured at a frequency of 85 kHz as a function of transducer grazing angle. The reverberation data are interpreted as a scattering strength per unit area of bottom insonification and fall in the range of scattering strengths reported by others for fine mud. [This work was supported by the Office of Naval Research.]
The sidelobe level sensitivity of multistage modulation scanning sonar systems to internal electronic phase errors is examined by means of a "scanning function" approach and also by a hardware oriented analysis of a particular sonar system. It is shown that the later internal stages of such modulation scanning systems are the most sensitive to phase error. A general approach to calculating scanning sidelobe levels with phase error present is discussed.
The vertical side-lobe structure of cylindrical arrays driven in phase is examined. Experimental results demonstrate that the vertical side-lobe levels are significant when the angular aperture of the array is large.The physical cause of this phenomenon is identified, and a method of eliminating excessi•,e side-lobe levels is explained. Experimental results showing that this method is successful are presented. PACS numbers: 43.30 Yj, 43.30 Vh.
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