Patel Ruben, Pedersen Geir, Ona Egil
Institute of Marine Research, Nordnes, Bergen, Norway.
J Acoust Soc Am. 2009 Feb;125(2):698-705. doi: 10.1121/1.3050325.
Acoustic measurement of near-bottom fish with a directional transducer is generally problematical because the powerful bottom echo interferes with weaker echoes from fish within the main lobe but at greater ranges than that of the bottom. The volume that is obscured is called the dead zone. This has already been estimated for the special case of a flat horizontal bottom when observed by an echo sounder with a stable vertical transducer beam [Ona, E., and Mitson, R. B. (1996). ICES J. Mar. Sci. 53, 677-690]. The more general case of observation by a split-beam echo sounder with a transducer mounted on a noninertial platform is addressed here. This exploits the capability of a split-beam echo sounder to measure the bottom slope relative to the beam axis and thence to allow the dead-zone volume over a flat but sloping bottom to be estimated analytically. The method is established for the Simrad EK60 scientific echo sounder, with split-beam transducers operating at 18, 38, 70, 120, and 200 kHz. It is validated by comparing their estimates of seafloor slope near the Lofoten Islands, N67-70, with simultaneous measurements made by two hydrographic multibeam sonars, the Simrad EM100295 kHz and EM30030 kHz systems working in tandem.
使用定向换能器对近海底鱼类进行声学测量通常存在问题，因为强大的海底回波会干扰来自主瓣内鱼类的较弱回波，这些鱼类位于比海底更远的距离处。被遮挡的区域称为盲区。对于使用稳定垂直换能器波束的回声测深仪观测到的平坦水平海底的特殊情况，已经对此进行了估计[奥纳，E.，和米特森，R. B.（1996年）。《国际海洋考察理事会海洋科学杂志》53卷，677 - 690页]。本文讨论了使用安装在非惯性平台上的换能器的分束回声测深仪进行观测的更一般情况。这利用了分束回声测深仪测量相对于波束轴的海底坡度的能力，从而能够通过分析估计平坦但倾斜海底上的盲区体积。该方法是针对Simrad EK60科学回声测深仪建立的，其分束换能器工作频率为18、38、70、120和200千赫。通过将它们在罗弗敦群岛（北纬67 - 70度）附近对海底坡度的估计与两台水文多波束声纳（Simrad EM1002 95千赫和EM300 30千赫系统协同工作）的同步测量结果进行比较，对该方法进行了验证。
