Acoustic multibeam system for 3-dimensional bedform evolution studies

所要求的设备是一种高频声学多波束系统，用于以接近视频系统的帧率获取海底的高分辨率剖面。通过电子控制海底的声波束点，可以获得海床的高程剖面。基于早期设计的260千赫（6毫米波长）的声波频率，这种新开发的加拿大制造的传感器工作在2.25兆赫（0.7毫米波长），较短的波长提供了更高的空间分辨率。为了获得三维地图，声学传感器必须在与波束导向平面正交的方向上机械驱动，因此还需要资金购买用于此目的的旋转单元。这种组合的多波束/旋转系统将能够在几十秒内生成5米× 5米范围内的小尺度海底地形图，其水平分辨率为几厘米或更高，垂直分辨率优于1厘米。考虑到风致海潮的典型周期为10-s，这一获取时间与几个地面重力波的通过时间相当。因此，该系统将能够首次在波群的时间尺度上调查海底移动地形的演变。该系统将于2007年秋季进行为期2个月的部署，作为对粗粒和细粒沙的内大陆架上波浪形波纹的时间演变的调查的一部分。

The equipment requested is a high-frequency acoustic multibeam system for obtaining high-resolution profiles of the seafloor at frame rates approaching that of video systems. The bed elevation profile is obtained by steering the acoustic beam spot electronically over the seafloor. Based on an earlier design operating at an acoustic frequency of 260 kHz (6-mm wavelength), this newly-developed Canadian-built sensor operates at 2.25 MHz (0.7-mm wavelength), the shorter wavelength providing much higher spatial resolution. To obtain a 3-dimensional map, the acoustic sensor must be mechanically driven in a direction orthogonal to the beam-steering plane, and thus funds are also requested to purchase a rotator unit for this purpose.   The combined multibeam/rotator system will be capable of generating 3-d maps of the small-scale seafloor topography over a 5-m by 5-m area with a horizontal resolution of a few cm or better, and better than 1-cm vertical resolution, in tens of seconds. Given the 10-s typical periods of wind-generated sea-and-swell waves, this acquisition time is commensurate with the passage of several surface gravity waves. Thus, the system will enable first-time investigations of the evolution of mobile seafloor topography on the time scales of wave-groups. The system will be deployed in the fall of 2007 for 2 months as part of an investigation of the temporal evolution of wave-formed ripples on inner shelf in coarse- and fine-grained sands.