Backscatter C [Swath]--Offshore of Bodega Head, California

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Bodega Head map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data file is included in "BackscatterC_Swath_OffshoreBodegaHead.zip", which is accessible from http://pubs.usgs.gov/ds/781/OffshoreBodegaHead/data_catalog_OffshoreBodegaHead.html. The acoustic-backscatter map of the Offshore of Bodega Head map area, California, was generated from backscatter data collected by California State University, Monterey Bay (CSUMB), and by Fugro Pelagos. Mapping was completed between 2007 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 468-kHz SEA SWATHPlus interferometric system. These mapping missions combined to collect backscatter data (sheet 3) from about the 10-m isobath to beyond the 3-nautical-mile limit of California State Waters. Within the acoustic-backscatter imagery, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, providing a general indication of seafloor texture and composition. Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker tones). These data are not intended for navigational purposes.本数据集DS 781的此部分内容，提供了加利福尼亚州博德加角近海测绘区域的声学反向散射（acoustic-backscatter）地图数据。反向散射数据将根据测绘系统或处理方法分为独立的网格数据集。相关栅格数据文件收录于"BackscatterC_Swath_OffshoreBodegaHead.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreBodegaHead/data_catalog_OffshoreBodegaHead.html获取。 加利福尼亚州博德加角近海测绘区域的声学反向散射地图，由加州州立大学蒙特雷湾分校（California State University, Monterey Bay, CSUMB）与Fugro Pelagos采集的反向散射数据生成。本次测绘工作于2007年至2010年间完成，使用了200kHz与400kHz的Reson 7125多波束测深仪（multibeam echosounders）、244kHz的Reson 8101多波束测深仪，以及468kHz的SEA SWATHPlus干涉测量系统（interferometric system）。此次测绘任务共采集了约10米等深线（isobath）至加州领海3海里（nautical-mile）以外区域的反向散射数据（图幅3）。在声学反向散射影像中，色调越亮代表反向散射强度越高，色调越暗则代表反向散射强度越低。该强度反映了声波脉冲与海底及浅表层地下特征之间的复杂相互作用，可用于大致指示海底的纹理与组成成分。反向散射强度受多种因素影响：包括声源级、海底成像所用频率、掠射角、海底的组成与特征（如粒径、含水量、堆积密度（bulk density）以及海底粗糙度），以及部分生物覆盖物。质地坚硬粗糙的底质类型（如岩石露头或粗粒沉积物）通常会返回更强的信号（高反向散射，色调偏亮），而质地较软的底质类型（如细粒沉积物）则会返回较弱的信号（低反向散射，色调偏暗）。本数据集并非用于导航用途。