Backscatter B [7125]--Offshore of Tomales Point, California

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Tomales Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data file is included in "BackscatterB_7125_OffshoreTomalesPoint.zip", which is accessible from http://pubs.usgs.gov/ds/781/OffshoreTomalesPoint/data_catalog_OffshoreTomalesPoint.html.

The acoustic-backscatter map of the Offshore of Tomales Point map area, California, was generated from backscatter data collected by California State University, Monterey Bay (CSUMB), by Fugro Pelagos, and by the U.S. Geological Survey. Mapping was completed between 2004 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 234-kHz and 468-kHz SEA SWATHPlus phase-differencing sidescan sonars. These mapping missions combined to collect backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California's 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.

本数据集为DS 781的组成部分，提供加利福尼亚州托马利斯角近海制图区域的声学反向散射（acoustic-backscatter）地图数据。反向散射数据按照制图系统或处理方法分为独立栅格数据集。栅格数据文件存储于"BackscatterB_7125_OffshoreTomalesPoint.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreTomalesPoint/data_catalog_OffshoreTomalesPoint.html获取。

加利福尼亚州托马利斯角近海制图区域的声学反向散射地图，由加州州立大学蒙特利湾分校（California State University, Monterey Bay, CSUMB）、富格罗佩拉戈斯（Fugro Pelagos）与美国地质调查局（U.S. Geological Survey）采集的反向散射数据生成。制图工作于2004至2010年间完成，所用设备包括200kHz与400kHz的Reson 7125多波束测深仪、244kHz的Reson 8101多波束测深仪，以及234kHz与468kHz的SEA SWATHPlus相位差分侧扫声呐。本次制图任务共采集了覆盖约10米等深线至超出加利福尼亚州海域3海里界限范围的反向散射数据。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。该强度反映了声脉冲与海底及浅地下特征之间的复杂相互作用，可大致指示海底纹理与组成成分。反向散射强度受多项因素影响：声学源级、海底成像所用频率、掠射角、海底的组成与特性（包括粒度、含水量、体积密度及海底粗糙度），以及部分生物覆盖物。坚硬且粗糙的底质类型（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），而柔软的底质类型（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目的。