BackscatterA [8101]--Offshore of Point Reyes Map Map Area, California

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Point Reyes map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files are included in "BackscatterA_8101_PtReyes.zip", which are accessible from http://pubs.usgs.gov/ds/781/OffshorePointReyes/data_catalog_PointReyes.html The acoustic-backscatter map of the Offshore of Point Reyes 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 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). NOTE: the horizontal datum of the backscatter data (NAD83) differs from the horizontal datum of other layers in this DS (WGS84). These data are not intended for navigational purposes.本数据集为DS 781的组成部分，提供加利福尼亚州雷耶斯角近海制图区的声学反向散射（acoustic-backscatter）地图数据。反向散射数据根据制图系统或处理方法分为独立栅格网格。栅格数据文件包含于"BackscatterA_8101_PtReyes.zip"压缩包中，可通过以下链接获取：http://pubs.usgs.gov/ds/781/OffshorePointReyes/data_catalog_PointReyes.html 加利福尼亚州雷耶斯角近海制图区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）与富格罗佩拉戈斯（Fugro Pelagos）采集的反向散射数据生成。制图工作于2007年至2010年间完成，所用设备包括200kHz与400kHz型号Reson 7125多波束测深仪、244kHz型号Reson 8101多波束测深仪，以及468kHz型号SEA SWATHPlus干涉测量系统。本次制图任务共采集了从约10米等深线至超出加利福尼亚州海域3海里边界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表内部特征间的复杂相互作用，可用于大致指示海底纹理与组成成分。反向散射强度受多重因素影响：声源级、海底成像所用频率、掠射角、海底的组成与特征（包括粒径、含水量、体积密度及海底粗糙度），以及部分生物覆盖物。质地坚硬且粗糙的底质（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），而质地柔软的底质（如细粒沉积物）则会返回较弱的信号（低反向散射，色调偏暗）。 注意：本数据集的反向散射数据采用的水平基准面为NAD83，与本DS中其他图层的水平基准面WGS84不一致。本数据不得用于导航用途。