BackscatterC [7125]--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 "BackscatterB_Swath_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DS 781数据集的本部分提供了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。反向散射数据根据测绘系统或处理方法的不同，以独立网格的形式提供。栅格数据文件存储于"BackscatterB_Swath_PtReyes.zip"压缩包中，可通过 http://pubs.usgs.gov/ds/781/OffshorePointReyes/data_catalog_PointReyes.html 获取。

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雷湾分校（California State University, Monterey Bay，CSUMB）与Fugro Pelagos采集的反向散射数据生成。该测绘工作于2007年至2010年间完成，使用了200kHz与400kHz的Reson 7125多波束测深仪、244kHz的Reson 8101多波束测深仪，以及468kHz的SEA SWATHPlus干涉测量系统。本次联合测绘任务采集了约10米等深线至加利福尼亚州海域3海里界限以外区域的反向散射数据。

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。反向散射强度反映了声脉冲与海底之间的复杂相互作用，以及浅地表的地层特征，可用于大致推断海底的纹理与组成物质。反向散射强度受多个因素影响：声源级、海底成像所用声波频率、掠射角、海底组成与特征（包括粒度、含水率、体积密度及海底粗糙度），以及海底生物覆盖情况。质地坚硬且粗糙的海底类型（如裸露岩床或粗粒沉积物）通常会产生更强的反向散射强度（高反向散射，色调偏亮），而质地柔软的海底类型（如细粒沉积物）则会产生较弱的反向散射强度（低反向散射，色调偏暗）。

注意：本数据集反向散射数据的水平基准面为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。