BackscatterC [7125]--Offshore of Salt Point Map Area, California

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Salt Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files are included in "Backscatter7125_SaltPoint.zip", which are accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The acoustic-backscatter map of the Offshore of Salt Point 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 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.DS 781的本部分提供了加利福尼亚州盐角近海（Offshore of Salt Point）制图区域的声学反向散射（acoustic-backscatter）地图数据。反向散射数据依据制图系统或处理方法的不同，以独立网格文件形式提供。栅格数据文件存储于"Backscatter7125_SaltPoint.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html获取。 加利福尼亚州盐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雷湾分校（California State University, Monterey Bay, 简称CSUMB）与Fugro Pelagos公司采集的反向散射数据生成。制图工作于2007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。本次制图任务采集了约10米等深线至加州领海3海里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。该强度值反映了声脉冲与海底及浅地下层特性之间的复杂相互作用，可用于大致表征海底纹理与物质组成。反向散射强度受以下因素影响：声源级、海底成像所用频率、掠射角、海底物质组成与特性（包括粒径、含水率、体积密度及海底粗糙度），以及部分生物覆盖物。坚硬且粗糙的海底类型（如岩层出露或粗粒沉积物）通常会返回更强的信号（高反向散射，对应亮色调），而松软的海底类型（如细粒沉积物）则返回较弱的信号（低反向散射，对应暗色调）。本数据集不应用于导航目的。