BackscatterA [8210]--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 "Backscatter8101_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.

本DS 781数据集的此部分提供了加利福尼亚州盐点近海测绘区域的声学反向散射（acoustic-backscatter）地图数据。反向散射数据依据所采用的测绘系统或处理方法，以独立栅格的形式提供。栅格数据文件均打包于"Backscatter8101_SaltPoint.zip"中，可通过http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html获取。

加利福尼亚州盐点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（CSUMB）及辉固佩拉戈斯（Fugro Pelagos）采集的反向散射数据生成。测绘工作于2007至2010年间完成，使用了200kHz与400kHz的Reson 7125型、244kHz的Reson 8101型多波束测深仪，以及468kHz的SEA SWATHPlus干涉测量系统。本次测绘任务共收集了从约10米等深线至加州州管海域3海里界限以外区域的反向散射数据。

在该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之间，以及浅地表内部特征间的复杂相互作用，可大致体现海底的纹理与组成成分。反向散射强度取决于声源级、海底成像所用频率、掠射角、海底的组成与特征（包括粒径、含水率、体积密度及海底粗糙度），以及部分生物覆盖层。质地坚硬且粗糙的海底类型（如岩石露头或粗粒沉积物）通常会返回更强的强度（高反向散射，亮色调），而质地柔软的海底类型（如细粒沉积物）则会返回较弱的强度（低反向散射，暗色调）。本数据集并非用于导航用途。