Backscatter A [8101]--Offshore San Gregorio, California

This part of SIM 3306 presents data for the acoustic-backscatter map (see sheet 3, SIM 3306) of the Offshore of San Gregorio map area, California. Backscatter data are provided as two separate grids depending on mapping system (Reson 7125 and Reson 8101). The raster data file is included in "BackscatterA_8101_OffshoreSanGregorio.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSanGregorio/data_catalog_OffshoreSanGregorio.html.
The acoustic-backscatter map of the Offshore of San Gregorio, California was generated from backscatter data collected by Fugro Pelagos and by California State University, Monterey Bay (CSUMB). Mapping was completed in 2006 and 2007, using a combination of 400-kHz Reson 7125 and 244-kHz Reson 8101 multibeam echosounders. Within the final 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).

本数据集SIM 3306的此部分提供了加利福尼亚州圣格雷戈里奥近海制图区域的声学反向散射（acoustic-backscatter）地图相关数据（详见SIM 3306第3页）。根据测绘系统的不同，反向散射数据分为两个独立网格，分别对应Reson 7125与Reson 8101型号设备。栅格数据文件包含于"BackscatterA_8101_OffshoreSanGregorio.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreSanGregorio/data_catalog_OffshoreSanGregorio.html获取。

加利福尼亚州圣格雷戈里奥近海的声学反向散射地图，由Fugro Pelagos与蒙特雷湾加利福尼亚州立大学（CSUMB）采集的反向散射数据生成。测绘工作于2006年和2007年完成，采用了400kHz的Reson 7125与244kHz的Reson 8101多波束测深仪（multibeam echosounders）组合方案。在最终成像成果中，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以及浅表层地下特征之间的复杂相互作用，可用于大致指示海底的质地与组成。反向散射强度受多项因素影响：声源级、海底成像所用频率、掠射角、海底的组成与特征（包括粒度、含水率、体积密度以及海底粗糙度），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），而松软的底质类型（如细粒沉积物）则会返回较弱的信号（低反向散射，色调偏暗）。