Backscatter C [8101]--Offshore of San Francisco, California

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of San Francisco map area, California. Backscatter data are provided as separate grids depending on mapping system used and processing techniques. The raster data file is included in "BackscatterC_8101_2008_OffshoreSanFrancisco.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSanFrancisco/data_catalog_OffshoreSanFrancisco.html. The acoustic-backscatter map of the Offshore of San Francisco Map Area, California was generated from backscatter data collected by Fugro Pelagos and by California State University, Monterey Bay (CSUMB). Mapping was completed between 2004 and 2008, 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DS 781的此部分提供了加利福尼亚州旧金山近海制图区域的声学反向散射（acoustic-backscatter）地图数据。反向散射数据根据所采用的制图系统与处理技术，以独立栅格形式提供。栅格数据文件包含于"BackscatterC_8101_2008_OffshoreSanFrancisco.zip"中，可通过http://pubs.usgs.gov/ds/781/OffshoreSanFrancisco/data_catalog_OffshoreSanFrancisco.html获取。 加利福尼亚州旧金山近海制图区域的声学反向散射地图，由Fugro Pelagos与加州州立大学蒙特雷湾分校（California State University, Monterey Bay, CSUMB）采集的反向散射数据生成。制图工作于2004至2008年间完成，采用了400kHz Reson 7125与244kHz Reson 8101多波束测深仪的组合方案。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。该强度值反映了声脉冲与海底、浅地下层特征之间的复杂相互作用，可用于大致表征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。通常而言，硬质粗糙底质（如岩石露头或粗颗粒沉积物）会返回更强的信号强度（高反向散射，对应亮色调），而软质底质（如细颗粒沉积物）则返回较弱的信号强度（低反向散射，对应暗色调）。