BackscatterA [8101]--Offshore Pacifica, California

This part of DS 781 presents data for the acoustic-backscatter map of Offshore of Pacifica map area, California. Backscatter data are provided as two separate grids depending on mapping system. The raster data files are included in "BackscatterA_8101_OffshorePacifica.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshorePacifica/data_catalog_OffshorePacifica.html.

The acoustic-backscatter map of the Offshore of Pacifica, California was generated from backscatter data collected by Fugro Pelagos and by California State University, Monterey Bay (CSUMB). Mapping was completed between 2005 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DS 781的此部分提供了加利福尼亚州帕西菲卡近海海域的声学反向散射（acoustic-backscatter）地图数据。根据测绘系统的不同，反向散射数据分为两个独立网格。栅格数据文件封装于"BackscatterA_8101_OffshorePacifica.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshorePacifica/data_catalog_OffshorePacifica.html获取。

加利福尼亚州帕西菲卡近海的声学反向散射地图，由Fugro Pelagos公司与加州州立大学蒙特利湾分校（California State University, Monterey Bay, CSUMB）采集的反向散射数据生成。测绘工作于2005年至2007年间完成，采用了400kHz Reson 7125与244kHz 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。该强度值反映了声脉冲与海底及其浅地下结构间的复杂相互作用，可用于大致表征海底的质地与组成。反向散射强度受多项因素影响：声源级、海底成像所用声波频率、掠射角、海底的组成与特征（包括沉积物粒径、含水率、堆积密度及海底粗糙度），以及部分生物覆盖物。通常，硬质粗糙底质（如岩层出露或粗颗粒沉积物）会返回更强的信号（高反向散射，色调偏亮），而软质底质（如细颗粒沉积物）则返回较弱的信号（低反向散射，色调偏暗）。