BackscatterA [SWATH]--Offshore Aptos, California

This part of DS 781 presents data for the acoustic-backscatter map of Offshore of Aptos map area, California. Backscatter data are provided as two separate grids depending on mapping system and processing method. The raster data files are included in "BackscatterA_SWATH_OffshoreAptos.zip," which is accessible from http://dx.doi.org/10.5066/F7K35RQB. The acoustic-backscatter map of Offshore of Aptos, California was generated from backscatter data collected by the U.S. Geological Survey (USGS) and by Monterey Bay Aquarium Research Institute (MBARI). Mapping was completed between 1998 and 2009, using a combination of a 234-kHz SWATHplus bathymetric sidescan-sonar system and a 30-kHz Simrad EM-300 multibeam echosounder. 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).DS 781的本章节提供了加利福尼亚州阿普托斯近海测绘区域的声学背散射（acoustic-backscatter）地图数据。根据所采用的测绘系统与处理方法，背散射数据分为两个独立网格数据集。相关栅格数据文件收录于"BackscatterA_SWATH_OffshoreAptos.zip"压缩包中，可通过链接http://dx.doi.org/10.5066/F7K35RQB获取。 加利福尼亚州阿普托斯近海的声学背散射地图，其数据由美国地质调查局（U.S. Geological Survey, USGS）与蒙特雷湾水族馆研究所（Monterey Bay Aquarium Research Institute, MBARI）采集的背散射数据生成。该测绘工作于1998年至2009年间完成，采用了234kHz的SWATHplus水深侧扫声呐系统与30kHz的Simrad EM-300多波束测深仪组合方案。在最终成像成果中，色调越亮代表背散射强度越高，色调越暗则代表背散射强度越低。该强度值反映了声学脉冲与海底及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。背散射强度受多类因素影响：声源级、海底成像所用频率、掠射角（grazing angle）、海底组成与特性（包括粒度、含水量、体积密度及海底粗糙度），以及部分生物覆盖物。质地坚硬且表面粗糙的底质类型（如岩层出露或粗颗粒沉积物）通常会返回更强的信号（高背散射，对应较亮色调），而松软底质（如细颗粒沉积物）则会返回较弱的信号（低背散射，对应较暗色调）。