Backscatter B [USGS]--Offshore of Coal Oil Point, California

This part of SIM 3302 presents data for part of the acoustic-backscatter map (see sheet 3, SIM 3302) of the Offshore of Coal Oil Point map area, California. The raster data file is included in "BackscatterB_USGS_OffshoreCoalOilPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreCoalOilPoint/data_catalog_OffshoreCoalOilPoint.html.
The acoustic-backscatter map of the Offshore of Coal Oil Point map area, California, was generated from backscatter data collected by California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB), by the U.S. Geological Survey (USGS), and by Fugro Pelagos. These metadata describe the acoustic-backscatter data collected by the USGS. See "BackscatterA_CSUMB_OffshoreCoalOilPoint_metadata.txt" metadata for a description of the acoustic-backscatter data collected by CSUMB, and see "BackscatterC_Fugro_OffshoreCoalOilPoint_metadata.txt" metadata for a description of the acoustic-backscatter data collected by Fugro Pelagos. Most of the nearshore and shelf areas in the Offshore of Coal Oil Point map area were mapped by the USGS in the summers of 2006, 2007, and 2008, using a combination of 117-kHz and 234.5-kHz SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonars. 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 sediment type. 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 3302的此部分包含美国加利福尼亚州科伊油点近海（Offshore of Coal Oil Point）制图区域的部分声反向散射（acoustic-backscatter）地图数据（详见SIM 3302第3页）。栅格数据文件收录于"BackscatterB_USGS_OffshoreCoalOilPoint.zip"压缩包中，该文件可通过http://pubs.usgs.gov/ds/781/OffshoreCoalOilPoint/data_catalog_OffshoreCoalOilPoint.html获取。

加利福尼亚州科伊油点近海制图区域的声反向散射地图，由加州州立大学蒙特雷湾分校海底测绘实验室（CSUMB）、美国地质调查局（U.S. Geological Survey, USGS）以及Fugro Pelagos三家机构采集的反向散射数据生成。本元数据仅对美国地质调查局采集的声反向散射数据进行说明。如需了解加州州立大学蒙特雷湾分校海底测绘实验室采集的声反向散射数据详情，请参阅"BackscatterA_CSUMB_OffshoreCoalOilPoint_metadata.txt"元数据文件；如需了解Fugro Pelagos采集的声反向散射数据详情，请参阅"BackscatterC_Fugro_OffshoreCoalOilPoint_metadata.txt"元数据文件。

科伊油点近海制图区域的多数近岸与陆架区域，由美国地质调查局于2006、2007及2008年夏季，结合使用117kHz与234.5kHz频段的SEA (AP) Ltd. SWATHplus-M相位差分侧扫声呐完成测绘。

在声反向散射影像中，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以及浅地下地层特征之间的复杂相互作用，可用于大致推断海底质地与沉积物类型。

反向散射强度受以下因素影响：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。

质地坚硬且粗糙的海底类型（如岩层出露区域或粗粒沉积物）通常会返回更强的散射强度（高反向散射，对应亮色调）；而质地柔软的海底类型（如细粒沉积物）则会返回较弱的散射强度（低反向散射，对应暗色调）。