Backscatter A [CSUMB]--Offshore of Ventura, California

This part of SIM 3254 presents data for part of the acoustic-backscatter map (see sheet 3, SIM 3254) of the Offshore of Ventura map area, California. The raster data file is included in "BackscatterA_CSUMB_OffshoreVentura.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html.
The acoustic-backscatter map of the Offshore of Ventura map area, California, was generated from backscatter data collected by California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB) and by the U.S. Geological Survey (USGS). These metadata describe the acoustic-backscatter data collected by CSUMB and reprocessed by the USGS (see "BackscatterB_USGS_OffshoreVentura_metadata.txt" metadata for a description of the acoustic-backscatter data collected by the USGS). The majority of the acoustic-backscatter data within the Offshore of Ventura map area, California, was collected by CSUMB in the summers of 2006 and 2007, using a 244-kHz Reson 8101 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 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SIM 3254数据集的此部分提供了加利福尼亚州文图拉近海制图区部分声散射地图（详见SIM 3254第3幅图）的数据。栅格数据文件包含于"BackscatterA_CSUMB_OffshoreVentura.zip"压缩包中，可通过http://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html获取。

加利福尼亚州文图拉近海制图区的声散射地图，由加利福尼亚州立大学蒙特利湾分校海底测绘实验室（California State University, Monterey Bay, Seafloor Mapping Lab，简称CSUMB）与美国地质调查局（U.S. Geological Survey，简称USGS）采集的背散射数据生成。本元数据描述了由CSUMB采集并经USGS重新处理的声散射数据；关于USGS采集的声散射数据的说明，请参阅"BackscatterB_USGS_OffshoreVentura_metadata.txt"元数据文件。

加利福尼亚州文图拉近海制图区内的大部分声散射数据，由CSUMB于2006年和2007年夏季使用244千赫兹Reson 8101型多波束测深仪采集。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。背散射强度反映了声脉冲与海底以及浅地表内部特征之间的复杂相互作用，可大致指示海底质地与沉积物类型。

背散射强度受多个因素影响：声学声源级、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）以及部分生物覆盖层。质地更坚硬、表面更粗糙的海底类型（如岩石露头或粗粒沉积物）通常会返回更强的信号强度（高背散射，对应亮色调），而质地较软的海底类型（如细粒沉积物）则会返回较弱的信号强度（低背散射，对应暗色调）。