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).

本数据集为SIM 3254的一部分，提供了加利福尼亚州文图拉近海制图区域的部分声反向散射（acoustic-backscatter）地图数据（详见第3页，SIM 3254）。栅格数据文件收录于"BackscatterA_CSUMB_OffshoreVentura.zip"，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）与美国地质调查局（USGS）采集的反向散射数据生成。本元数据（metadata）用于描述由CSUMB采集、后经USGS重新处理的声反向散射数据；关于USGS直接采集的声反向散射数据的详细说明，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域的绝大多数声反向散射数据由CSUMB于2006年和2007年夏季采集，所用设备为244kHz Reson 8101多波束测深仪（multibeam echosounder）。
在最终生成的影像中，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。该强度值反映了声脉冲与海底及其浅表层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。反向散射强度受多重因素影响：声源级、海底成像所用声波频率、掠射角、海底的组成与特征（包括粒度、含水量、体积密度及海底粗糙度），以及海底的部分生物覆盖物。坚硬且粗糙的海底类型（如岩石露头或粗颗粒沉积物）通常会返回更强的信号（高反向散射，对应亮色调），而松软的海底类型（如细颗粒沉积物）则会返回较弱的信号（低反向散射，对应暗色调）。