Tracklines of Sidescan-Sonar Survey conducted within Gulf of Farallones, 1989, by the U.S. Geological Survey

In 1989, the U.S. Geological Survey (USGS) began a major geologic and oceanographic investigation of the Gulf of the Farallones continental shelf system, designed to evaluate and monitor human impacts on the marine environment (Karl and others, 2002). The study region is located off the central California coast, adjacent to San Francisco Bay and encompasses the Gulf of the Farallones National Marine Sanctuary. Geologic mapping of this area included the use of various remote sensing and sampling techniques such as sub-bottom profiling, sidescan-sonar and bathymetric mapping, gravity core and grab sampling, and photography. These data were used to define the surficial sediment distribution, underlying structure and sea floor morphology of the study area.
The primary focus of this report is to present a georeferenced, digital sidescan-sonar mosaic of the study region. The sidescan-sonar data were acquired with the AMS-120 (120kHz) sidescan-sonar system during USGS cruise F9-89-NC. The dataset covers approximately 1000 km² of the continental shelf between Point Reyes, California and Half Moon Bay, California, extending west to the continental shelf break near the Farallon Islands. The sidescan-sonar mosaic displays a heterogenous sea-floor environment, containing outcropping rock, ripples, dunes, lineations and depressions, as well as flat, featureless sea floor (Karl and others, 2002). These data, along with sub-bottom interpretation and ground truth data define the geologic framework of the region. The sidescan-sonar mosaic can be used with supplemental remote sensing and sampling data as a base for future research, helping to define the local current regime and predominant sediment transport directions and forcing conditions within the Gulf of Farallones.

1989年，美国地质调查局（U.S. Geological Survey, USGS）启动了针对法拉隆湾大陆架系统的重大地质与海洋学调查项目，旨在评估并监测人类活动对海洋环境的影响（Karl等，2002）。该研究区域位于加利福尼亚州中部海岸外，毗邻旧金山湾，范围涵盖法拉隆湾国家海洋保护区。本次区域地质测绘采用了多种遥感与采样技术，包括次表层剖面测量、侧扫声呐（sidescan-sonar）与水深测绘、重力岩芯采样、抓斗采样以及摄影成像。上述数据被用于明确研究区域的表层沉积物分布、地下构造与海底地貌形态。
本报告的核心目标是呈现研究区域的地理参考数字化侧扫声呐镶嵌图。本次侧扫声呐数据由AMS-120（120kHz）侧扫声呐系统，在美国地质调查局F9-89-NC航次中采集完成。本数据集覆盖了加利福尼亚州雷耶斯角与半月湾之间约1000平方千米的大陆架海域，向西延伸至法拉隆群岛附近的大陆架坡折处。该侧扫声呐镶嵌图展现了具有异质性的海底环境，包含露头岩石、沙纹、沙丘、线性构造与凹陷，以及平坦无特征的海底（Karl等，2002）。上述数据结合次表层解译结果与实地验证数据，共同界定了该区域的地质框架。该侧扫声呐镶嵌图可与补充的遥感及采样数据配合使用，作为未来研究的基础，助力明确法拉隆湾内的局部流场格局、主要沉积物输运方向及动力条件。