Bathymetry of Lake Erie and Lake Saint Clair

Bathymetry of Lake Erie and Lake Saint Clair has been compiled as a component of a NOAA project to rescue Great Lakes lake floor geological and geophysical data and make it more accessible. This project is a cooperative effort between investigators at the NOAA National Geophysical Data Center's Marine Geology and Geophysics Division (NGDC/MGG), the NOAA Great Lakes Environmental Research Laboratory (GLERL) and the Canadian Hydrographic Service(CHS). Bathymetric sounding data employed in compiling the one-meter bathymetry (National Geophysical Data Center, 1998) were collected over a 100-year period for purposes of navigation safety and nautical charting by the U. S. Army Corps of Engineers, the NOAA Coast Survey, and the Canadian Hydrographic Service. These bathymetric data, totaling several hundred thousand soundings, are separated four ways in existing archives: by whether they exist in digital form or reside only on paper sheets; and by whether they were collected by the U. S. or Canada. Final assembly of the new bathymetry has resulted from synthesis of bathymetric data from the four sources. Spacing of data control tracklines ranges from 500 to 2500 meters for the open lake and from 125 to 500 meters for nearshore areas. In preparation for bathymetric contouring, digital soundings were converted to metric units and computer plotted in color according to depth range. Contours in metric units were generated directly on overlays from paper sheets and then reduced to compilation scale and patched in. Compilation sheets were scanned and vectorized; and the resulting digital bathymetric contour data constitutes the primary product. The data were hand contoured by geomorphologists to capture and portray the maximum information available, resulting in a degree of detail not attainable with machine contouring and the density of available data. Bathymetric contours were prepared by geologists using sounding data contained in the paper archives at the scale of the survey sheets (scales ranging from 1: 100,000 to 1: 10, 000); or from sounding data contained in digital data bases at standard scales of either 1: 100,000 or 1: 50,000. Details concerning the methods of compilation are given in the western Lake Erie paper (Holcombe, et al., 1997). Bathymetric contours have been spatially reconciled with the NOAA Coast Survey nominal scale 1:80,000 digital vector shoreline, which by definition coincides with the Lake Erie low water datum, the zero-depth employed for bathymetric surveys and nautical charting.伊利湖与圣克莱尔湖水深地形数据（bathymetry）是美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）相关项目的组成部分，该项目旨在抢救五大湖湖底地质与地球物理数据并提升其可获取性。本项目由美国国家海洋和大气管理局国家地球物理数据中心海洋地质与地球物理分部（NGDC/MGG）、美国国家海洋和大气管理局五大湖环境研究实验室（GLERL）以及加拿大水文局（CHS）的研究人员合作开展。 本次1米分辨率水深地形数据所采用的水深测深数据，由美国陆军工程兵团、美国国家海洋和大气管理局海岸调查局以及加拿大水文局为保障航行安全与海图编制工作，历时百余年收集完成。本次整合的水深测深数据总计数十万条，现有档案中其分类方式共有四种：按存储格式分为数字格式与纸质档案两类，按采集方分为美国与加拿大两类。新型水深地形数据的最终整合，正是基于上述四类数据源的水深测深数据合成得到。 开放湖区的数据控制测线间距为500至2500米，近岸区域则为125至500米。为开展水深等值线绘制工作，数字测深数据被转换为公制单位，并根据水深区间通过计算机生成彩色等值线图。纸质档案中的水深等值线则以公制单位直接生成于透明底图之上，随后被缩编至成图比例尺并嵌入整体数据。成图底图经扫描与矢量化处理后，最终生成的数字水深等值线数据即为本次数据集的核心成果。 地貌学家通过人工绘制等值线以充分提取并呈现现有数据中的全部信息，这一方式相较于机器等值线绘制，可依托现有数据密度实现更高的细节精度。地质学家可依托两种数据源绘制水深等值线：一是纸质档案中保存的、测绘比例尺介于1:100000至1:10000之间的测深数据；二是标准比例尺为1:100000或1:50000的数字数据库测深数据。关于数据整合方法的详细说明，可参考《伊利湖西部》相关文献（Holcombe et al., 1997）。 本次水深等值线数据已与美国国家海洋和大气管理局海岸调查局发布的1:80000标称比例尺数字矢量岸线完成空间匹配，该岸线依据定义与伊利湖低水位基准面重合，而该基准面正是水深测量与海图编制所采用的零深度基准。