While the purposes for land and marine elevation surveys are similar (e.g., national defense, finding routes of passage, resource exploration, engineering applications, etc.), the surveys are carried out independently of one another and mutually stop at the shoreline. Despite this division, integration of the results of the two types of surveys is of increasing interest. Population growth in the US has been fastest in the coastal states where many of the country's largest cities and most popular recreational beaches are located. With this growth have come a variety of new environmental pressures such as over development of beaches and wetlands, contamination of estuaries, increased economic costs associated with storm damage and flooding, dredging, oil and gas exploration/production, and over fishing to name but a few.
These environmental pressures are prompting federal, state and local government agencies to be increasingly pro-active in sustaining the robust and attractive environment of the US coastal zone-- defined here as extending from the coastal states out to the country's 200-mile offshore limit. These agencies are attempting to manage growth within the coastal zone and its usage through a variety of means, one of the most important being Geographic and Land Information Systems. Coastal planners are using these systems to map out future land development, mitigate pollution, prepare for emergencies due to natural hazards, monitor environmental change within the coastal zone over time, and assess offshore resources.
A fundamental database for such GIS/LIS applications is gridded elevations, upon which digital maps of rivers, infrastructure and other geographic information can be overlain. While digital elevation models (DEMs) of the coastal states are available through the US Geological Survey (USGS), until now there has been no comparable product for offshore elevations aside from custom grids generated by individual investigators. The National Geophysical Data Center is taking advantage of both an extensive national hydrographic database and the maturation of software for constructing, managing, viewing and accessing gridded geophysical data, to assemble a new, gridded data base of coastal zone elevations that complements and enhances the USGS 3-arc-second DEMs. This database, which merges the hydrographic soundings with the USGS/NIMA DEMs in a common grid format, will provide the first comprehensive view of the US Coastal Zone; one that extends from the coastal states across the shoreline into water depths as deep as the hydrographic data will support a continuous view of the seafloor.
The gridded database will encompass the coastal zone of the continental US, Alaska, Hawaii and Puerto Rico. The US coastal zone is being gridded in sections due to the immense volume of data involved in this project. In this paper, we describe how the database is being assembled. We also describe the novel software we have developed for accessing the database, which greatly facilitates the selection and preparation of an elevation grid for importation into GIS/LIS applications.