Bathymetric attributed grid
Gridded data formatted as a Bathymetric Attributed Grid (BAG) is a multidimensional hydrographic data file that meets standards developed by the Open Navigation Surface Working Group. Currently, BAG files contain elevation gridded data and Total Propagated Uncertainty (TPU) gridded data, as well as metadata.
Bathymetry Data Index
The Bathymetry Data Index (BDI) is a mosaic dataset that maintains a list of all gridded surfaces registered in the Bathymetry Information System (BIS) geodatabase. The BDI mosaic dataset is a series of tables within the geodatabase that manages the location of gridded bathymetry surfaces on disk. Since the BDI manages the location of gridded surfaces, rather than loading the datasets directly into the geodatabase, file system data storage requirements are greatly reduced. Subsequent surfaces can be generated from the BDI with the use of the Explore Bathymetry and Compose Surface windows. The surfaces created will also be created as a mosaic dataset referencing the same gridded bathymetry surfaces on disk.
Bathymetry is the measurement of underwater depths and the description of landforms beneath a body of water. This information is gathered from 3D and profile analysis of depth data.
A hydrographic survey is the science of measurement and description of water masses, water depths, the nature of the seabed, currents, tides, and other physical features of the ocean. Results from hydrographic surveys are used for navigation safety, ocean and coastal engineering, environmental protection, coastal zone management, marine archaeology, naval operations, and ocean sciences. Typically, hydrographic vessels conduct these surveys using echo sounding equipment; increasingly, surveys include light detection and ranging (lidar) bathymetry from aircraft and sophisticated electronic sensor systems in clear and shallow waters.
Soundings are depth measurements taken from the surface through a water column, generated when a mariner or a machine sends a probe into the ocean. Historically, soundings were taken from simple instruments such as lead lines; today, mariners can collect echo soundings.
The BAG file specification requires an uncertainty grid coincident with depth information. The uncertainty grid is a two-dimensional array of positive values, given in units of meters, that describes the vertical uncertainty at every pixel for which an elevation value is also present.