NOS Hydrographic Survey Data

The Bathymetric Attribute Grid (BAG) file is now the standard NOS hydrographic data file for public release. Because BAG files are binary, they can be difficult to use in their native form. NGDC has developed a BAG conversion tool to output data as ASCII (text) xyz files. Empty space in BAG files is not included in xyz output files. Individual files, or an entire survey spanning multiple BAG files can be selected, extracted, processed to xyz format, and zipped for shipment using the new conversion tool. Each conversion also creates an xml metadata file. View an image of the BAG conversion interface.

The National Ocean Service (NOS) Hydrographic Data Base (NOSHDB), maintained by NGDC in conjunction with NOS, provides extensive survey coverage of the coastal waters and Exclusive Economic Zone (EEZ) of the United States and its territories. The NOSHDB contains data digitized from smooth sheets of hydrographic surveys completed between 1851 and 1965, and from survey data acquired digitally on NOS survey vessels since 1965.

Over 76 million soundings from over 6600 surveys are now included in the NOSHDB. These data may be searched and downloaded online using the Hydrographic Survey Data Map Service (an interactive map and data discovery tool at NGDC). The NOSHDB data with search and retrieval software are also available on a DVD-ROM or CD-ROM set.

Data products from NOS surveys, including BAG files, descriptive reports (DRs), smooth sheet images, survey data images, textual gridded data, and sidescan sonar mosaics, are available for download from NGDC using the Hydrographic Survey Data Map Service.

NOS BAG files are gridded, multi-dimensional bathymetric data files, and the current standard NOAA National Ocean Service hydrographic data file for public release. Current versions of the BAG file contain position and depth grid data, as well as position and uncertainty grid data. Additionally, each BAG file contains metadata specific to that BAG file, providing end users information about the source and contents of the BAG file. For additional information please see the open navigation surface file (PDF).

NOS DRs are approved metadata documents relevant to survey level hydrographic data and are available in PDF form. The DR serves as a narrative document that describes the conditions under which the work was performed and discusses various factors affecting the adequacy and accuracy of the results.

NOS smooth sheets are available from NGDC as images in TIFF or SID format. A smooth sheet is the final, neatly drafted, accurate plot of a hydrographic survey using verified or corrected data.

NGDC archives and disseminates over 11,000 smooth sheets and over 8,000 DRs dating from the mid-1800s to the present. The survey data images, gridded data, and sidescan sonar mosaics are available only for recent surveys where high-resolution data was collected.

Related Links:

• NOS Office of Coast Survey (OCS) - home page
• OCS Chart Viewer - view current navigational charts online
• OCS RNCs - obtain navigational charts online
• OCS ENCs - view/download navigational chart layers online