From Ocean Teacher Library

Hydrographic Measurements

Contents 1 Background 2 Hydrographic Agencies 3 Hydrographic Surveys 4 Bathymetric Surveys 5 Additional Resources 6 Subsections of this Article 7 Information about this article 8 Contact

Background

• This very brief description is not intended to provide fundamental instruction in hydrography; as with all OceanTeacher materials, we leave basic marine education to the colleges and universities. This article merely provides a conceptual framework and terminology for data managers who may have a slightly different specific background, but who have marine data responsibilities.
• "Hydrography focuses on the measurement of physical characteristics of waters and marginal land. In the generalized usage, "hydrography" pertains to measurement and description of any waters. With that usage oceanography and limnology are subsets of hydrography. In specialized usage the term applies to those measurements and descriptions of navigable waters necessary for safe navigation of vessels." [From Wikipedia: Hydrography (see below)]
• The term is used by marine scientists not only for marine work related to navigation, but is also a common term for basic hydrochemistry measurements, such as salinity, temperature and oxygen, so there is a little confusion about the proper use of the term. In the sense that all oceanography comes from hydrography), however, it is not an erroneous application of the term.

Hydrographic Agencies

Hydrographic surveys are carried out -- and their products are published by -- many national and one international hydrographic offices (HO):

• Wikipedia: Hydrographic office - Good overview of the services of HO's and specific descriptions of 14 major national agencies
• Wikipedia: International Hydrographic Organization (IHO) - Located in Monaco, this agency coordinats hydrographic activities and products globally. Its work includes the Wikipedia: General Bathymetric Chart of the Oceans (GEBCO), which is available both as master paper charts and in digital form.

Hydrographic Surveys

The following features can be surveyed, located, assessed or otherwise characterized under the rubric of "hydrographic surveys" and subsequently synthesized into various chart, book or pamphlet formats:

• Navigation depths
• Rocks and snags
• Wrecks
• Bottom texture
• Offshore structures
• Coastal features and structures
• Aids to navigation (buoys, signs, lights, structures, etc.)
• Tides - Desirable, but expensive and infrequent
• Currents - Desirable, but expensive and infrequent
• Waves - Desirable, but expensive and infrequent

The products of hydrographic surveys are primarily nautical charts (either hard-copy or electronic in format)

• Wikipedia: Nautical chart
• Wikipedia: Electronic navigation chart

Bathymetric Surveys

Bathymetric surveys are more detailed, scientifically-oriented studies of the seabed than hydrographic surveys. "...hydrographic charts will usually tend to over represent least depths and ignore the actual submarine topography that will be portrayed on bathymetric charts. The former are the mariner's tools to avoid accident. The latter are best representations of the actual seabed, as in a topographic map, for scientific and other purposes. [From Wikipedia: Hydrography] The aim is portray the seafloor in sufficient detail to learn more about the geological, physical, biological (and sometimes chemical) processes that have formed it and may still obtain, as well as to provide very accurate point-by-point depths for engineering and other technical purposes (e.g. placement of a mooring whose instrument depths must be accurately foreknown).

• Wikipedia: Bathymetry
• Bathymetric chart

Additional Resources

• Wikipedia: Hydrography
• Wikipedia: Limnology
• Wikipedia: Oceanography

Subsections of this Article

No subsections available

Information about this article

Short title: Hydrographic Measurements

Description: This article is intended to provide a brief introduction to the types of data and products involved in this discipline. It is not a general introduction to the discipline itself.

Expertise level: beginner

Author: Murray.Brown

Approval status: approved

Approved by: Murray.Brown

Last change: 2009-9-24

Subsection of: Marine Data Concepts

Contact

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