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The measurement and description of the physical features and conditions of navigable waters and adjoining coastal areas, including oceans, rivers, and lakes. It involves geodesy, physical oceanography, marine geology, geophysics, photogrammetry (in coastal areas), remote sensing, and marine cartography. Basic parameters observed during a hydrographic survey are time, geographic position, depth of water, and bottom type. However, observation, analysis, and prediction of tides and currents area are also normally included in order to reduce depth measurements to a common vertical datum. See also Geodesy; Photogrammetry.
A principal objective of hydrography is to provide for safe navigation and protection of the marine environment through the production of up-to-date nautical charts and related publications. In addition, hydrographic data are essential to a multitude of other activities such as global studies, for example, shoreline erosion and sediment transport studies; coastal construction; delimitation of maritime boundaries; environmental protection and pollution control; exploration and exploitation of marine resources, both living and nonliving; and development of marine geographic information systems (GIS). See also Geographic information systems; Navigation.
Modern depth information is achieved with sonar measurements. Dual-frequency echo sounders are used, with a high-frequency, narrow beam to measure the depth below the vessel, and a lower-frequency, wider beam to obtain larger coverage of the terrain. Side-scan sonar, an instrument that transmits acoustic signals obliquely through the water, is normally towed behind the survey vessel and displays the returning echoes via an onboard graphic recorder. Although this technique does not allow exact determination of position and depth (both can be approximated), it provides excellent resolution with a depiction with what lies to either side of the vessel. Multibeam hydrographic survey systems consist of hull-mounted arrays such that a fan-shaped array of sound beams is transmitted perpendicular to the direction of the ship%s track. This provides for the possibility of 100% coverage of the sea floor. See also Echo sounder; Sonar.
Laser airborne systems mounted in fixed-wing aircraft or helicopters are also available for hydrographic surveys. The system emits a two-color laser beam, usually green and red, such that a return is received from the surface of the water by the red laser and from the bottom by the lower-frequency green laser, allowing the depth to be determined from the time difference. They can be operated in depths down to 165 ft (50 m), but more normally to 66 ft (20 m), depending on water clarity. Hydrographers use tide-coordinated aerial photography to delineate the high and low water lines for charting, which in turn is used for base-line determination of offshore boundaries. Satellite positioning of the aircraft using the Global Positioning System with carrier phase measurement and postprocessing of the data provides for determination of the position of the aircraft of the decimeter level. See also Aerial photograph; Laser.
n. the science that deals with the measurements and description of the physical features of the oceans, seas, lakes, rivers, and their adjoining coastal areas, with reference to their use for navigational purposes.
See the Introduction, Abbreviations and Pronunciation for further details.
(DOD, NATO) The science which deals with the measurements and description of the physical features of the oceans, seas, lakes, rivers, and their adjoining coastal areas, with particular reference to their use for navigational purposes.
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
Large scale hydrography is usually undertaken by national or international organizations that sponsor data collection through precise surveys and the publication of charts and descriptive material for navigational purposes. The science of oceanography is, in part, an outgrowth of classical hydrography. In many respects the data are interchangeable, but marine hydrographic data will be particularly directed toward marine navigation and safety of that navigation. Marine resource exploration and exploitation is a significant application of hydrography, principally focussed on the search for hydrocarbons.
Hydrographic measurements will include the tidal, current
and wave information of physical oceanography. They will include bottom measurements, with particular emphasis on those marine geographical features that pose a hazard to
navigation such as rocks,
Hydrography, partly for reasons of safety, tends to be more traditional in outlook and has conventions that are not entirely "scientific" in some views. For example, 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.
A hydrographic survey differs from a bathymetric survey in some important respects, particularly in a bias toward least depths, because of the safety requirements of the former and geomorphologic descriptive requirements of the latter. As just one important example the echosoundings will be conducted under settings biased toward least depths while in bathymetric surveys they will be set for best description of the submarine topographical features that may include sound velocity and slope corrections that are more accurate but eliminate the safety bias.
Hydrography of streams will include information on the stream bed, flows, water quality and surrounding land. Basin or Interior Hydrography pays special attention to rivers and potable water.
Hydrography's origin lies in the making of maps done by geographers in by means drawings and notations made by individual mariners. These were usually the private property, even closely held secrets, of individuals who used them for commercial or military advantage. Eventually organizations, particularly navies, realized the collection of this individualized knowledge and distribution to their members gave an organizational advantage. The next step was to organize members to actively collect information. Thus were born dedicated hydrographic organizations for the collection, organization, publication and distribution of hydrography incorporated into charts and sailing directions.
An interesting historical relationship is that of James Whistler to hydrography. His artistic talents were applied to the sometimes beautiful shore profiles that appeared on charts during his work as a cartographer with both the civilian and naval U. S. hydrographic organizations. Those profiles on early charts were etchings designed to aid mariners in identifying their landfall and harbor approaches.
Hydrographic services in most countries are carried out by specialised hydrographic offices. The international coordination of hydrographic efforts lies with the International Hydrographic Organization.
| Sub-fields of Physical Geography | |
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Biogeography · Climatology & paleoclimatology · Coastal geography · Geomorphology · Glaciology ·
Hydrology & Hydrography · |
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Dansk (Danish)
n. - hydrografi
Nederlands (Dutch)
hydrografie (in kaart brengen van wateren)
Français (French)
n. - hydrographie
Deutsch (German)
n. - Hydrographie, (Gewässerkunde und -beschreibung)
Ελληνική (Greek)
n. - υδρογραφία
Português (Portuguese)
n. - hidrografia (f)
Español (Spanish)
n. - hidrografía
Svenska (Swedish)
n. - hydrografi, sjömätning
中文（简体） (Chinese (Simplified))
水文地理学
中文（繁體） (Chinese (Traditional))
n. - 水文地理學
日本語 (Japanese)
n. - 水路学, 地図上の水路部分
العربيه (Arabic)
(الاسم) الهيدروغرافيا, علم وصف المياه كمياه البحيرات والانهار والبحار
עברית (Hebrew)
n. - מדע סקירת ומיפוי ימים, אגמים וכו', הידרוגרפיה
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Did you mean: hydrography, hydrographic
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| US Military Dictionary. The Oxford Essential Dictionary of the U.S. Military. Copyright © 2001, 2002 by Oxford University Press, Inc. All rights reserved. Read more |
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| Military Dictionary. US Department of Defense Dictionary of Military and Associated Words, 2003. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydrography". Read more |
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