Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration/drilling and related diciplines. Strong emphasis is placed on soundings, shorelines, tides, currents, sea floor and submerged obstructions that relate to the previously mentioned activities. The term Hydrography is sometimes used synonomously to describe Maritime Cartography, which in the final stages of the hydrographic process uses the raw data collected through hydrographic survey into information usable by the end user.
HydrographyHydrography focuses on the measurement of physical characteristics of waters and marginal land. Hydrography generally refers to the measurement and description of any waters, and specifically refers to those measurements and descriptions of navigable waters necessary for safe navigation of vessels...
is collected under rules which vary depending on the acceptance authority.
Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration/drilling and related diciplines. Strong emphasis is placed on soundings, shorelines, tides, currents, sea floor and submerged obstructions that relate to the previously mentioned activities. The term Hydrography is sometimes used synonomously to describe Maritime Cartography, which in the final stages of the hydrographic process uses the raw data collected through hydrographic survey into information usable by the end user.
HydrographyHydrography focuses on the measurement of physical characteristics of waters and marginal land. Hydrography generally refers to the measurement and description of any waters, and specifically refers to those measurements and descriptions of navigable waters necessary for safe navigation of vessels...
is collected under rules which vary depending on the acceptance authority. Traditionally conducted by vessels and with
Echo soundingEcho sounding is the technique of using sound pulses directed from the surface or from a submarine vertically down to measure the distance to the bottom by means of sound waves. Echo sounding can also refer to hydroacoustic "echo sounders" defined as active sound in water used to study fish...
, surveys are increasingly conducted with the aid of aircraft and sophisticated electronic sensor systems in shallow waters.
United States Navy SEALSThe United States Navy Sea, Air, and Land Forces, commonly known as the Navy SEALs, are the Special Operations Forces of the United States Navy, employed in direct action and special reconnaissance operations...
and Seabee Underwater Construction Technicians also have the ability to conduct hydrographic surveys. The SEAL/UCT operators are normally called upon before amphibious landings in order to survey the landing beaches.
When surveys are used for the purposes of chart making/distribution or dredging of state controlled waters they are commonly conducted by or under the supervision of national
organizationsA hydrographic office is an organization which is devoted to acquiring and publishing hydrographic information.Historically, the main tasks of hydrographic offices were the conduction of hydrographic surveys and the publication of nautical charts...
. Coordination of those organizations voluntarily joined with the goal of improving hydrography and safe navigation is conducted by the
International Hydrographic OrganizationThe International Hydrographic Organization was originally established in 1921 as the International Hydrographic Bureau . The present name was adopted in 1970 as a result of a revised international agreement among member nations...
. In the United States, hydrographic acceptance is conducted by NOAA for maritime navigation, the Army Corp of Engineers for dredging and marine construction and occasionally the Environmental Protection Agency (on projects such as the GE/Hudson River Super Fund site).
Companies, Universities and investment groups will often fund Hydrographic surveys of public waterways prior to developing areas adjacent those waterways. One example of this would be surveys completed for Riverboat Casinos that ply inland rivers. These large ships require relatively shallow water, but it has to meet minimum depth requirements. Private surveys are also conducted before dredging operations and after these operations are completed. Steel mills and companies that have large private slips and docks have their facilities and open water near their facilities surveyed regularly.
Modern surveying relies as much on software as hardware. Equipment can be installed on inflatable craft, such as Zodiacs, small craft, AUVs (Autonomous Underwater Vehicles), UUVs (Unmanned Underwater Vehicles) or large ships, and can include sidescan, single beam and
multibeam equipment.
After data is collected, it has to undergo post-processing. A massive amount of data is collected during the typical Hydrographic survey, often several soundings per square foot. Depending on the final use (navigation charts, Digital Terrain Model, volume calculation for dredging,
topographyTopography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
,
BathymetryBathymetry is the study of underwater depth of the third dimension of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθυς, deep, and μετρον, measure...
) this data must be thinned out. It must also be error corrected (bad soundings,) and corrected for the effects of tides,
waves/
heave,
water level and water temperature differences (
thermoclineThe thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
s.) Usually the surveyor has additional data collection equipment on site to record the data required for correcting the soundings. Final output of charts can be created in a combination of specialty charting software or a CAD package, usually
AutocadAutoCAD is a CAD software application for 2D and 3D design and drafting, developed and sold by Autodesk, Inc. Initially released in late 1982, AutoCAD was one of the first CAD programs to run on personal computers, and notably the IBM PC...
.
NOAA maintains a massive database of survey results, charts, and data
on the NOAA site.