Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration/drilling and related disciplines. 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 synonymously 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.
Hydrography is collected under rules which vary depending on the acceptance authority. Traditionally conducted by vessels and with Echo sounding, surveys are increasingly conducted with the aid of aircraft and sophisticated electronic sensor systems in shallow waters.
Hydrographic offices evolved from naval heritage and are usually found within national naval structures, for example Spain's Instituto Hidrográfico de la Marina. Coordination of those organizations and product standardization is voluntarily joined with the goal of improving hydrography and safe navigation is conducted by the International Hydrographic Organization (IHO). The IHO publishes Standards and Specifications followed by member states as well as Memoranda of Understanding and Co-operative Agreements with hydrographic survey interests.
The product of such hydrography is most often seen on nautical charts published by the national agencies and required by the International Maritime Organization (IMO), the Safety of Life at Sea (SOLAS) and national regulations to be carried on vessels for safety purposes. Increasingly those charts are provided and used in electronic form unders IHO standards.
The United Kingdom has a long hydrographic history officially begun with the 1683 appointment of Captain Grenville Collins as Hydrographer to the King. With the Royal Navy dominating the seas hydrography grew to a worldwide hydrographic activity. That tradition extended to the nations with a common legacy in the Empire, for example, the Australian Hydrographic Service. The British Admiralty Hydrographic Office became the United Kingdom Hydrographic Office which continues the legacy within the Ministry of Defence with responsibility for the Admiralty Charts. The Royal Navy maintains a number of hydrographic survey vessels to continue the work today.
The Argentine Hydrographic Service was established in 1879.
Hydrographic services are provided by the Royal Australian Navy Hydrographic Service.
In United States statutory authority for hydrographic surveys of territorial waters and the Exclusive Economic Zone (EEZ) lies with the National Oceanographic and Atmospheric Administration (NOAA). NOAA hydrographic surveys are conducted by the National Ocean Service, a uniformed corps within NOAA and a fleet of survey vessels based at two major centers. The organic survey assets are supplemented by other agencies and contract surveys in order to survey the large areas within its responsibility. Those were identified in the NOAA Hydrographic Survey Priorities (NHSP) - East Coast alone as being classified as critical. The 2009 status shows out of "Navigationally Significant" were completed. The NOAA Office of Coast Survey, Hydrographic Surveys Division estimates it has awarded approximately $250 million in contracts for hydrographic surveying and related support since 1994.
For inland surface waters such as rivers, streams and inland lakes the U.S. Geological Survey (USGS) has national responsibility. USGS coordinates survey data collection and publishes a National Hydrography Dataset that is designed to be used with geographic information systems (GIS). Other federal agencies such as the Environmental Protection Agency and the U.S. Fish and Wildlife Service use these data and, along with state and local hydrographic collection organizations, contribute to the national hydrographic data base. The Environmental Protection Agency conducts or contracts for surveys on projects such as the GE/Hudson River Super Fund site.
The National Geospatial Intelligence Agency (NGA) oversees charting of international waters for Department of Defense purposes. The Navy's Naval Oceanographic Office conducts many the oceanic surveys. The U.S. Army Corps of Engineers conducts hydrographic surveys supporting its responsibility for the major waterway projects that include navigation and flood control. Hydrographic data from those surveys is published by districts. Such data is incorporated into both NOAA and NGIA products and the Corps engages in efforts to improve hydrographic collection methods. Military combat organizations such as the Navy's SEAL and engineering units have specialized hydrographic reconnaissance survey capability.
The NOAA Office of Coast Survey, Coast Survey Partners web page offers a useful list and summary of major player activities, government and private, with links to those partner web sites.
Governmental entities below national level conduct or contract for hydrographic surveys for waters within their jurisdiction with both internal and contract assets. Such surveys are commonly conducted by or under the standards approved by or the supervision of national organizations, particularly when the use is for the purposes of chart making/distribution or dredging of state controlled waters.
In the United States there is coordination with the National Hydrography Dataset in survey collection and publication. State environmental organizations publish hydrographic data relating to their mission.
Large scale hydrographic and geophysical survey is conducted by commercial entities, particularly in the dredging, marine construction, oil exploration & drilling industries. Industry installing submarine cable for communications or power require detailed surveys of cable routes prior to installation with increased use of acoustic imagery equipment previously found only in military applications. There are specialized companies with both the assets and expertise to contract for such surveys with both commercial and governmental entities. Companies, Universities and investment groups will often fund Hydrographic surveys of public waterways prior to developing areas adjacent those waterways. Survey firms are also contracted to survey in support of design and engineering firms that are under contract for large public projects. Private surveys are also conducted before dredging operations and after these operations are completed. Companies with large private slips, docks or other water front installations have their facilities and the open water near their facilities surveyed regularly.
Modern surveying relies as much on software as hardware. In suitable shallow water areas Light Detection and Ranging (LIDAR) may be used. 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. At one time different data collection methods and standards were used in collecting hydrographic data for maritime safety and for scientific or engineering bathymetric charts. Increasingly with aid of improved collection techniques and computer processing the data is collected under one standard and extracted for the specific use.
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, topography, Bathymetry) 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 (thermoclines.) 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 Autocad.
14 December 2009