Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities. Hydrography is collected under rules which vary depending on the acceptance authority, traditionally conducted by ships with a sounding line or 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 found within national naval structures. The IHO publishes Standards and Specifications followed by its Member States as well as Memoranda of Understanding, increasingly those charts are provided and used in electronic form unders IHO standards. Governmental entities below the national level conduct or contract for hydrographic surveys for waters within their jurisdictions with both internal and contract assets, 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, commercial entities also conduct large-scale hydrographic and geophysical surveying, particularly in the dredging, marine construction, oil exploration, and drilling industries. Specialized companies exist that haveboth the equipment and expertise to contract with both commercial and governmental entities to perform such surveys, 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, private surveys are also conducted before dredging operations and after these operations are completed. Crowdsourcing also is entering hydrographic surveying, with such as OpenSeaMap, TeamSurv. Apart from obvious cost savings, this gives a continuous survey of an area. Although sometimes accurate to 0.1 -0. 2m, this approach cannot substitute for a systematic survey. Nevertheless, the results are more than adequate for many requirements where high resolution. The history of hydrographic surveying dates almost as far back as that of sailing, in either case, the depths measured had to be read manually and recorded, as did the position of each measurement with regard to mapped reference points as determined by three-point sextant fixes. Single-beam echosounders and fathometers began to service in the 1930s which used sonar to measure the depth beneath a vessel. However, it shared the weakness of earlier methods by lacking depth information for areas in between the strips of sea bottom the vessel sounded, in 1904, wire-drag surveys were introduced into hydrography, and the U. S. Coast and Geodetic Surveys Nicholas H. Heck played a prominent role in developing and perfecting the technique between 1906 and 1916, in the wire-drag method, a wire attached to two ships or boats and set at a certain depth by a system of weights and buoys was dragged between two points. If the wire encountered an obstruction, it would become taut, the location of the V revealed the position of submerged rocks, wrecks, and other obstructions, while the depth at which the wire was set showed the depth at which the obstruction was encountered. This method revolutionized hydrographic surveying, as it allowed a quicker, less laborious, prior to the advent of sidescan sonar, wire-drag surveying was the only method for searching large areas for obstructions and lost vessels and aircraft
A nostalgic 1985 sketch of hydrographic surveying in Alaska.
A U.S. Coast and Geodetic Survey diagram of wire-drag hydrographic survey operations, ca. 1920. The basic principle is to drag a wire attached to two vessels at a set depth; if the wire encounters an obstruction it will come taut and form a "V," indicating the location of an obstruction at that depth.
Graphic depicting NOAA hydrographic survey ship conducting multibeam and side scan sonar operations