Editing Hydrographic survey (section)

===Wire-drag surveying===
{{split section|Wire-drag hydrographic surveying|date=January 2023}}

In 1904, wire-drag surveys were introduced into hydrography, and the [[United States Coast and Geodetic Survey]]′s [[Nicholas H. Heck]] played a prominent role in developing and perfecting the technique between 1906 and 1916.<ref>{{cite web|url=http://www.history.noaa.gov/cgsbios/bioh14.html|title=NOAA History – Profiles in Time/C&GS Biographies – Captain Nicholas H. Heck|website=www.history.noaa.gov}}</ref> 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 and form a "V" shape. 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.<ref name="noaahistorysurvey"/> This method revolutionized hydrographic surveying, as it allowed a quicker, less laborious, and far more complete survey of an area than did the use of lead lines and sounding poles. From a navigational safety point of view, a wire-drag survey would not miss a hazard to navigation that  projected above the drag wire depth.
<gallery heights= 300px widths=300px>
Wire drag operations.jpg|Wire-drag hydrographic survey operations (diagram),<br />[[United States Coast and Geodetic Survey|U.S. Coast and Geodetic Survey]], ca. 1920.
Grunnslep fra 1932.jpg|Principle of sea surveying with two boats,<br />Norwegian Sea Survey, 1932.
Grunnslep fra 1930.jpg|Technical details of tools used,<br />Norwegian Sea Survey, 1930.
</gallery>

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.<ref name="heck">{{cite web|url=http://www.history.noaa.gov/ships/heck.html|title=NOAA History – Tools of the Trade/Ships/C&GS Ships/HECK|website=www.history.noaa.gov}}</ref> Between 1906 and 1916, Heck expanded the capability of wire-drag systems from a relatively limited area to sweeps covering channels {{convert|2|to|3|nmi}} in width.<ref name=NOAA200WireDrag>{{cite web|url=http://celebrating200years.noaa.gov/breakthroughs/hydro_survey/welcome.html#techni|title=Breakthrough article on Hydrographic Survey Techniques|first=US Department of Commerce, National Oceanic and Atmospheric|last=Administration|website=celebrating200years.noaa.gov}}</ref> The wire-drag technique was a major contribution to hydrographic surveying during much of the rest of the 20th century. So valuable was wire-drag surveying in the United States that for decades the U.S. Coast and Geodetic Survey, and later the National Oceanic and Atmospheric Administration, fielded a pair of [[sister ship]]s of identical design specifically to work together on such surveys. [[USC&GS Marindin|USC&GS ''Marindin'']] and [[USC&GS Ogden|USC&GS ''Ogden'']] conducted wire-drag surveys together from 1919 to 1942, [[USC&GS Hilgard (ASV 82)|USC&GS ''Hilgard'' (ASV 82)]] and [[USC&GS Wainwright (ASV 83)|USC&GS ''Wainwright'' (ASV 83)]] took over from 1942 to 1967, and USC&GS ''Rude'' (ASV 90) (later [[NOAAS Rude (S 590)|NOAAS ''Rude'' (S 590)]]) and USC&GS ''Heck'' (ASV 91) (later [[NOAAS Heck (S 591)|NOAAS ''Heck'' (S 591)]]) worked together on wire-drag operations from 1967.<ref name="noaahistorysurvey"/><ref name="heck"/><ref>{{cite web|url=http://www.history.noaa.gov/ships/marindin.html|title=NOAA History – Tools of the Trade/Ships/C&GS Ships/MARINDIN|website=www.history.noaa.gov}}</ref><ref>{{cite web|url=http://www.history.noaa.gov/ships/ogden.html|title=NOAA History – Tools of the Trade/Ships/C&GS Ships/OGDEN|website=www.history.noaa.gov}}</ref><ref>{{cite web|url=http://www.history.noaa.gov/ships/hilgard.html|title=NOAA History – Tools of the Trade/Ships/C&GS Ships/HILGARD|website=www.history.noaa.gov}}</ref><ref name="rude">{{cite web|url=http://www.history.noaa.gov/ships/rude.html|title=NOAA History – Tools of the Trade/Ships/C&GS Ships/RUDE|website=www.history.noaa.gov}}</ref>

The rise of new electronic technologies – sidescan sonar and multibeam swath systems – in the 1950s, 1960s and 1970s eventually made the wire-drag system obsolete. Sidescan sonar could create images of underwater obstructions with the same fidelity as [[aerial photography]], while multibeam systems could generate depth data for 100 percent of the bottom in a surveyed area. These technologies allowed a single vessel to do what wire-drag surveying required two vessels to do, and wire-drag surveys finally came to an end in the early 1990s.<ref name="noaahistorysurvey"/><ref name=NOAA200WireDrag/> Vessels were freed from working together on wire-drag surveys, and in the U.S. [[National Oceanic and Atmospheric Administration]] (NOAA), for example, ''Rude'' and ''Heck'' operated independently in their later years.<ref name="heck"/><ref name="rude"/>