Editing Hydrographic survey (section)

==Modern integrated hydrographic surveying==
[[File:Sonar operations by survey ship.jpg|thumb|Graphic depicting NOAA hydrographic survey ship conducting multibeam and side scan sonar operations]]

In suitable shallow-water areas [[lidar]] (light detection and ranging) may be used.<ref Name=nhsptxt>{{Cite web |url=http://www.nauticalcharts.noaa.gov/hsd/docs/NHSP_2009_TextOnly.pdf |title=NOAA Hydrographic Survey Priorities 2009 Edition}}{{dead link|date=January 2023}}</ref> Equipment can be installed on inflatable craft, such as [[Zodiac Group#Zodiac Boat|Zodiacs]], small craft, [[autonomous underwater vehicle]]s (AUVs), [[unmanned underwater vehicle]]s (UUVs), Remote Operated Vehicles (ROV) or large ships, and can include sidescan, single-beam and multibeam equipment.<ref>{{Cite web |url=http://chartmaker.ncd.noaa.gov/hsd/wrecks.htm |title=Office of Coast Survey - Side Scan and Multibeam Sonar |publisher=[[National Oceanic and Atmospheric Administration]] |date=August 8, 2006 |archive-url=https://web.archive.org/web/20070209015914/http://chartmaker.ncd.noaa.gov/hsd/wrecks.htm |archive-date=February 9, 2007 |url-status=dead}}</ref>  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, but increasingly, with the aid of improved collection techniques and computer processing, the data is collected under one standard and extracted for 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 intended for the data (for example, [[navigation chart]]s, [[Digital Terrain Model]], volume calculation for [[dredging]], [[topography]], or [[bathymetry]]) this data must be thinned out.{{clarify|Thinned out?|date=January 2023}} It must also be corrected for errors (i.e., bad soundings,) and for the effects of [[tides]], [[Heave (translational motion)|heave]], [[water level]]<ref>{{Cite web |first1=Gretchen |last1=Imahori |first2=W. Michael |last2=Gibson |first3=Kristen |last3=Tronvig |date=February 11, 2003 |id=Draft |publisher=[[National Ocean Service]], [[NOAA]] |url=http://www.thsoa.org/hy03/3a_3.pdf |title=Improvements to Water Level Reducers for Hydrographic Surveys in Hydrodynamically Complex Tidal Regimes |archive-url=https://web.archive.org/web/20070325091416/http://www.thsoa.org/hy03/3a_3.pdf |archive-date=March 25, 2007 |url-status=dead}}</ref><ref>{{Cite web |url=http://chl.erdc.usace.army.mil/library/publications/chetn/pdf/cetn-vi-17.pdf |title=Heave Compensation For Hydrographic Surveying |work=Coastal Engineering Technical Note |volume=VI |number=17 |date=March 1985 |publisher=U.S. Army Engineer Waterways Experiment Station, Coastal Engineering Research Center |location=Vicksburg, Mississippi |archive-url=https://web.archive.org/web/20070614123051/http://chl.erdc.usace.army.mil/library/publications/chetn/pdf/cetn-vi-17.pdf |archive-date=June 14, 2007 |url-status=dead}}</ref><ref>{{Cite journal |url=http://www.hydrographicsociety.org/Articles/journal/2002/104-3.htm |title=Measuring Water Level Corrections (WLC) Using RTK GPS |first1=Brad |last1=Scarfe |number=104 |date=April 2002  |journal=The Hydrographic Journal |archive-url=https://web.archive.org/web/20070324014031/http://www.hydrographicsociety.org/Articles/journal/2002/104-3.htm |archive-date=March 24, 2007 |url-status=dead}}</ref> [[salinity]] and [[thermocline]]s (water temperature differences) as the velocity of sound varies  with temperature and salinity and affects accuracy. Usually the surveyor has additional data collection equipment on site to measure and record the data required for correcting the soundings. The final output of charts can be created with a combination of specialty charting software or a [[computer-aided design]] (CAD) package, usually [[Autocad]].{{citation needed|reason=ref for usually Autocad|date=January 2023}}

Although the accuracy of crowd-sourced surveying can rarely reach the standards of traditional methods, the [[algorithm]]s used rely on a high data density to produce final results that are more accurate than single measurements. A comparison of crowd-sourced surveys with multibeam surveys indicates an accuracy of crowd-sourced surveys of around plus or minus 0.1 to 0.2 meter (about 4 to 8 inches).{{citation needed|date=January 2023}}