Hydrographic Surveying Overview
What is Hydrographic Surveying?
When you order something online from out of the country, it probably travels overseas via either a plane or a ship. More than half of the goods transported overseas to the United States come by ship. Safe and reliable marine transportation requires information about not only the surface of the sea but also the terrain below the surface that we can’t see.
Hydrographic surveying is the process of using special sonar and light detection equipment to map the physical features beneath a body of water. This includes the seafloor, ocean depth, records of tidal patterns, and coastal obstacles. This data gets converted into hydrographic models, which help ships navigate obstacles below the water’s surface.
What Problems It Solves:
A hydrographic survey is chiefly a preventative measure when building on a shoreline location or establishing a route for shipping transport. Hiring a surveyor will ensure that the site is suitable before you pour time and money into a shipping route or a dock, dam, or harbor.
Hydrographic survey operations provide nautical maps that ship navigators can use to travel over bodies of water safely. Not only do these data contain information about the subterranean geography, but also the water levels and the tides.
Accurate information about the tides and the water levels is essential when navigating vessels in and out of a port. Sometimes the boat’s bottom can be very close to the seafloor when approaching the shore, and accurate readings of the tides and the underwater geography are crucial to keep from running aground.
Hydrographic surveys are also helpful for responding to disasters like hurricanes. Surveyors investigate changes in depth that may have resulted from the disaster, as well as any debris that may have fallen into the water and changed the depth of a certain point.
Images of Hydrographic Surveying
Advantages & Disadvantages of Hydrographic Surveying
Benefits of hydrographic surveying include:
- Safer navigation for ships such as navy vessels and shipping transports.
- Routes mapped out for relief vessels for quicker aid in emergencies.
- Knowledgeable construction of dams, ports, and docks.
- Environmental preservation and protection.
The hydrographic surveying operation has its drawbacks, however:
- Multibeam echo sounders require specific software to analyze the data.
- Doesn’t work very well in shallow water since the beams cover more area at greater depths.
Hydrographic Surveying Process
When you need to perform a hydrographic survey, it’s best to use a contractor or a surveying service. These professionals have training and education in surveying marine geography. A Hydrographic Surveyor typically works for a private mapping service, though sometimes governments hire surveyors for surveying projects on a state or local level.
Once hired, the contractor will survey the requested area, probably using a small vessel and some sort of sonar.
Get Equipment and a Boat
Most hydrographic surveys require only a small boat. The equipment used to conduct the survey includes an echo sounder and other equipment. An echo sounder sends soundwaves down into the water directly below and measures the time it takes for the sound to return to the boat. In this way, the echosounder measures the depth of a body of water.
Collect Data Using Survey Equipment
Because their main job is data gathering in the field, hydrographic surveyors spend much of their time aboard survey vessels, sometimes in unfavorable weather conditions. A survey may take anywhere from a few hours to several weeks, depending on the size of the area.
After collecting data in the field, surveyors convert the data into final soundings about where the surveyors gathered the data.
Create Nautical Charts and Maps
Once the survey is complete and the data processed, you will have the information you need to safely begin your project. The Office of Coastal Surveys is constantly updating the National Oceanic and Atmospheric Administration’s (NOAA) database of nautical charts, and updates to these maps incorporate data collected during hydrographic surveys.
Hydrographic surveyors require specialized equipment when collecting data in the field.
- Multibeam echo sounder/ multibeam sonar
- Side-scan sonar
- Light detection and ranging technology (LIDAR)
- Laser scanners
- Conductivity, temperature, and depth unit (CTD)
- Global positioning system (GPS)
- Tide gauges
Is permitting necessary for a hydrographic survey? A surveying contractor will likely conduct your survey, and their work should meet the standards set by the International Hydrographic Organization.
The IHO is an organization that supports safe navigation for marine vessels and the preservation of the marine environment. They are involved in what hydrographic offices are doing internationally, ensuring that charts and maps are accurate, developing new methods and technologies for safely and efficiently surveying marine geography.
The IHO upholds standards for hydrographic surveys, the charts created using hydrographic data, and the competency of hydrographic surveyors and cartographers.
Common problems during a hydrographic survey are usually caused by the environment, whether that be in the water itself or the form of inclement weather. Surveyors are used to working in bad weather, but sometimes the elements can disrupt the survey. Another common problem during surveys is equipment failure. Stopping for repairs causes delays.
Questions To Ask Contractors
When hiring a contractor to perform a hydrographic survey, there are several questions you should ask them before hiring them:
- How much the survey will cost.
- How long the survey will take.
- What kind of equipment do they have/ how many boats and team members are available.
Different Types of Hydrographic Surveying
- Harbor Survey: This type of survey maps out harbors, ports, and the surrounding underwater terrain. This ensures that ships can navigate safely into port.
- Coastal Survey: This survey gathers data about offshore geography and sediments.
- Passage Survey: This type of survey involves mapping out major sea lanes, keeping hydrographic maps up to date.
- Correction Survey: This survey measures water depth and underwater geographical features after a man-made change to the area, such as dredging.
- Wreckage Survey: this survey is used to gather data on the position of wreckage underwater.
Alternative Solutions to Hydrographic Surveying
An alternative solution to hydrographic surveying is a bathymetric survey, which depicts details of underwater geography and is more effective in deep water.
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Hydrographic surveying, compared to bathymetric surveying;
Hydrographic surveying, compared to bathymetric surveying;
Costs of Hydrographic Surveying
The cost of hydrographic survey service is difficult to estimate ahead of time since it will depend on various factors, including:
- Hours or days spent surveying.
- Equipment used.
- Location of the survey.
- Distance traveled/size of the area surveyed.
- Surveyors hired.
Bid & Buying Solicitation
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Frequently Asked Questions
If your area is already frequently traveled, surveys of that area may have been federally or locally funded. In this case, you can use the charts that already exist.
A bathymetric survey is cheaper because it only records depths and submarine geography. A hydrographic survey also includes information about the tides and the water’s chemical makeup and is more expensive because of its detail and accuracy.
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