Bathymetric Surveying Overview
What is Bathymetric Surveying?
Bathymetric surveying is a process that scans bodies of water to map their depth and features. Surveyors can use several techniques for this survey but mostly rely on echos, sonar, and doppler systems to provide accurate data.
What Problems It Solves:
Bathymetric surveying is helpful for water quality studies, detecting the contours of streams and reservoirs, and tracking water flow to search for fast and slow spots.
Images of Bathymetric Surveying
Advantages & Disadvantages of Bathymetric Surveying
Bathymetric surveying has a variety of advantages for science, including:
- Viability at many different depths
- Practical applications for marine geology
- The ability to collect data beneath rock layersHelp with administering marine resources.
However, it also has some disadvantages, including:
- Bathymetric surveying is very slow in deep waters
- Ships need to overlap the same area many times for accurate images
- Sensor width narrows in shallow areas
These disadvantages aren’t enough to stop the surveying from being helpful, but the time and cost make it difficult to use outside targeted areas. This may change as scientists develop better tools and techniques for surveying.
Bathymetric Surveying Process
Bathymetric surveying follows a straightforward process.
Step One: Selecting A Boat
The first step is selecting the right boat, or boats, for the survey. A single small boat is often enough for shallower areas. Large regions may require several boats or changing boats based on the specific details of the region.
Step Two: Getting Equipment
Once a survey team knows how many boats they’ll be using, they can start getting the equipment for it. This varies slightly depending on the exact surveying process but usually includes one echosounder for each boat, plus additional tools as needed.
Echosounders are devices that can create and measure sound waves, usually those going straight down. Sound travels about 1500 meters per second underwater, so by measuring how long it takes to return, a ship can measure the exact depth of the area.
Many ships also use GPS systems to get accurate positioning information to help build the map.
Step 3: Planning a Route
Once all the ships are ready, it’s time to plan a route for the survey. Echosounders are relatively small, so accurate surveys require passing each area several times to cover as many places as possible. This is the main reason that bathymetric surveying takes so long.
It’s possible to speed up the survey by using additional boats. This is a good choice if you have the funds for several ships and want to get the information as fast as possible.
Step 4: Calibrating Equipment
Calibrating equipment is essential to getting accurate readings. The best time to calibrate the equipment is after arriving on-site, and many surveyors do this at the same time as planning a route.
Step 5: Deploying Equipment
Equipment should only go onto ships after calibrating it because some checks can be hard to do once it’s on the vessel. Most ships need a bespoke frame to hold the surveying equipment.
Some ships may also get other equipment for additional measurements at the same time. These aren’t strictly necessary for bathymetric surveys, but many people prefer to collect as much data as possible in one run, so it’s more cost-effective.
Step 6: Sound Casting
Sound casting involves testing the measurement speed at one site while the boat is stationary. This may also involve using a rope or another manual measuring tool to verify the accuracy of the readings. This is important because factors like temperature and water salinity can affect the accuracy of the measurements.
Step 7: Running the Survey
At this point, it’s finally possible to run the survey itself. It can take anywhere from a few hours to several weeks, depending on the size of the area you’re checking.
Step 8: Data Verification
After completing the survey, surveyors will check the existing data map to see if any areas need an extra run-through. If so, they’ll get to that area as soon as possible.
Particularly large surveys may have data verification up to several times a day to help minimize the chance of errors and mistakes.
Step 8: Demobilizing
Once the survey is complete, surveyors will power down all tools and equipment, disconnect them, clean the boat and tools, and otherwise help prepare everything for the next project.
Step 9: Data Processing
Meanwhile, experts will use computer software to process all of the data and remove false signals. These can occur for many reasons, such as objects floating in the water, but getting rid of them is generally straightforward.
After data processing, you’ll have the final map, and the survey is complete.
Problems in bathymetric surveying include equipment failure, weather-related delays, and disturbances underwater. Most of these issues are relatively easy to solve over time, so they rarely force an outright cancellation of the survey.
Questions To Ask Contractors
There are a few questions to ask contractors when you’re hiring them for bathymetric surveys, including:
- How long they expect the job to take
- Whether they expect you to provide any particular equipment
- Whether they can provide more teams and equipment
- Whether they can give you samples of previous surveys
Alternative Solutions to Bathymetric Surveying
There aren’t many alternative solutions for bathymetric surveys in deep water, but shallow water has more options.
The primary alternative at depths of 50 meters or less is lidar, a light-based measurement system. This works similarly to the sonar systems, except that it measures light reflection instead of the return of sound waves.
Lidar is more popular in some areas because it disturbs wildlife much less than concentrated sound waves do.
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Bathymetric surveys, compared to lidar:
Bathymetric surveys, compared to lidar:
Costs of Bathymetric Surveying
The costs for bathymetric surveying vary widely, so it’s hard to give an accurate estimate of the costs ahead of time. Factors that go into the cost include the number of hours or days the survey needs, what equipment you’re using, how many people you need to hire, how many boats you’re using, and whether you’re conducting other surveys at the same time.
Realistically, most bathymetric surveys will cost over $6000 per day for a relatively basic scan. You might be able to bring this price down by using different survey techniques for shallow areas, but expect the cost to go up if you need the results quickly.
Frequently Asked Questions
You might not need to do the survey yourself, especially if you’re working in a well-traveled area. There’s a good possibility that the government has already done a bathymetric survey for that area, and if they have, you might be able to use existing maps.
Private contractors may be able to survey within a few days of contacting them. However, if many people request surveys, it could take anywhere from a few weeks to a few months for them to get to your project. Most companies can get to your survey sooner than that, but deadlines frequently change here.
In some areas, you might be able to get surveys done by your local or state government instead. This typically takes a few weeks.
Bathymetric surveys focus on the depth and terrain of water bodies. Hydrographic surveys usually include bathymetric information, water movement data, chemical properties, and other data. Hydrography is more expensive because it needs more equipment, but it also produces much more accurate results.
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