One of the fundamental challenges of the modern-day Construction industry has to do with effectively understanding the soil’s water content of proposed sites. This is particularly essential in areas where pioneer structures are being built, especially offshore. One of such department which continues to seek a more effective solution in this regard in the UAE is Dredging. Thankfully, bathymetric surveys seem to be that ever-elusive solution.

Definition of Bathymetric Survey

Bathymetric Survey for Dredging

According to Wikipedia, “Bathymetry is the study of underwater depth of ocean floors or lake floors.” It is used to precisely ascertain the underwater topography of a body of water. This implies that for an in-depth understanding of soil water content, and underwater topography, Bathymetry in the form of a Bathymetric survey is required. A Bathymetric survey  – also known as Hydrographic survey – involves mapping out the shape and how deep a terrain underwater is to describe the land that lies below.

This survey uses different kinds of acoustic sounding equipment to measure the depth of a body of water by making sound waves bounce from a transducer (which is a device that performs both functions of transmitting and receiving). The transducer is usually fixed on a ship or a boat, which sends sound energy to the seabed and then back to the transducer which acts as a receiver. The energy received is then converted into electrical signals decoded to standardized marine nomenclature.

The Bathymetric survey has become quite an indispensable tool to industries such as the construction & oil industries especially as it concerns the laying of offshore pipes and facilitating offshore rigs. It is also extremely useful in examining environmental impacts. Other areas of importance include dredging companies, construction, and survey companies all over the world. Countries with a focus on eye-catching infrastructure development utilize this type of survey. A typical example of such a country would be the United Arab Emirates as it enables them to:

  • Collect data to ascertain the amount of soil that needs to be removed or dug up from the sea/lake for dredging and capital projects.
  • To check if the required depth has been achieved after the dredging exercise has been executed.
  • Thanks to the GPS and echo sounder equipped with bathymetric equipment, they can be monitored safely.
  • Since the operators control bathymetric equipment from the water bank, the risks of conducting a bathymetric survey are drastically mitigated.
  • It makes work simple and fast
  • It is versatile

Currently, the UAE is creatively transforming seashores into innovative lands such as the Palm Jumeirah and Saadiyat Island projects. This means that bathymetric surveys are of utmost importance to decision-makers as they must ascertain the soil’s water content, especially in areas where they wish to build upon. The stakeholders must also check the amount of soil that needs to be removed from the particular area they wish to transform. This helps to understand how proposed structures may react to expected environmental conditions given the data collected during the bathymetric survey.

How is a Bathymetric survey conducted using drones?

The drones work with an echo sounder, also known as SONAR, which is an acronym for Sound, Navigation, and Ranging. It is used to measure distance and how much time it takes for an acoustic signal made from the bottom of the sea or by a suspended sea element.

Drone payload for Bathymetric Survey

The drone payload is made up of the:

  1. Transducer or probe which is located under the surface. Its job is to convert electrical signals to sound waves and sound waves to electrical signals. This means that the transducer can serve as a receiver and transmitter at any required time.
  2. The other part of the device is the echo sounder, which is a box that collects electrical impulses sent from the transducer, which is then transmitted in images to be displayed to the operator.

The transducer is one of the centerpieces of the device because it plays a major role by emitting ultrasound towards the ocean floor. It may be likened to a bat in this regard. These signals are sent to the sounder to calculate the obstacle’s distance judging from the sent signal’s speed and the time taken to hit the ocean floor.

The SONAR can be a single beam or multi-beam, depending on the criteria. The single-beam echo sounder is categorized into:

  • The mono-frequency echo sounder, which provides the depth (or distance from the SONAR which is latched under the vessel, to the ocean floor) for a given position.
  • The bi-frequency echo sounder provides two depths. One of these depths is the sedimentary deposit, and the other is at the bottom of the lake.

The multi-beam echo sounder has a multi-frequency echo sounder that gives a more precise water depth at different points.

Bathymetric survey of a lake using UAV drone with echosounder

What does the output of a Bathymetric survey look like?

The output of a bathymetric survey typically includes data in four sections: These sections represent data from the sonar analysis, Lidar system, the joint bathymetric dataset, and an analysis of the bathymetric changes over a specified period.

The first section illustrates the data accumulated by the sonar system.

data accumulated by the sonar system

 

The second section illustrates the data accumulated by the Lidar system.

data accumulated by the Lidar system

The third section illustrates the joint bathymetric dataset that used both sonar and Lidar data. Both descriptions of data contain an analysis of survey errors.

joint bathymetric dataset of sonar and Lidar data

The final section contains the analysis of the bathymetric changes over a long term period and short term period.

analysis of the bathymetric changes

Collectively, these sections provide an in-depth analysis of changes over time, the current state of the seafloor in relation to measurements from Lidar and Sonar measurements. This is done to minimize the error margin to acceptable standards.

How is bathymetric surveys using drones compared to traditional techniques?

The traditional bathymetric survey techniques date back to early history when long slender poles were used as sounding poles. Deeper soundings were taken by attaching a weight to the line. As time went on, the techniques improved to mechanical sounding devices using copper wire to replace the ropes. These copper wires were an improvement as they reduced the tendencies of the breakage of the lines.

Later, a sounding machine made from pianoforte wire was invented for better sounding. Many other inventions followed until scientists discovered that sound could be heard in the water, and echo-sounding systems began to be invented.

These traditional techniques were used until several inventions led to the introduction of drones in bathymetric surveys.

Add to this, Bathymetric survey drones are unique as it doesn’t require direct involvement of workers in the field as other traditional techniques might require. This reduces the likelihood of injuries, which is almost nonexistent if necessary guidelines and protocols are observed.

There is very little limitation in using Bathymetric survey drones as this can cover more ground in a short period and produce the desired accurate results.

Unlike traditional bathymetric techniques, Bathymetric survey drones are cost-effective.

A case study conducted research on the use of echo sounding, which consumes time and demands lots of funds as it requires making measurements from a ship in deep waters or a small vessel in shallow waters. Also, detailed surveys in coastal regimes would require considerable time and effort to cover a small portion of the seabed.

Compared to traditional techniques, drones are more efficient, give more accurate data, and are faster, safer, and reliable.

Even though the depths that were measured were accurate, they were mostly limited in amount. Most times, information supposedly sought for within the soundings was missing since the traditional method did not allow the mariners to view the water’s bottom features. This meant that they were mostly unable to calculate or ascertain the depth of the body of water for safe navigation.

Conclusion

aerial drone survey

The use of drones for the bathymetric survey has been of great benefit owing to an ability to drastically mitigate the risks of direct human interference. Drone technology also enables one to see the exact and current hydrographic information and monitor the change or evolution of terrain.

Bathymetric drones also operate very well in harsh environments due to a built-in resistance to strong wind from storms and saltwater.

Due to advancements in technology, the drones can also fly for a longer period, which means wider coverage over a short period.

Bathymetric survey drones can serve as a solution when traditional bathymetric survey methods cannot be implemented. When an Unmanned surface vessel (USV) is not available, bathymetric survey drones can fly. This means that they can provide more data from the top view on illustrating or mapping out the land located on the seafloor.

As a result of these numerous advantages of the bathymetric survey drones, they are quickly taking over the maritime industry and becoming a constant feature there.

GeoDrones is a leading provider of this technology in the UAE. Using drones, GeoDrones has collected and visualized up-to-date and highly accurate data that is valuable throughout different stages of any infrastructure project.

For a more effective, flexible, and affordable Bathymetric survey, choose GeoDrones.