Can LiDAR Penetrate Water?

One question we often encounter from our clients and technology enthusiasts alike is: can LiDAR penetrate water? It’s a question that not only peels back the layers on the functionality of LiDAR but also brings to the surface its potential in uncharted territories such as underwater exploration and marine archaeology.

As UK’s experts in drone LiDAR surveys, we’re excited to dive into this intriguing subject matter, shedding light on how far LiDAR can reach beneath the water’s surface and under what conditions.

This blog post will guide you through wether LiDAR can penetrate water.

Can LiDAR Penetrate Water?

LiDAR can penetrate water, but its effectiveness depends on various factors such as water clarity, turbidity, temperature, salinity, and depth. Green light with a wavelength of 532 nm is used in underwater LiDAR systems, also known as bathymetric surveys, as it penetrates water most effectively. These systems can probe ocean depths up to 300 meter. However, the accuracy of LiDAR measurements can be affected by light absorption, refraction, water clarity, and surface roughness, among other factors.

How does LiDAR technology work underwater?

The main principle of LiDAR involves sending a light signal and timing how long it takes for that light to bounce back to the sensor. From this, we can determine the distance between the sensor and the object.

However, the aquatic environment poses some challenges. Light behaves differently in water compared to air – it gets absorbed and refracted, or bent. Because of this, we can’t use just any kind of light. It turns out that green light (with a wavelength of 532 nm) can penetrate water most effectively, making it the preferred choice for underwater LiDAR systems.

This is referred to as “bathymetric surveys,” which is essentially LiDAR technology adapted for underwater topography mapping.

The range of this technology is impressive – it can probe ocean depths up to 300 meters.

A recent advancement in the field is the use of single-photon detection.

This is a very sensitive method of detecting light which allows for real-time imaging of moving targets underwater. This has many practical applications, such as inspecting underwater structures (like oil platforms), archaeological surveying of submerged sites, and even uses in defense and security.

limitations of underwater LiDAR measurements

LiDAR technology is instrumental in mapping the seafloor and studying underwater environments. However, like any technology, it comes with its own set of challenges and limitations.

1. Light absorption and refraction: Light doesn’t always travel straight in water. It can lose power and get bent, which is known as refraction. This bending can make the data we get from LiDAR less accurate.
2. Turbidity: This is just a fancy word for how clear the water is. If there are lots of tiny particles floating around in the water, it can block the LiDAR signal. This prevents it from reaching the bottom and making accurate measurements.
3. Temperature and salinity: The warmth and saltiness of the water can also impact LiDAR readings. Depending on these two factors, the LiDAR depth measurements can be off by around 4-6mm.
4. Depth limitations: LiDAR can map the seafloor up to a depth of about 300 meters. Beyond this, it starts to lose its effectiveness.
5. Weather conditions: Believe it or not, the weather can impact underwater LiDAR too. Conditions like fog and rain can limit how well the LiDAR laser beams penetrate and reflect, affecting the quality of the data.
6. Power loss: The deeper the laser goes underwater, the more power it loses. This loss of power can also influence the accuracy of the measurements.

Despite these challenges, LiDAR is still a very useful tool for creating maps of underwater landscapes and understanding coastal environments. Scientists and engineers are always working on new ways to get around these issues. For example, they might try using different colors of light, or tweaking the power and frequency of the light pulses.

Water Clarity’s Impact on LiDAR Penetration

Water clarity significantly affects LiDAR’s ability to penetrate water and obtain accurate underwater measurements. The penetration of LiDAR in water depends on factors such as turbidity, presence of suspended particles, and vegetation.

Here’s how different water types can affect LiDAR’s performance:

In summary, water clarity plays a crucial role in LiDAR’s ability to penetrate water and obtain accurate underwater measurements. Clear water allows for better penetration and more accurate data, while turbid water and water with vegetation can hinder LiDAR’s performance and reduce the accuracy of the measurements.

maximum depth LiDAR water penetration

The depth that a LiDAR system can measure is greatly affected by the clarity of the water. The clearer the water, the further the LiDAR system’s laser pulses can penetrate, and thus the deeper it can measure.

In clear water, a LiDAR system can measure up to about 300 meters deep. This is because the light from the laser can penetrate deep into the water before it gets absorbed or scattered.

On the other hand, when the water is turbid, or cloudy, the LiDAR system’s laser pulses cannot penetrate very far because the particles in the water scatter and absorb the light. This prevents the light from reaching deeper parts of the water. In these conditions, the LiDAR can only measure up to about 3 meters deep.

To give you a better idea, here’s a table that shows the maximum depth range of LiDAR in different water clarity conditions:

Please note that these depth ranges are approximations, as the actual depth range of LiDAR can be influenced by several other factors, including the power and wavelength of the laser used, as well as the type and concentration of particles in the water. So, the ability of LiDAR to measure depth in a water body is largely influenced by the clarity of the water. The clearer the water, the deeper LiDAR can measure, and the cloudier or more turbid the water, the shallower the LiDAR’s depth range becomes.

Water Surface Roughness and LiDAR Measurements

When the surface of the water is rough, like on a windy day when there are lots of waves, it can scatter the LiDAR light pulses in many different directions. This scattering makes it hard for the LiDAR system to determine the exact distance from the sensor to the bottom of the water body, which can lead to inaccuracies in the measurements.

Here are some specific ways that water surface roughness can impact LiDAR measurements:

Reflection and refraction

Rough water surfaces can cause the laser light to be reflected or refracted. This means that the light can bounce off in different directions or get bent as it passes from the air into the water. Both of these effects can lead to errors in the detected underwater depth and position measurements.

Signal attenuation

The roughness of the water surface can also affect the strength of the LiDAR signal. When the surface is rough, it can weaken the signal that returns to the sensor. This weakening, known as signal attenuation, can potentially reduce the accuracy of the measurements.

Impact on water surface detection

For LiDAR systems used for underwater mapping, called bathymetric LiDAR systems, detecting the water surface is a crucial first step. The system needs to know exactly where the water surface is to accurately determine how much the light beam will bend as it enters the water (this bending is due to a phenomenon known as refraction). However, a rough water surface can make it harder to accurately detect the surface, which can then lead to errors in the depth measurements.

Challenges in shallow water

In very shallow water, the effects of surface roughness can be even more pronounced. This is because the light doesn’t have to travel as far, so any disturbances at the surface can have a bigger impact on the accuracy of the measurements.

Despite these challenges, researchers are always looking for new ways to account for water surface roughness and improve the accuracy of LiDAR measurements in different water conditions. So while water surface roughness can indeed make it harder to get accurate depth measurements with LiDAR, scientists and engineers are continually working on ways to overcome this issue.

Conclusion

In conclusion, LiDAR technology has proven to be a valuable tool for underwater exploration and marine archaeology, despite its limitations and challenges.

Factors such as water clarity, turbidity, temperature, salinity, and depth can affect the accuracy of LiDAR measurements, but ongoing research and development continue to improve the technology’s capabilities.

As experts in drone survey and using LiDAR, we are excited to witness the advancements in this field and the potential for uncovering unseen underwater landscapes and historical sites. By understanding the limitations and working to overcome them, we can continue to push the boundaries of LiDAR technology and its applications in the aquatic environment.