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Remote Sensing

Fluid Lensing: Seeing through the Ocean’s Surface

What would the ocean look like without any water? With NASA’s up and coming FluidCam, we are able to see what’s going on underwater without even dipping below the surface.

Chirayath, V., Alan, L. (2019) Next-generation optical sensing technologies for exploring ocean worlds—NASA FluidCam, MiDAR, and NeMO-Net. Frontiers in Marine Science. doi: 10.3389/fmars.2019.00521

One of the greatest hurdles in marine science is being able to see what is underwater both efficiently and accurately. On land, you can fly a drone over a savannah and easily identify organisms. But if you fly a drone over the surface of the water, all you will see are blurs. You’d be lucky to differentiate a fish from a piece of algae. Now, with NASA’s fluid lensing technology, we’re able to take clear, centimeter-resolution photos from above the water’s surface, to identify what’s below.

Figure 1. Coral reef in Palau, Source: C. Sartor

Sensitive Ecosystems

Coral reefs are some of the most important marine ecosystems as they support fisheries, protect our coastlines, and even contribute to the air we breathe. We live so close to these sensitive habitats, yet there is still a lot we don’t know about them. Scientists estimate that corals make up about 1% of the ocean floor, but we still don’t know what all of our coral reefs look like. Without this information, it is difficult to protect these dying organisms. If only there was a way to quickly collect data on remote coral reefs.

Technology to the Rescue

About 40 years ago, technology started helping marine scientists view the reefs from afar. With remote sensing, scientists can gather data on marine environments without physically being there. Satellite imagery, for example, allows us to classify different habitats like seagrass beds and coral reefs over large areas. The downside, however, is that you can’t really see details like a species of coral. Luckily, autonomous underwater vehicles (AUVs) were developed. These underwater video cameras are remote controlled and can collect detailed information, like coral species data. Unfortunately, AUVs are expensive and time consuming. There seems to be no ideal technology for studying coral reefs.

So how can scientists collect high quality data from large reef areas? One solution is taking aerial photographs of the water. But if you’ve tried looking through the surface of water to see what’s below, you’ll notice that everything appears blurry. Blurry data is not high-quality data. And you definitely cannot tell what species of coral you’re looking at if it is only a dark blur. Thankfully, Chirayath at NASA has figured out how to correct blurry photographs and identify corals efficiently with a technique called “fluid lensing”.

It’s all a Blur

What creates the blurs? There are a few different things going on: (1) Caustics, or bands of light dance along the surface of the water creating areas you can’t see through; (2) reflections bounce light off water; and (3) refractive lensing magnifies and demagnifies objects under the water. It seems that with all of these light—water interactions, you’d never be able to see what’s under the surface. But, using what they know about caustics, reflections, and refractions, NASA has figured out how to “undo” the blurriness.

Introducing FluidCam!

The FluidCam allows people to take photos from above the water’s surface to see what’s below even if it’s the size of a sardine. The technology simply takes a short video of the water’s surface, runs it through an algorithm, then produces a non-blurry image. It’s as if you are looking at a reef without any water between you and the seafloor. With FluidCam technology, you can even read words on a submerged sheet of paper from above the surface (Figure 2).

Figure 2. First: example photograph with Fluid Lensing, Second: without Fluid Lensing. Source: Wikimedia Commons

NASA has tested the FluidCam in various shallow water environments including American Samoa, Western Australia, and Colorado. The algorithm seems to work in clear water less than 10m deep. They are still working on how to deal with waves and turbidity, but overall, the technology has revolutionized shallow water remote sensing. We can simply fly a FluidCam drone over a coral reef and identify corals down to the genus and even species level. This quick and accurate method will make it easier to study things like how large coral reefs change over time. With FluidCam’s centimeter-resolution images, we may never need to SCUBA dive again!

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