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Science that is just the ‘tip of the iceberg’

8 mins read

This week, I published my first journal article about iceberg scattering.

In the bigger context, studying the physical behaviour of icebergs is important.

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To get a better picture, this would require ground truthing. In science, ground truthing refers to on-location collection of data and information.

The problem is that getting to these remote sites is very expensive and very treacherous given the nature of icebergs.

Ever heard of the phrase ‘tip of the iceberg’? We still don’t really know a large amount about the part of an iceberg that is emerged underwater.

We only know the top 10% that is visible above the ocean surface.

Only 10% of an iceberg is shown above the surface. Source: LiveScience

A quick scientific fact for you. The reason only 10% shows above the surface is due to the change in density between ice and seawater.

Seawater density is about 1025 kg/m3, whilst ice is 920 kg/m3.

You can try a quick experiment in which you just place an ice cube into a glass of water or other drink. What you’re seeing is a buoyancy effect.

This drink has a higher density than the ice cubes and the fruit slice. Photo by Isabella Mendes on Pexels.com

As an object with a smaller weight hits the water, it will fully submerge for a split second whilst a buoyancy force then upthrusts it back to the surface.

The object will settle at a point in which the water weight is the same as the object, creating equilibrium.

You might be thinking, why don’t ships sink if their weight is greater? This is because the hull encloses a volume of air, creating a shape which is less dense than water.

In my paper, I didn’t look at buoyancy or density that much. Instead, I focused on geophysical properties such as shape, and size of the icebergs.

You see, icebergs can be classified based on these properties. Smaller icebergs are called growlers, and bergy bits.

Yes, they really are called that.

The smaller icebergs are growlers or bergy bits. Photo by Frederik Sørensen on Pexels.com

Then as icebergs get larger, the classification becomes boring- medium, large, and very large.

From the pictures, you might be wondering why some icebergs appear bluer than others.

Blue icebergs have had every air bubbles squeezed out by compressed snow which make them denser. White ice still has air bubbles within it.

The shape is of interest too. In Antarctica, flat topped icebergs are a tabular shape, formed from the calving of flat topped ice shelves.

In contrast, Arctic icebergs calve from glaciers, so you might get more irregular shapes like blocky, dome, drydock, spire, wedge and pinnacle.

A third point of interest is surface wetness. This basically means the top of an iceberg may have surface liquid water on it.

Finally, a fourth point of interest in iceberg properties is its dielectric constant. This is basically the measure of the iceberg’s ability to insulate electric charges.

And now we have the basic physics of icebergs, we come on to the main aim of the study I published.

To address this aim, we need to know what method we’ll use. In remote sensing, a common type of radar used to detect or analyse icebergs and ships is synthetic aperture radar (SAR).

ALOS-2 satellite, containing a SAR system. Source: JAXA

We use SAR due to its capability to transmit and receive waves in remote areas where there is little to no sun or a large cloud cover. A SAR system also uses the Doppler effect to measure distances on the ground.

If you ever wondered why sirens sound higher pitched when approaching you, and lower pitched after they pass, this is due to the Doppler effect. SAR works in the same way.

The siren from an emergency service vehicle will always have a higher pitch and frequency as it is approaching you. Photo by Pixabay on Pexels.com

Before the SAR passes over the object, the Doppler frequency of the beam that it receives is higher. After it passes over, the frequency of the beam decreases.

You can read more about SAR in the paper. Let’s talk about what makes it useful for iceberg studies such as my own.

SAR can be used to detect icebergs on the ground, and send them to ships for safe and secure shipping. But there is a limitation to the size of the icebergs that current SAR systems can detect.

And due to climate change, an abundance of much smaller icebergs smaller in size than which the radar can detect, could create huge hazards for ships.

For this reason, we are in the process of creating iceberg detectors using coding programs and higher resolution data to try to address this.

What SAR can do is study physical behaviour of icebergs from above. It does this through polarisation, which I already touched on briefly.

The science of polarisation of waves is known as polarimetry and there are three types of polarimetric mode. There is a brief introduction to polarimetry in the paper.

How about some more practical knowledge from my study?

We’re almost there. We just need to touch on one more theoretical aspect:  the scattering.

In radar, the term backscatter refers to a wave which has hit a target, but scatters in a different direction. This is happening constantly with icebergs due to the geophysical properties I mentioned above.

There are four main types of scattering (surface, volume, double bounce, helix) all of which are covered in my paper.

Studying the scattering behaviour of icebergs using a quad-polarimetric SAR system was the main aim of my study. Our results give hope for providing some better iceberg classifications for the future.

Studying this further will reveal that scattering types and parameters are all induced by the geophysical nature of icebergs, as my paper shows.

The next work is focused on testing previous iceberg detectors, and eventually innovating a brand new one from scratch.

If you have questions on icebergs, polarisation of waves, or radar, you are welcome to get in touch. My journal article is available for free here.

Feature image source: Pexels

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