Sounds of the planet

Remote sensing: using Physics to explore and monitor our environment

Posts By: Philippe Blondel

Killer asteroids or "just passing by"?

📥  Out in space

“Doom!” always makes good headlines, and some British tabloids fretted about the recent passage of an asteroid close to Earth on January 2nd, and the fact it was only detected 6 days before. But what are the actual risks? How often does this happen?? And is anyone doing anything about it?

First, let us look at the numbers. Asteroid 2017 YD7 missed Earth by 1.8 million kilometres, close to 5 times the distance from the Earth to the Moon. So, even if it was within the zone classified as “potentially hazardous” by planetary scientists, its size (between 6 and 21 metres according to NASA) and its trajectory did not make it that much of a threat. Even if it had reached the Earth, the risks would have depended on what it was made of, how fast it travelled and whether it would give a glancing blow or fall vertically. The physics is well known, and you can play around with real impact simulators at http://simulator.down2earth.eu/ and http://purdue.edu/impactearth to assess different scenarios.

Large asteroid impact

University impact, but not as we would want it ... (from a test of simulator.down2earth.eu

Simulating a 100-m wide rock falling on my office at hypersonic velocities, its fragments would destroy the entire campus, creating a crater 331 m deep and a magnitude 6 earthquake. Down the hill in Bath, collapsing buildings would be accompanied with widespread burning. So much for University impact ... But fun aside, it is even likely? After all, the asteroid would need to be large, dense, travelling extremely fast and impacting head on our planet.

How often does this happen? The good news are: “rarely and less and less often”. The number of asteroids impacting planets (and the Earth) has very sharply decreased after the “Late Heavy Bombardment” of several billion years. Most asteroids now are small, at least in potentially Earth-crossing orbits. In 2013, the Chelyabinsk meteor exploded above Russia, creating shock waves that injured around 1,000 people but created little destruction. But what about the others?

Are there “dinosaur-killers” still hurling through space? As they get disturbed by large planets or chaotic interactions with other bodies, are some of them likely to head our way? We know about close to 500,000 asteroids known, most orbiting far away between Mars and Jupiter. Telescope surveys can detect the largest objects, provided they are reflective enough. And common sense would hint that, if they are too small to detect easily, maybe they won’t create as much risk. Still, we want to know where they are, and what they are. This is where radar and radio-telescopes come to the rescue. By reflecting radio waves on asteroids, it is possible to learn about their size, their shape, how they tumble, and get ideas of what they are made of (hard rock or soft grains). And we have strong incentives to map those closer to Earth, as they contain materials useful for future interplanetary flights and mining (in 2016, I participated for example in the first conference between scientists and asteroid miners).

Once we know an asteroid is on its way to Earth, more frequent surveys enable scientists to better understand its trajectory. In most cases, it would disintegrate into the atmosphere, creating “shooting stars” or falling into empty areas (the Chelyabinsk fragments fell into a lake, for example). If it is large enough to be worrying, there are no proven technologies at the moment to destroy it, or even just re-direct it. If there is enough time, putting solar sails on its surface might work. And if not, more aggressive approaches can be used, like kinetic impacts (the joint NASA/ESA mission DART, for Double Asteroid Redirection Test, intends for example to do just that for a test scheduled in 2022).

So there is still work to do. But it is not as bleak as the tabloids would have us believe. And there is very interesting science to do out there in outer space ...

 

Acoustics - From the deep sea to outer space

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📥  From the lab

Asteroids near Earth

"In space, no one can hear you scream" ,,, This was the motto from the first Alien movie and it has been used and abused in the decades since. I lost track of the number of times I have worked on ships and seen T-shirts or posters with "In the deep sea, no one can hear you scream ..." or similar. Although sound travels very well in water (and better than in air) ...

So how would it work in space? Sound does not travel in vacuum, despite what countless movies seem to imply (and yes, I love the sound effects of Star Wars or Farscape, even if I need to leave my scientific mind aside for a time). But space is made of much more than vacuum.

There are planets, first, and some of them are getting increasingly closer as plans for their exploration are firming up. Elon Musk gave a much talked about presentation at the International Astronautical Congress in Mexico last week. I was interviewed on Al Jazeera to talk about the actual feasibility of the scheme, and this still seems rather far off. The exploration of Mars, which needs to take place before any attempt at colonisation, will need to include assessing potential resources in the ground. We know there is water below the surface, from remote sensing by satellites in orbit around Mars. And there are very strong indications that some of this water is still freely flowing at the surface in specific areas. But what about other deposits, for example oxygen? How easy would it be to drill and get it? How stable would exploration platforms, or habitats, be as resources get extracted from below them? Like on Earth, these questions can be answered directly with acoustics. Sending sound waves of different frequencies through the surface, we can listen to their returns and find out how deep they are, and what they are made of. Just like seismics or non-destructive imaging (think about ultrasound scans of human bodies ...)

Planets are great (I love planets) but they are far away, expensive to get to, and with the current state of space exploration programmes, it will be a while before we can get more than passing glances at their marvels and really explore them. Closer to home, though, we have asteroids and comets. They are big pieces of rock or gravel (comets are often compared to "dirty snowballs"). They contain all sorts of minerals and oxygen or frozen water. And they often pass in the neighbourhood. So what about exploring asteroids?

Asteroids near Earth

Asteroids often come to the neighbourhood of Earth. Artist's view from the European Space Agency (Copyright ESA - P.Carril).

This seems much more feasible, and there are actually several companies aiming to mine asteroids for their riches. These companies have been in existence for several years, so they are no "seven-day wonders" but real companies, with serious investors. The government of Luxembourg recently announced it had its own plans to support space exploration and space utilisation. And they organised a great workshop two weeks ago, inviting space industries to meet space scientists. It was a packed programme over two days, with world-famous scientists describing the main discoveries of recent missions to asteroids and comets, and their plans to learn more over the coming years. The ASIME-2016 workshop is now leading to a White Paper, which will lead to recommendations on space mining, the science behind it but also the implications for protection of any possible astro-biology (none found yet, but one can hope ...). I was there to present seismo-acoustics to a different audience, and it was very encouraging to see possible avenues for acoustic exploration of still mostly unknown planetary bodies ...

Once we get to them ... (but at least we have the tools ready ...)

 

 

Finding Nessie … or close enough …

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📥  From the field

The Loch Ness monster is one of the most famous mythical beasts, supposedly lurking below the cold waters of Loch Ness in Scotland. But there has been no conclusive proof of its existence yet, despite many people searching for it over the years … Until …

Looking for animals, even very large, in a long and deep fjord like Loch Ness is like looking for the proverbial needle in a haystack. During a visit to the Loch Ness Monster Museum, long ago, I had seen old sonar records purportedly from “something” lurking in the deep, although my sceptical eye interpreted this as long-range noise in the records … Later, more accurate sonar maps of the bottom of the Loch Ness had revealed structures, more or less circular, build of rocks and rubble and placed at regular intervals. Some journalists of course used the occasion to talk of “monster nests”, but the truth was much more prosaic, if as interesting. As I wrote in my 2009 Handbook of Sidescan Sonar, these structures were associated with the building of the road along the shore. Debris from the construction were loaded onto barges, which dumped everything unceremoniously in the deeper parts of the loch. And, like any collection of objects falling in deep water, these rocks arranged themselves in rough circles.

But this time, even the BBC reported it. So it looked much more serious, and I started reading … This Nessie was a lost prop from a movie several decades ago, not a real, live animal. It was found by my colleagues at Kongsberg Maritime, using a combination of the latest technologies now available: high-resolution sonars, capable of mapping both the topography of the loch’s bottom and its acoustic reflectivity, and the Autonomous Underwater Vehicle MUNIN, their latest model. Their website has a very nice (and short) movie of how they found it. It really is a needle in a haystack!

 

Newborn icebergs - A fresh start to 2015

📥  From the lab

Having fun in the field is one thing. But to have impact, and be really useful, this research also needs to be published. This is where the hard work continues.

Led by Oskar Glowacki, a young and promising glaciologist from Poland, one of our articles was recently published in Geophysical Research Letters, the prestigious journal of the American Geophysical Union. And they liked it so much that it is now featuring on their own blog.

The YouTube video shows examples of glaciers collapsing, and what they sound like underwater. We are meeting in Poland in two weeks to discuss the rest of the analyses, and how we will follow this up, in publications and in the field. Stay tuned 🙂

The Sound of Silence

📥  From the lab

Logo of EC SITAR project

The European SITAR project used sound to detect toxic buried waste at sea. Logo drawn by Peter Dobbins.

Sound is the most useful tool to investigate the world's oceans; it is also used in medical physics, for example for ultrasound scanners. The image above is a nice picture drawn by my colleague and friend Peter Dobbins when he was working with us on the SITAR project, a European collaboration to detect toxic waste buried under the seabed and how risky it was.

But sound is much more than just a tool. It also holds beauty and variety. I was recently invited to write a review for “Sonic Wonderland: a Scientific Odyssey of Sound”, by Trevor Cox. This was a beautiful book, and it invites us to celebrate the richness of sounds all over the world, from home to far away, sometimes below our feet or high up in mountains. More details about the book are available in my review, published by Physics World in its December 2014 issue . This book is a must-read, written by one of the true experts ... And a good gift for the coming festive season too ...

 

30 July 2014 - Return to the Glacier

📥  From the field

Today, we have done most of our work and we even took a short break. For two hours, we went for a walk at the foot of the 500-metre high mountain overlooking the base.  The main purpose was still scientific, looking at Hans Glacier from above and checking the latest signs of calving. There are two autonomous recorders on the bottom at the end of the fjord now: one is still recording noises from the glacier and the icebergs (and the hydrographic vessel, still anchored not far).

On the way, we see flocks of little auks returning from the sea. They are extremely noisy, and it seems there are thousands of birds all shouting at once (there probably are). The ornithologists tell me they nest in the rocks (no twigs here, of course, to build up nests). The auks try to find comfortable holes in the ground, frozen most of the year, and sometimes use burrows 1.5 m long deep. This removes most of the surrounding cold and also the threat of predators.

Talking of predators, we were cautiously avoiding groups of reindeers, napping on the soft, green moss, when a dark speck suddenly reared its head on our path. It was an Arctic fox, who looked at us with increasing interest, then bolted out to go to the closest snow patch.

As it sees us arriving, this Arctic fox scampers away and observes us from afar.

As it sees us arriving, this Arctic fox scampers away and observes us from afar.

We saw fresh reindeer bones that he was gnawing on: no doubt scavenged from further away. The fox comes back as soon as we are at a safe distance, and carries on eating ...

After more walking and climbing on small rocks and different small moraines, we arrive just above the glacier. Still a lot of blue ice at its front, meaning the bottom ice is still being exposed and calves into the sea. There are many blue icebergs drifting away ... Up close, we can see the base of the glacier, and its sides, are eroded and form flanges. A small rivulet of icy water trickles on one side and into the sea ... It's beautiful, and also extremely informative: the base layer of glaciers is usually made of a slush of ice and water, lubricating it so that it can move forward. The surface of the glacier is criss-crossed by crevasses and similar features. Some of the Polar Station's crew regularly take measurements of the glacier's movements, using GPS and markers placed at key points on the ice. A risky business, but they seem very experienced (and very safety-conscious too: I talked with one of them yesterday, and most of his backpack was filled with safety-related equipment).

A different view from our favourite glacier.

A different view from our favourite glacier.

 

28 July 2014 - The bright side of life

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📥  From the field

Polish TV recently showed the farewell concert of Monty Python and "The bright side of life" (my Polish is still extremely limited, but I could understand that much ...) (especially the English part ...) For the last 24 hours, the sun has been shining and I can see its bright rays illuminating the glaciers and moraines on the other side of the bay of Isbjornhamna. Today, we are going to do experiments in the deepest parts of the fjord, and sail there for a large part of the day. We launch our boat shortly after another party of scientists has left for the fjord of  Hans Glacier.  Amongst them is a friend and former Bath postdoc, Aleksandra Kruss. A multibeam sonar expert with an international reputation, she is out there to test the latest generation of high-resolution sonar in this challenging environment. She also kindly agreed to take measurements of the front of the glacier, to help us in our interpretations. She has extensive Arctic field experience so we know she won't get too close to the glacier for safety, but the sonar should do an excellent job at mapping what it looks like underwater.

The bright side of life: this side of Isbjornhamna is graced with a few rays of sunshine ...

The bright side of life: this side of Isbjornhamna is graced with a few rays of sunshine ...

In the meantime, we move to a slightly different type of landscape: very eroded mountains, and much less green. No moss, no lichen visible from the boat: no animals either. The Polar Station has disappeared at the horizon: even finding the peak below which it stands, we cannot see it. The ride to the other side of the bay took us 40 minutes, bumping into the waves on our small Bombard C5. After 20 minutes of measurements, we realise the site is not suitable, and move to a different location, on the original side of the bay (another 40 minutes, bumping into the waves, making sure we fall back into the boat and clinging tightly to the ropes ...). There, we can make the right kind of measurements. We also understand why no one had ever made this before: it's hard, it's cold, and we have to do several trials and use our field knowledge of underwater acoustics before getting it right ...   After many hours drifting in the cold wind and short waves, we have all the results we want and head home. Cold to the bones (it takes me until this evening to warm up, despite the many layers of clothes), but delighted with the results. Which we start analysing immediately after cleaning the equipment, untangling several hundred metres of cables and of course manhandling the boats back on shore (Aleksandra and her colleague are back too: but their boat is fortunately lighter, or maybe it's the fact we are now 5 people hauling it ...)

 

27 July 2014 - Ships passing in the night ...

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📥  From the field

The small icebergs brought to the shore have fallen silent with the evening. The sun is currently hidden behind the 500-metre mountain just behind the base, and the beach is in shadows. What suddenly made these icebergs silent? Curious, of course, we came to investigate after some colleagues told us there was no noise ... (motivated by some aspects of our research, they had combed the beach looking for icebergs with the most bubbles to add to their end-of-work drinks ...) We take measurements in air and in water, and conclude it is a conjunction of the type of icebergs, the contrasts in temperature (or rather the absence: air and water are both close to 1 degree Celsius), and the very calm seas ... We also take some samples to measure in the laboratory ...

Traffic in the Bay of White Bears has increased tonight: there is a large cruise ship at anchor in the deepest part (around 200 m deep), and we can hear the noise of its engines over the several kilometres of water. Another ship (further left in the picture), much smaller, decided to moor very close to where we had deployed an acoustic-recording buoy ... What about the noise it will make, covering what we want to measure over the coming months?

They are Norwegian hydrographers, though, so we do not really begrudge them: they must be doing exciting work too. And we all "comrades-in-arms": we all want to understand more about the polar regions and their climate. Thinking a bit more about it, our first buoy has been there for several months already. The second buoy, 25 metres away, will not start recording until November. So a few hours of engine noise will not really affect our different measurements ...

Ships passing in the night? If only ... One of them has been above our buoy for more than 24 hours now ...

Ships passing in the night? If only ... One of them has been above our buoy for more than 24 hours now ...

 

26 July 2014 – No birds, please …

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📥  From the field

After the last days, we have plenty of field data to analyse and more experiments to run and test different theories. Is the noise coming from the bubbles? From the cracking? What influences how loud it is? Is it the temperature of the air? Of the water? Of the ice itself? Does it depend on how much salt there is in the water? And how does the noise from one iceberg combine with the noise of the others to give what we measure in the field?

This acoustic experiment fits nicely on a table top, and measures the noise of individual growlers as they melt ...

This acoustic experiment fits nicely on a table top, and measures the noise of individual growlers as they melt ... The box on the left contains hydrophones for use in the field, listening to icebergs (or anything underwater) in stereo.

This makes a lot of parameters to investigate. The high-speed photography rig is used fully, day and late into the night, and we have another small tank to run tests in.  The second part of our laboratory is actually in our dormitory: I annexed the desk and put a small aquarium on top. The hydrophone measuring the sound close to melting ice is connected to different bits of kit, and everything is recorded on my computer for later analyses. Melting full growlers in different conditions requires as little background noise as possible. This is not always possible in the local conditions: the station was built to be a polar base, not an underwater acoustics lab, and it is mounted on stilts (to separate from the snow and cold permafrost, in winter). This means that people walking in the corridor outside make the floor move. Doors closing too fast because of the wind do not help. But the main culprits are outside: squabbling geese or cheerful snow buntings settling just below the window.

Snow buntings are the only songbird in Svalbard.  The same size as sparrows, they are a delight to see and hear. But what do they need to sing loudest when the experiments are running :-) ?

Snow buntings are the only songbird in Svalbard. The same size as sparrows, they are a delight to see and hear. But why do they need to sing loudest when the experiments are running?

 

 

25 July 2014 – Fifty shades of blue

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📥  From the field

We do not do as much field work as I expected at the beginning, because of the weather and because we need to do laboratory experiments to check different theories. But today I am happy: the weather is cooperating, and we are away in the field once again.

The glacier has changed over the last days, with more and more blue ice and blue icebergs. Ice from the top of the glacier is white, and becomes blue when it is compressed at the base of the glacier. The front of Hansbreen is gleaming in different shades of blue today, meaning more ice from the base has been exposed and is now melting. There are large blue icebergs all around us.

A typical blue iceberg, calved from the bottom of the glacier. It is around 3 m high above the water: there is 80% more below the water line ...

A typical blue iceberg, calved from the bottom of the glacier. It is around 3 metres above the water line: there is 80% more below ...

The icebergs in the fjord have various shades and various shapes. Some of them are so flat that I would like to step on them (too dangerous to even think about, of course, as their bobbing in the waves reminds us how unstable they are). A Canadian friend sent me the link to a video showing a large iceberg capsizing: very illustrative, even though I prefer watching it with the sound off. Other icebergs look like melting bouncy castles, complete with high towers and oscillations. Some are smudged with grey or brown: remnants from the base of the glacier, gravel or mud taken with the ice as it moves slowly but ineluctably. Sometimes, the icebergs still have huge stones caught into the ice. This one (below) looks a gruyere cheese: the holes were once occupied by round stones, which fell into the water as the ice melted. Closer to the Station, on our way back, some of the icebergs with the most melting behind them look like swans: all white with slender necks …

Gruyere iceberg: the holes had large stones in them, from the bottom of the glacier. This was the base of the iceberg, which has now capsized.

Gruyere iceberg: the holes had large stones in them, from the bottom of the glacier. This was the base of the iceberg, which has now capsized.

During our first deployment of DAB, a little auk swam enquiringly toward us, curious of what we were doing. After seeing it was “just science”, it swam further away, and started ducking its head into the water at regular intervals to find some food.

Once back on shore, late into the night, I have time to glance outside whilst downloading the data from the day. Some sort of eagle is swooping over one of the barnacle goose chicks by the melt pond, and even the parents (usually aggressively protective of their young) do not seem ready to approach. But the chick runs to water … and apparently to safety, as the eagle now flies higher and finally leaves off …