This is unreal and beyond cool. Instead of measuring seismic tremors, it measures, indirectly, the displacement of the ocean surface. Far from the shore, tsunami waves are very long and very low - so they would appear as the whole surface of the ocean going up and down.
That motion pushes air upwards, resulting in a wave reaching high up through the atmosphere, eventually hitting (!) the ionosphere. I didn't even know acoustic waves would propagate through ionised gas!
Finally, this ionosphere disturbance affects GPS signal reception, and can be measured via ground receiver stations.
The upside of this is that it measures, indirectly, motion of the sea, i.e. actual tsunami activity, rather than monitoring directly the potential causes thereof.
To me this is a wonderful example of the power of mathematics and science to go well beyond our normal intuition of how the world around us works works (which was the normal way things were done until only a few hundred years ago).
The fact that we are able to measure things globally indirectly and accurately based on our understanding of physics, hypotheses we make, and then apply those experiments is very cool.
Never mind the marvel of GPS that we've just taken for granted for decades...
I wonder if someone theorized that tsunamis were detectable by this method or whether someone trying to debug these disturbances figured out what they were caused by. Not sure which is more impressive.
Is this how it's measured? Just to see if I got it right:
The atmosphere directly above the tsunami will have a different TEC (total electron count) pattern due to the upward acoustic waves created by the tsunami waves. This patch of atmosphere may or may not be in the line of sight of your many GPS receivers, to some satellite. Those for which it is in the line of sight will show a disturbance. Others won't. You can now cross-compare to "triangulate" where the tsunami waves are.
You've got exactly the right idea, except "cross compare" is underselling it :)
Here's a previous thread on this topic[0].
For each (receiver, satellite) pair, you can calculate the TEC along the signal propagation path by comparing the time of flight of two carrier waves (e.g. L1 and L2)[1].
By fusing the data from each line of sight together you can get a rough, real time, 3D (4D) model of the ionosphere. Then, you have a separate problem of identifying ionospheric anomalies in the model and relating them to phenomena like earthquakes.
As I read the article. The tsunami wave (water) displaces air at the surface and creates a sound wave, and gravity waves, that travels to the upper atmosphere. These waves then interact with electrons in the upper atmosphere.
meanwhile current and former NASA employees are outside, today, protesting damaging budget and employment cuts by the federal government which will end or jeopardize many NASA programs:
The article mentions gravity waves, I thought these were not possible to detect except from massive events like black hole mergers. Am I getting concepts mixed up?
Yup, slight mix-up. Gravity waves are waves in the ocean and atmosphere (or other fluid bodies) where Earth's gravity is the restoring forces that causes wave propagation. Gravitational waves are the waves in spacetime caused by powerful astronomical events like black hole mergers.
Sure, all the water in the ocean is affected by gravity.
However, there are many different types of waves in physics, usually described by some form of wave equation[1]. And for some of those, body forces[2] like gravity doesn't play a direct role.
A relevant example is acoustic waves[3], which are the propagation of changes in pressure. In that case, the only thing gravity is doing is confining the water to a single body through which the acoustic wave can propagate, it doesn't affect the propagation otherwise as such.
I am not 100% sure, but I think the article is referring to gravity waves in a meteorological context, whereby layers of the atmosphere are displaced and "splosh" around on a large scale. This is as opposed to a gravitational wave which is what you are thinking of.
This data augments USGS earthquake data and tsunami simulation data, so it is far better than "fundamental analysis".
I am guessing it will not take long to train a simple neural network to do the job.
The article notes that the tech successfully notified researchers 20 minutes after the initial quake. What the article _doesn’t_ note is how often the researchers get these notifications.
I wonder what the false positive rate is like for this technology.
I don't think we know, yet. The system was only in place a day before the earthquake. The fact that it worked is a nice smoke test, but tells us nothing about false positives nor false negatives.
I'd rather have a false positive than a false negative. In the FP case I have to get to high ground and hang out until there's an all clear. In the false negative I have to run uphill from an advancing wave.
For context: number of earthquakes which potentially may generate tsunamis is measured in hundreds per year across the planet.
Number of potential tsunami events for any given "coast" is measured in single digits per year. In the hottest areas it is tens of events per year.
Right. If the system generates hundreds of alerts per day, and one of them was right one time, that’s not very useful no matter how cautious you want to be.
But it's still preferable to the one that didn't alert you the one time it really needed to.
A test with a high false positive rate can be combined with other tests to give a better picture. A wave detection plus a seismic event is a lot more compelling than either on their own, so long as non-seismic "tsunami" detections and non-tsunami causing seismic events tend to be independent events.
A false negative on the other hand at best might be dismissed if you have enough other evidence, but more than likely will make you stop looking at more data. A zero false negative rate is likely unachievable, and the perfect is the enemy of the good enough, but false negatives are a much worse issue to deal with than false positives.
This is unreal and beyond cool. Instead of measuring seismic tremors, it measures, indirectly, the displacement of the ocean surface. Far from the shore, tsunami waves are very long and very low - so they would appear as the whole surface of the ocean going up and down.
That motion pushes air upwards, resulting in a wave reaching high up through the atmosphere, eventually hitting (!) the ionosphere. I didn't even know acoustic waves would propagate through ionised gas!
Finally, this ionosphere disturbance affects GPS signal reception, and can be measured via ground receiver stations.
The upside of this is that it measures, indirectly, motion of the sea, i.e. actual tsunami activity, rather than monitoring directly the potential causes thereof.
It is crazy to me that it works though!
To me this is a wonderful example of the power of mathematics and science to go well beyond our normal intuition of how the world around us works works (which was the normal way things were done until only a few hundred years ago).
The fact that we are able to measure things globally indirectly and accurately based on our understanding of physics, hypotheses we make, and then apply those experiments is very cool.
Never mind the marvel of GPS that we've just taken for granted for decades...
I wonder if someone theorized that tsunamis were detectable by this method or whether someone trying to debug these disturbances figured out what they were caused by. Not sure which is more impressive.
Is this how it's measured? Just to see if I got it right:
The atmosphere directly above the tsunami will have a different TEC (total electron count) pattern due to the upward acoustic waves created by the tsunami waves. This patch of atmosphere may or may not be in the line of sight of your many GPS receivers, to some satellite. Those for which it is in the line of sight will show a disturbance. Others won't. You can now cross-compare to "triangulate" where the tsunami waves are.
You've got exactly the right idea, except "cross compare" is underselling it :)
Here's a previous thread on this topic[0].
For each (receiver, satellite) pair, you can calculate the TEC along the signal propagation path by comparing the time of flight of two carrier waves (e.g. L1 and L2)[1].
By fusing the data from each line of sight together you can get a rough, real time, 3D (4D) model of the ionosphere. Then, you have a separate problem of identifying ionospheric anomalies in the model and relating them to phenomena like earthquakes.
[0] https://news.ycombinator.com/item?id=42441772 [1] https://news.ycombinator.com/item?id=42471052
As I read the article. The tsunami wave (water) displaces air at the surface and creates a sound wave, and gravity waves, that travels to the upper atmosphere. These waves then interact with electrons in the upper atmosphere.
> and gravity waves, that travels to the upper atmosphere
You spoke correctly. But to further clarify, these are gravity waves, not gravitational waves.
meanwhile current and former NASA employees are outside, today, protesting damaging budget and employment cuts by the federal government which will end or jeopardize many NASA programs:
https://www.space.com/space-exploration/nasa-employees-plan-...
this is the bigger story for the moment
The article mentions gravity waves, I thought these were not possible to detect except from massive events like black hole mergers. Am I getting concepts mixed up?
Yup, slight mix-up. Gravity waves are waves in the ocean and atmosphere (or other fluid bodies) where Earth's gravity is the restoring forces that causes wave propagation. Gravitational waves are the waves in spacetime caused by powerful astronomical events like black hole mergers.
I don't think I understand. Aren't all ocean waves caused by/dependent on gravity?
Sure, all the water in the ocean is affected by gravity.
However, there are many different types of waves in physics, usually described by some form of wave equation[1]. And for some of those, body forces[2] like gravity doesn't play a direct role.
A relevant example is acoustic waves[3], which are the propagation of changes in pressure. In that case, the only thing gravity is doing is confining the water to a single body through which the acoustic wave can propagate, it doesn't affect the propagation otherwise as such.
[1]: https://en.wikipedia.org/wiki/Wave_equation
[2]: https://en.wikipedia.org/wiki/Body_force
[3]: https://en.wikipedia.org/wiki/Acoustic_wave_equation
There are pressure waves in the ocean too.
wind, boats, whales, current interference/interfaces, cthlulu rolling over...
I am not 100% sure, but I think the article is referring to gravity waves in a meteorological context, whereby layers of the atmosphere are displaced and "splosh" around on a large scale. This is as opposed to a gravitational wave which is what you are thinking of.
https://en.wikipedia.org/wiki/Gravity_wave
Near-real-time outputs from GUARDIAN must be interpreted by experts trained to identify the signs of tsunamis.
Hmm. Sort of giving stock market fundamental analysis.
This data augments USGS earthquake data and tsunami simulation data, so it is far better than "fundamental analysis". I am guessing it will not take long to train a simple neural network to do the job.
The article notes that the tech successfully notified researchers 20 minutes after the initial quake. What the article _doesn’t_ note is how often the researchers get these notifications.
I wonder what the false positive rate is like for this technology.
I don't think we know, yet. The system was only in place a day before the earthquake. The fact that it worked is a nice smoke test, but tells us nothing about false positives nor false negatives.
We could know the false positive rate, if it’s been generating a bunch of these alerts but only recently happened to be right.
I'd rather have a false positive than a false negative. In the FP case I have to get to high ground and hang out until there's an all clear. In the false negative I have to run uphill from an advancing wave.
People stop responding to warnings when the false positive rate is high.
For context: number of earthquakes which potentially may generate tsunamis is measured in hundreds per year across the planet. Number of potential tsunami events for any given "coast" is measured in single digits per year. In the hottest areas it is tens of events per year.
Right. If the system generates hundreds of alerts per day, and one of them was right one time, that’s not very useful no matter how cautious you want to be.
But it's still preferable to the one that didn't alert you the one time it really needed to.
A test with a high false positive rate can be combined with other tests to give a better picture. A wave detection plus a seismic event is a lot more compelling than either on their own, so long as non-seismic "tsunami" detections and non-tsunami causing seismic events tend to be independent events.
A false negative on the other hand at best might be dismissed if you have enough other evidence, but more than likely will make you stop looking at more data. A zero false negative rate is likely unachievable, and the perfect is the enemy of the good enough, but false negatives are a much worse issue to deal with than false positives.