Would Ultrasonic Sensor Detect Seawater?

Thread Starter

Hafidz Abdurrafi

Joined Feb 7, 2019
3
Hello, I have a question about frequencies.

I am currently working on a project, in which I'm trying to detect incoming waves of the sea.

First thing comes to mind was to use the ultrasonic sensor, but would it be possible? Would it's 20kHz frequency detect Seawater, or should I use a different frequency.

If it's not possible to use the sensor, I might have to design a new sensor altogether, but I don't know at what frequency Seawater reflects the radiowaves.

Sorry if I made any mistake, first time posting in this forum.
 

Thread Starter

Hafidz Abdurrafi

Joined Feb 7, 2019
3
What’s wrong with a float, like a buoy? In other words, what are you really trying to do?
Well, ultimately I'm trying to detect tsunami waves as warning system, but at this point just normal sea waves from a distance would suffice for the prototype. A buoy would work, though I'm hoping I could do it from the shore (but that means I have to use another transmitter antenna for greater distance).

I might have to design the antenna, it seems, even from a buoy. Warnings have to be as early as possible, after all.

Ultrasonic waves are not radiowaves, they are soundwaves.
And I would expect seawater to reflect them, the same as freshwater.
I see, then 20KHz it is. Though I wonder how I could increase the transmission distance.

What characteristic of the wave are you trying to detect? Height? Arrival time? Temp? Etc?
Assuming this is the smallest tsunami wave, that would mean 10 meters tall, I don't know much about everything else though.
 

Thread Starter

Hafidz Abdurrafi

Joined Feb 7, 2019
3
How big a wave? What constitutes a "wave" versus "not a wave".
At least 10 meters tall, to trigger the sensor that there is something out there in the sea.

Could lidar work at a relevant range? I assume you’d like to see the wave some distance away, like 1000 yards or more?
Yes, I would like that. Sadly I don't know much about lidar, and haven't had the chance to work with them.

On the other hand, more reading material, yay. I'll be sure to check it out.

Wouldn't an accurate sea floor map be the first information needed to predict a tsunami? Then simulations from different directions.
I'm not sure about that, but you might be right.

Though the only thing I knew of predicting the disaster is through the seismograph indirectly. If there's an earthquake over there, there might be a tsunami over there as well, especially if it's on the ocean.
 

BR-549

Joined Sep 22, 2013
4,938
By the time you detect it with line of site means.........it's too late. Not all of them come with a wave front....some creep up....it depends on the bottom and direction.
 

WBahn

Joined Mar 31, 2012
26,326
At least 10 meters tall, to trigger the sensor that there is something out there in the sea.



Yes, I would like that. Sadly I don't know much about lidar, and haven't had the chance to work with them.

On the other hand, more reading material, yay. I'll be sure to check it out.



I'm not sure about that, but you might be right.

Though the only thing I knew of predicting the disaster is through the seismograph indirectly. If there's an earthquake over there, there might be a tsunami over there as well, especially if it's on the ocean.
It sounds like you first step needs to be doing some basic research into the phenomenon you are trying to detect.

To be of any use, how far out do you have to detect this wave? I don't know how fast they travel in shallow water, but I know in deep water they are commonly 500 mph. But even at 50 mph, 1000 yards is covered in 40 seconds.

How are you planning on using an ultrasonic sensor to detect such a wave? In air, I think that ultrasonic detection of objects at even 100 m is very difficult and very expensive. I could be wrong -- this isn't my area of expertise by any means. If the transducer is located underwater, how are you planning to detect the wave?
 

drc_567

Joined Dec 29, 2008
926
https://en.m.wikipedia.org/wiki/Schlieren_imaging

... There is an optical technique that allows differing fluid densities, as in fluid or gas, to be distinctly observed ... Typically, a shadow of a pressure waveform will be produced in a manner that can be observed or photographed. This technique is sensitive and is sometimes used to see dynamic air pressure patterns created by fast moving objects, such as projectiles when they exit a weapon. However, it may be possible to fashion a means of observing the characteristic pattern of the Tsunami waves some distance from shore, before they reach shallow water. Some sort of pneumatic cylinder might be able to simulate a rapidly moving hydraulic wave so that the image could be specifically identified. Ideally, there would be a distinct pattern difference between ordinary ocean waves and those of a Tsunami nature, due to different densities. This would require further investigation.
 

ericgibbs

Joined Jan 29, 2010
11,172
hi HA
Where are you planning to mount the ultrasonic sensor, so that it measures the wave height relative to the sea surface.??

I used submersed differential pressure sensors to measure tidal and wave height and energy.

The connecting cable between the surface equipment and the sensor included a hollow air pipe, this is so that one face of the sensor was at the ambient air pressure. So the sensor measured the actual water depth pressure.

Your problem for tsunami detection is that any distance from the shore in deep water, the change in water is hardly detectable from the background swell.
It is only in the shallower shore water where the wave height increases, then it will be to late to warn and evacuate.

Look at the research being done on satellite sea level measurement.

E
BTW: some older quay wall mounted tidal height measurement systems used ultrasonics, 150kHz or 200kHz where common,
 

LesJones

Joined Jan 8, 2017
2,731
Would change in altitude (Or rate of change of altitude.) given by a GPS receiver on the buoy not do what you want ? If you used an ultrasonic sensor on land pointing down at the water the warning would be too late.

Les.
 

AlbertHall

Joined Jun 4, 2014
10,581
Is the incoming tsunami wave always preceded by the retreat of the sea?
If so, then detecting the retreat would give the longest warning time an the problem becomes detecting lack of sea.
 

atferrari

Joined Jan 6, 2004
4,122
Your problem for tsunami detection is that any distance from the shore in deep water, the change in water is hardly detectable from the background swell.
It is only in the shallower shore water where the wave height increases, then it will be to late to warn and evacuate.
I think this is the real main point.

It is surprising to see how a train of friendly smooth waves in open sea, that you hardly notice when on board your vessel, do change abruptly near shore.

That is why abnormal waves, as along South African coast could take you in surprise because the mechanism that generates them is somewhat different. Luckily seen very few of them not too close nor too big.
 
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