How do weather buoys measure wave height?

[Jools_of_Top_Cat]

The principles are understood, the wave height from trough to peak, but how does a buoy fixed to the bottom by chain do this.

GPS is surely not accurate enough for altitude, especially as they measure down to feet.

Is barometric pressure accurate enough?

Is the buoy on a winder which rotates as the buoy rises and falls?

Does anyone know how it is done, I have no motive other than a passing interest after looking at wind sites over the last couple of days....

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>

</A>

 

[kindredspirit]

They have a heave sensor (whatever that is!)

Details here

<A target="_blank" HREF=http://www.marine.ie/scientific+services/data+services/data+buoy/faq.htm>Picture of heave sensor here.</A>


<hr width=100% size=1><A target="_blank" HREF=http://www.begleys.com/weather.htm>Useful links for Irish waters.</A>

 

[rich]

Thanks,allways wondered how they worked.

<hr width=100% size=1>http://www.jersey-harbours.com

 

[Jools_of_Top_Cat]

Thank you for that, interesting site by the way, will come back to that one.

A heave sensor I found, appears to be a very accurate sonar, makes sense I guess. Found a document here for anyone interested.

<A target="_blank" HREF=http://www.vttss.com/pdf/hs50.pdf>http://www.vttss.com/pdf/hs50.pdf</A>

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>

</A>

 

[kindredspirit]

Wow! 5 cm accuracy. that's some accuracy.



.

<hr width=100% size=1><A target="_blank" HREF=http://www.begleys.com/weather.htm>Useful links for Irish waters.</A>

 

[longjohnsilver]

Can't open the link re the heave sensor, but for some reason I always thort the buoys measured from sea level to peak, thus only half the height of the actual wave.

Have I been labouring under a misconception for all these years?

<hr width=100% size=1>

 

[Jools_of_Top_Cat]

After further reading I think you are right. It appears from limited information I can find the heave sensor can be used to compensate a sonar for accurate surveying. It is not as I first assumed a sonar in itself.

On its own it appears to as you suggest measure the waves by using the raw data that would otherwise be fed to the computer to carry out the compensation calculations. They are used it seems on cranes and other marine applications where compensation for sea movements is essential.

here is a better explaination <A target="_blank" HREF=http://www.aanderaa.com/docs/Wave_Height_3595_D232.pdf>http://www.aanderaa.com/docs/Wave_Height_3595_D232.pdf</A>

extract >> The sensor is mounted on a buoy that will follow the
movement of the waves. The accelerometer, mounted on the
pendulum senses the movement of the buoy.
The accelerometer´s sensitive axis is kept vertical, plus or
minus the pendulum’s displacement angle. Since the accelerometer
also senses gravity, the variation of the maximum
acceleration measured during the pendulum´s oscillation
period is a measure of the vertical acceleration caused by
the waves.
The acceleration is sampled four times a second and then integrated
twice to give the vertical distance the accelerometer
has traveled. This is the distance from the top to the bottom of
a wave. The output from the sensor is the significant wave
height which is the average height of the upper third of all
waves during the measuring interval and wave periode. The
measuring interval, typically every 10 minutes, is determined by
the Sensor Scanning Unit 2800 placed in the buoy
superstructure. The outputs are two 10-bit digital words



<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>

</A>

 

[kindredspirit]

<A target="_blank" HREF=http://www.marine.ie/scientific+services/data+services/data+buoy/faq/waveheightandperiod.htm>Link above doesn't seem to work so here it is again.</A>




.

<hr width=100% size=1><A target="_blank" HREF=http://www.begleys.com/weather.htm>Useful links for Irish waters.</A>

 

[Born_Free]

Heave Sensor? Oh yeah, SWMBO's got one of those, but those new wrist bands seem to have fixed it!
Sorry guys, couldn't resist that one.

<hr width=100% size=1>Born Free!
Now I'm expensive