Are you looking for a microphone array?

What is the exact goal of your measurements?

If you provide more details I think that I can try to be helpful.

Dear Lucille,

a model of sound propagation in the water and in the air is the same.

The model allows You to make some easy calculation to derive such values

like particles: displacement (x), velocity (v) and acceleration (a). The main assumptions of the model  are : boundlessness of the medium,  propagation of plane wave.

A basic equation is v = p/Z,  where p denotes sound pressure  p ( in Pa)

and acoustic impedance Z = c*r0, where c - sound speed in the medium,

r0 - the medium density.  You can also calculate particles displacement x and acceleration calculating time derivatives v = dx/dt  and  a = dv/dt. For a single frequency (f) these derivatives can be written as  x  = v*2*pi*f,  what implies v = x/(2*pi*f) and a = v*2*pi*f.  

Going back to Your research as far as I remember Your previous post about hydrophones (a voltage drift) You can measure SPL (in dB !!) using these devices. You can recalculate the SPL into Pa and calculate all values You need. If You want to estimate spatial sound distribution what is useful in source (an animal) localization the idea of array processing is probably the best what You can apply.  

I do not know what animals are You going to record but for example  some marine mammals use low frequency sound what justify the assumption of a plane wave.   

If You operate in a field also the medium is "boundless".

     Best regards

        Chris

Hi Daniel and Chris, thanks for your answers.

Daniel, I would like to measure the sound that a swimmer (human) or a fish produces in the water, and more particlularly its particle acceleration.

Chris, thank you very much. It is exactly what I have used so far, by calculating the difference of 2 hydrophones and then estimating the particle acceleration.

I was just wondering if another probe would do the job in a more precise and easy way. I have heard that some vector sensors could do the job (a probe that measure both the particle motion and pressure changes associated with a sound wave), but not sure about them and how to get one.

Thanks again to both of you

Hi Lucille,

please take a look at Microflown offer: www.microflown.com I am quite sure that  they offer  a solution for gas medium and maybe they can have something "out of the box" for You.

        Regards

           Chris

Hi Lucille,

Particle acceleration was tested on some fish species because they lacks hearing specialization. Therefore the hypothesis is that they are sensitive to particle acceleration.

As far as I remember, to measure the particle acceleration, the sensor was located near the fish and required low pressure noise. So I doubt the measure of acceleration as a derivative of the velocity using an AVS (AVISA Microflown's Hydroflown) would give you reliable results.

Have you got interesting news from the commercial company? I heard they have a deidcated pressure-acceleration sensor at APS: http://www.aphysci.com/

Rgds,

Nico

Hi Lucille,

Acoustic vector sensor can provide the information of particle acceleration in three orthogonal axes as well as acoustic pressure in the underwater sound field, and you may purchase a commercial one from Wilcoxon Company if you are interested.

http://www.wilcoxon.com/vi_index.cfm?CatS_ID=41

Regars,

Hongkun

Dear Lucile,

As already mentionned by a couple of people before, some authors compared sound pressure level and particle acceleration level in fishes by using an underwater acoustic pressure-acceleration sensor from APS.

I can advice you to look for paper from Friedrich Ladich lab if you are interested.

Best wishes.

Frédéric.

Dear Lucile, we have published a paper on the Sea Technology of Sept. 2011: Underwater acoustic vector sensor development and application, and there are two types of vector sensors: MEMS and PZT. Generally, they can be used in the range 20Hz to 4 kHz. I hope the information can be helpful.    Best regards, Yuebing  

If I model the acceleration as a = v*2*pi*f (where f is the centroid frequency), then my main concern is no longer the bounds on the velocities estimated. It is the frequency estimation because I assume the diver or the fish is introducing "micro"-Doppler effect.

Have a look at a fish school on ADCP data to be convinced ;).

I know that AVS is the new trend sponsored at ECUA but could someone point us to a good scientific paper (that should be the point on ResearchGate) with directivity index, gain  and bounds on the frequency-dependent DOA estimated instead of commercial articles about the Hydroflown?

Hi Lucille

This reference to a Symposium dedicated to this particular subject is a bit old but may perhaps contain some relevant ideas for your problem?

Acoustic particle velocity sensors: design, performance, and applications : Mystic, CT, September 1995.

http://www.amazon.com/gp/search/ref=sr_adv_b/?search-alias=stripbooks&field-isbn=1563965496

http://scitation.aip.org/content/aip/proceeding/aipcp/368

Sincerely

Claes

So have any of you actually used a triaxial vector sensor?  If so, what product was it?

Hongkun Zhou recommended one of these but the company is not very helpful online and none of my colleagues have any experience of using their equipment   http://www.wilcoxon.com/vi_index.cfm?CatS_ID=41  Any advice?  Thanks Andrew

Have you considered usage of the ADCP (acoustic doppler current profiler)?

I use the Wilcoxon models myself. I've never tried the microflown models. as long as you have good hardware folks to wire them up (by the way, they were bought out by Meggitt a few years ago or so) I've had great luck with them.

Lucille,

just wanted to add one more option. I recently purchased a Passive Acoustic Sensor (PAS) from USSI. its not cheap ($25k with the watertight cables I wanted) but it comes with a nice expert system in matlab and its spent quite a bit of time on wavegliders. you lose your 3rd dimension in elevation, reduced to bearing only. its good from 100 to about 5000 Hz. all on a DC bus and raw feed via Ethernet.

Thank you Cameron! Sounds like what we would need (if more money :)

Some of the Wilcoxon sensors were developed with the US Gov't, and have ITAR restrictions associated with them.  They are not available internationally.  Applied Physical Sciences also has some sensors, but they too have ITAR restrictions.  The Microflown/Hydroflown sensors (from the Netherlands) have never been proven to be effective in underwater applications. 

My recommendation would be to get several good pressure sensors and build your own vector sensor based on pressure gradient measurements.  (I believe that's really what the PAS is.)

Kevin's right on all accounts. That PAS as it was explained to me is COTS.