Vector transmited intensity.
Up to Velocimeters - single point
Dear Benevides,
The output power ref. dB ref μPa@1m is about 171 dB for the Vector.
Please tell me if this isn't the requested number.
The recorded values of received signal and SNR in the Vector is not referenced to this number.
Without knowing your work, I guess the links below is worth a visit.
http://www.nortek-as.com/en/knowledge-center/forum/current-profilers-and-current-meters/579860307?b_start=0#93634216
http://www.nortek-as.com/en/knowledge-center/forum/velocimeters/404672581?b_start=0#866939104
http://www.nortek-as.com/lib/technical-notes/seditments
Best regards
Jonas Røstad
Dear Jonas Rostad
My studies deals with SSC determination by acoustic backscattering. It took me so long to answer because I was performing lab experiments and writing about our line of research. We submit a paper to the JSS which extract is attached, to give you a clearer idea of what we're doing. The open points and questions are underlined in red.
As you can see, we got good quaIitative good results, but I believe to obtain quantitative ones, it is neede to know the parameter I0 (in the Beer's formula), which is the transmitted intensity by the ADV.
I've read in this Forum, that there is a table of transmitted power as a function of the battery charge for the Vectrino. There is a similar table for ADV? Is there anyway to get this parameter?
I'm looking forward for your reply and thanks a lot for your patience and attention
Regards
Benevides Xavier
Dear Jonas Rostad
Continuing this aspect, it's not clear for me how the recorded values of received signal and SNR in the Vector are not referenced to 171dB Intensity level. As the parameter Amp expresses the energy backscattered by all the scatters in the sample volume, shouldn't this value be related to the power transmitted by the ADV in the water?
How is the difference (in db) between High and Low power?
If the noise is constant, the use of high or low power will result in different SNR values and as these values are used to estimate the SSC (linear relation between log(SSC) and log(SNR)), we'd need samples to make calibration curves. But as we're trying to develop a method to avoid making this procedure, it 'd be necessary to know the transmitted intensity by the ADV to use Beer's formula in order to obtain the backscattered energy by all scatters in the sample volume.
Thanks again.
Benevides Xavier
Hi Benevides,
The return signal the Vector is measuring isn't referenced to anything. It's just an internal digital count out of the amplifier circuit. SNR is based on a noise measurement made at the start of each measurement cycle. The Amplitude variable is indeed related to the transmit power since the transmit pulse generates most of the return signal being measured, but we don't do anything to reference the return signal strength to the transmitted signal.
I believe there is a 6 dB drop in power between High and Low power.
I'm not sure what more information we can provide regarding the transmit intensity unfortunately. You might need to measure this for your system?
P.J.
Dear Sir. Rusello,
First of all I'd like to thank for your attention and to apologise for not being clear in my questions.
I understood what you said and what I need to know is the value of Power transmitted (high and low). John Rostad posted previously that the output power ref. dB ref μPa@1m was about 171 dB for the Vector. I 'd like to confirm this value and if this is for High or Low power.
If I'm not wrong this is what is referred as Source Level (SL). Am I right?
Best Regards
Benevides
Dear Sir. Rostad,
I have no words to thank for your quickly answer and attention.
I'll continuing to make some experiments with glass microspheres using the value you gave me to see if we get reasonable quantitative results. Would you mind if I send it to you as soon as they are ready to get your opinion?
Thanks one more and have a nice weekend.
Regards
Benevides Xavier
Dear Sr.
Continuing in this matter, we are conducting a series of experiments with microspheres (from potters) in a tank with about 50l using a 6MHz Nortek ADV, but we are having trouble keeping the mixture homogeneous to get good measurements (we are using 4 aquarium pumps). Mr. Rusello in his work "Acoustic Doppler velocimeter induced acoustic streaming and its implications for measurements", used a glass tank with water mixed with a submersible pump. Is it possible to provide more details on the mechanism of mixing the solution (water + sphericel)?
To study the backscattering by particles of different shapes, we're looking for glass cylinder particles (backscatter by infinit cylinders), in order to repeat the same experiments done with microspheres. It's being a hard work to find it. We are trying to use optics fibers, but the problem is to cut it in small particles. Do you have any idea or any company which produce this kind of materials?
Best Regards
Benevides Xavier
I believe the tank used in those experiments was based on the method in the following paper: http://journals.cambridge.org/action/displayAbstract;jsessionid=91CE0B931315B833754895C9EB1B029F.journals?fromPage=online&aid=1878252
I'm not aware of any suppliers of small cylinders, but I'm sure there is something out there in the industrial coatings world.
P.J.
Dear Sr. Rusello,
As I'm trying to better understanding ADV principles, is there a possibility to give me acess to the paper below, because it's being hard to get it from the net:
Rusello, P. J., A. Lohrmann, E. Siegel, and T. Maddux. "Improvements in acoustic Doppler
velocimetery." Proceedings of the Seventh International Conference on Hy- droscience and
Engineering, Philadelphia, PA, September 2006. Philadelphia: Drexel University, 2006.
Regards
Xavier
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