distance from probe?

Would you please to tell me that how the SSC influences the detection of the bottom of Sontek Vector?  
In my field data, I found that sometimes the Vector can detect the bottom. However,sometimes it would report a zero distance from the probe to the bottom. I want to know the reason of it. Is it affected by SSC? When the SSC is too high, the vector can not detect the bottom, so it will report a zero distance from the probe to the bottom? Can you tell me with what SSC it could work properly

Thank you!

Well, let's hope it is a Nortek Vector...... 

 

 

The SSC will influence the ability of the acoustic signal to distinguish between the bottom and the water.  To simplify things a little, you can think of it as a problem where the reflection from the bottom is constant for a given site whereas the acoustic water return is proportional to the SSC. In order to identify the position the bottom, the bottom scattering must be stronger than the water return.  As the SSC increases this becomes more difficult and at some level the Vector can no longer identify the bottom position.

 

In the latest version of the Vector firmware, we record the acoustic scattering profile at the beginning of every burst.  This allows you to see the data for yourself.  If you work off a complete data set (and not just individual profiles as we do), it is fully possible that you can come up with an algorithm that finds the bottom at times where our software does not   

 

 

Best regards,

 

Atle Lohrmann

Thank you very much.

Would you like to tell me what's the latest version of the Vector firmware which record the acoustic scattering profile at the beginning of every burst? And for the old version, can it be updated with the new version of the Vector firmware.

Thanks again.

Hi there

 

The first version of the Vector firmware that will measure the distance to the bottom at the beginning each burst is version 1.20.  There were a few beta version sent out early in the year but this is the first publically released version.

 

Any Vector can be updated to use version 1.20 . 

   Just go to the support area on our WEB site and download the firmware and the corresponding software.

 

Best regards, Atle Lohrmann

Hi Atle,

Thanks!

Best regards,

dekeete

How can I see the distance to the bottom with version 1.20 if I'm logging continuously?  In the hdr file, I do not see a reference to distance to bottom in either the sen or dat files.

Thanks,

-Jon

 

Dear Jon, I don't think you can.  The distance (i.e. echosounder data) is only collected at the beginning of each burst.

Best regards, Atle Lohrmann

Hi,

I am a new user of vectrino, trying to set the probes at 0.6d from surface water level in laboratory flume. The distance which I see on computer is the location of probe?

 

Thanks

Aakter

 

 

Hi Aakter,

The distance you see is measured from the center transducer to the boundary.

Best regards,

Ketil Horn

Hi,

I have two Vectrinos, one running firmware 1.27+, the other 1.29+. Apart from that the configuration is (as far as I can tell) identical. They are positioned at a similar height from the channel bed in a laboratory flume. The 1.27+ probe gives a distance to boundary of 19.8cm, the 1.29+ probe gives a distance to boundary of 9.7cm (which seems correct).

Could this be a firmware issue, or is there anything else you could suggest that may be causing this?

(BTW, I tried upgrading the firmware on the 1.27+ probe, but it requests a licence key. Any idea where I can find this?).

Thanks,

Mike

Mike Jesson said:

Peter,

Thanks for your response. I've attached a Word document with screenshots showing the distance check and probe checks for both probes.

For both probes the quality indicator is about 900 (875 for the 1.29+ probe, 914 for the 1.27+ probe).

Looking at the probe check data, both are showing a second peak at the 17-19cm mark, and in the case of the 1.27+ probe this is of a similar amplitude to the "real" peak. Presumably this is causing the problem? If so, does this indicate that velocity measurements will also be affected?

Unfortunately I can't attach a picture of the setup. Both are downward facing probes, situated approximately 9cm above the base of a 60cm wide channel, with a smooth plastic channel bed.

Thanks for your help,

Mike

Hi Mike,

It looks like the second peak on the 1.27+ probe is slightly higher on Beam 3 and this is what is throwing the distance check off. It's just searching for the highest peak in this case and unfortunately reporting an erroneous reading.

This won't affect the velocity measurements since the Velocity Range setting in the Configuration window sets the lag between pulses and not the distance to the bed. Just be aware of this problem, think about if the measurement reported by the instrument is believable, and always check your Probe Check plot to verify the distance measurement if it's in doubt. Pretty much anytime I do a  new setup or change anything in an existing one, I examine the Probe Check and make sure everything is okay.

Glad we could identify the problem and good luck taking data!

 

P.J.

Hi Mike,

Just to elaborate on what Peter wrote, this problem is likely to disappear when you upgrade to firmware version 1.29+. We did some significant improvements in version 1.28+ in order to solve problems like this. The problem occurred when the second peak was more distinct than the first one, just like what your probe check data shows.

Best regards,
Sven

Hi Peter and Sven,

Thanks for your help. I've upgraded the firmware and both probes are now showing the distance to channel bed correctly.

Regards,

Mike

just a questions, how come i don't have the distance reading cell

 

by the way, i have just upgraded the firmware to 1.29

 

but still there is no "distance" from the interface

 

my interface only shows

"time

status

temp"

that's all

 

ray

Hi Ray, the distance mode is a feature in the Vectrino + firmware.

Best regards, Atle Lohrmann

Dera Atle

i have double checked again, i do have the firmware 1.29+

is it possible that i am having an older version of software?

 

ray

Dear Ray, you also need to have the Vectrino+ software.  Please see screen dump for what my version (1.09) looks like.

Best regards, Atle Lohrmann

many thanks

now i've upgraded the software as well as the firmware

here is the distance check function, just wondering why the spikes are very large

 

please see attachment

 

thank you very much for your time again

 

ray

Ray,

i am measuring against a acrylic channel wall (bottom wall)

basically, i wan to know what is the limit of the probe. as i actually want to measure velocities very close to the wall, say as close as possible

from the user manual it says, the beams intersect each other 50mm from the transmitter. does it mean that the limit of the probe is 5cm below the transmitter? it means that i can't measure any thing less than 50mm from the transmitter?

 

just need to clarify this

 

many thanks again!

 

ray

Hi Ray,

The Sample Volume is centered 50 mm from the central transducer, but it extends half of the Sample Volume size (as set in the Configuration Window) on either side of this point. For the default Sample Volume size this will be 3.5 mm (default Sample Volume size is 7 mm). Sample Volume size is really the height of the volume since the diameter is set by the transducer's physical dimensions.

For measuring close to the wall I would recommend keeping the Sample Volume center at least 5 mm away from the wall. You can push this limit, but the data may not be of good quality because measuring very near the bed is difficult for any measurement technique. If you want to try measuring closer than this, I would consider changing the Sample Volume size to a smaller value (but avoid using the smallest value of 2 mm) but only after doing some tests to make sure you can measure quality data in an easier region (e.g. away from boundaries).

 

Hope that clarifies everything but let me know if you have more questions.

 

P.J.

yes. this is very helpful indeed

by the way, sometimes, i also have a large amount of negative velocity measurement

are there anything i've done wrongly?

 

ray

 

please see attachment

see the Y velocity is a large negative number

and sometimes my X velocity is negative as well, and they don't fluctuate very much, so they won't go back to positive during the measuring period

 

The data looks very noisy and the SNR is low.  I would suggest that you run the probecheck module in the Vectrino program and compare the data display with the different troubleshooting screens you can find in the manual.

Best regards, Atle Lohrmann

Thanks Atle

just a quick one, are there any ways i can reduce the noise?

 

ray

Dear Ray, you have to do this systematically. First order of the day is to check that the acoustic performance is adequate.  For this, the displays in the manual should provide a good guide.  Please let us know if you stil have questions once you have completed the tests.

Best regards, Atle Lohrmann

Hi Ray,

To expand on what Atle said, move the probe away from the wall so the Sample Volume is at least 1-2 cm from it and run the various diagnostics we've mentioned above to verify the probe is working and you can collect good data. Collect some data in this location and look at it in Matlab or another analysis software to make sure you understand what's going on and believe your measurements. For instance you could make several (4-5 at least) measurements at various distances from the wall and try to fit the mean velocity profile for a turbulent boundary layer. Once your confident making measurements away from boundaries, try to make your measurements close to the wall like you have mentioned.

 

P.J.

thanks PJ and Alte

i've done the probe check, i found there are quite many spikes for bottom echo

i have attached the image please have a look

many thanks

ray

 

 

Hi Ray,

Please look at the Vectrino manual and compare your probe check output to the example given on Page 23 of the most recent version (User Guide 2009). You'll see your Sample Volume signal strength is extremely low and you will need to add some scatterers to the water column to improve this.

 

P.J.