Correlations greater than 100?

Hi again,

When we deployed our HR Aquadopps in burst mode (in single or 3 beam mode) we find the second depth bin has correlations of greater than 100%.  They  increase linearly throughout the burst and reach 4096.  It happens on all three beams and for both of our instruments.  I've attached a picture.  Is there an explanation for this (other than our data being 40 times better than perfect?

Cheers,

Julia

Hi Julia,

The hdr-file that is generated when you convert the data to ASCII shows you the format of the various files that are generated in the conversion process. There you can see that the first two values on each line in the correlation file is the burst and ensemble counters. Since the sen-file contains both the exact time stamp of the data and the burst and ensemble counters as well you can the easily use the burst and ensemble counter in the velocity, amplitude and correlation files to align your data to the exact clock.

So try to do imagesc(c1(:,3:end)') and you will see quite a different plot. Feel free to share that plot with us as well

Cheers,

Sven

Hi Sven,

Thanks for that.  So yes, I'm an idiot -- I just wasn't paying enough attention (I'm too used to the low res aquadopps and thought I knew what was going on, clearly a mistake)!  I had previously cheated with the above plots and just set the caxis to [0 100] so I knew the rest of the data was fine with good correlations almost everywhere (although we do get the occasional burst with a line/depth of low correlations, oddly enough not always associated with disturbances in backscatter.)

Cheers,

Julia

Hi Julia,

No worries, nice to get an easy question once in a while. Regarding the line/depth with low correlations the explanation is probably that in the backscatter plot you only see the signal strength that is the result from the first ping. If we had stored the amplitude from the second ping instead you would probably have seen that the first ping hits something at some distance that causes interference when the data for the second ping is measured. To get rid of this you may want to check your setup against the recommended lag in the up/down looking configurations in the standard tab of the configuration setup.

Cheers,

Sven