Amplitude Range Normalization

Hi,

I have been looking into using the signal amplitudes (acquired with an HR profiler) as a proxy for SSC.  In Nortek TN-3 I found the following equation for range-normalized echo level:

EL = Amp*.43 + 20log(R) + 2alpha_w*R + 20R integral(alpha_p)*dr

I used only the first two terms, i.e. EL = Amp*.43 + 20log(R), and find that the EL values are too low in the first few range bins.  Is there a way to correct this?  The range bins are from 0.2 to 1m at 5-cm intervals.  The profiler was up-looking with tidal depths that ranged from 0 - 2m.

Thanks for any help.

John

Dalhousie University

Halifax, Nova Scotia

Dear John

The equation in TN-3 is valid for the acoustic far field and it is cannot really be used close to the transducer. To get a good expression, you have to integrate the nearfield equation (can at least be done numerically).  Another way to do this is to establish a base profile when the water is fairly clear and assume this represents of a low but vertically constant scattering level.  You can then subtract this base profile from all the other profiler and think of it as an "anomaly profile".  Just be sure to compensate for large variations in temperature (which can change the base profile) and changes in the supply voltage over time.

Best regards, Atle Lohrmann