How to detect impulse like peaks - Matlab
Try this:


Convert all values to dB (looks like you've already done this.)
Run the resulting data through a high pass filter with a cut off of 1/4 of your sampling rate.
Select a threshold (looks like 10dB would be good.)  Anything above the threshold is peak.


You'll probably want to use a FIR filter for the highpass - the signal will be delayed depending on the length of your filter, but you can account for that easily since it will be an integer number of samples.

I've been thinking of making an acoustic echogram, and this is the method I thought up to get rid of clutter and show just the sharp reflections.