jremington:
I take it you are no longer interested in measuring the amplitude of the return pulse, just receiving multiple echos.That can be done with a few, but not all, of the available ultrasonic modules. One example includes the old-fashioned Polaroid modules once used in cameras, which are still available and work astonishingly well: http://www.uoxray.uoregon.edu/polamod/
The modern versions of this module are sold by SensComp: http://www.senscomp.com/
Thanks for the links, I'll check them.
I still am interested in measuring the amplitude, however I think it is better to go with baby steps on this. Would there be a method to measure the amplitude? We would need to be able to set the output in decibels and measure in decibels the returning echo. Any sensor able to do it?