Patent ID: 8730766

Claim:
An underwater seismic system comprising: a first test mass and a second test mass suspended in an underwater platform; a first rigid housing rigidly coupled to the underwater platform and enclosing a first interior region in which the first test mass resides; a second rigid housing disposed proximate to the first rigid housing and rigidly coupled to the underwater platform and enclosing a second interior region in which the second test mass resides; a first motion sensor housed in the first region and coupling the first test mass to the first rigid housing to provide a first response responsive to the motion of the first test mass; a second motion sensor housed in the second region and coupling the second test mass to the second rigid housing to produce a second response responsive to the motion of the second test mass; wherein the second rigid housing and the second region provide an acoustic impedance that is the same as that of seawater to admit acoustic waves into the second region to be sensed by the second test mass; wherein the first region of the first rigid housing is filled with a material such as air or an open-cell foam that has an acoustic impedance more closely matched to the acoustic impedance of air than to the acoustic impedance of seawater to provide a lower acoustic impedance than that of the second rigid housing and the second region, the lower acoustic impedance shielding the first test mass from acoustic waves; wherein the first and second responses are similar in magnitude for platform motion and different in magnitude for acoustic waves.