Abstract: Methods and systems for determining a geophysical position of an object in an underwater channel are provided. Acoustic signals from at least two sources are received by a receiver of the object. The acoustic signals have a frequency corresponding to at least one waveguide mode associated with the underwater channel, where the acoustic signals are transmitted at predetermined transmission times. An arrival time for the at least one waveguide mode is determined from the received signals, based on the predetermined transmission times. The geophysical position is determined based on the arrival time and a modal group velocity for the at least one waveguide mode.

Abstract: The present disclosure provides for an inflatable foam pillow having a support layer. More particularly, the present disclosure provides for an inflatable foam pillow comprising a support layer, a shell, and a housing layer attached to the shell which surrounds the support layer and secures the support layer against a side wall of the shell. In some embodiments, the shell may be an inflatable bladder. In some embodiments, the pillow may further include a valve or pump for inflating, holding or releasing the air from the pillow.

Abstract: Methods and systems for determining a geophysical position of an object in an underwater channel are provided. Acoustic signals from at least two sources are received by a receiver of the object. The acoustic signals have a frequency corresponding to at least one waveguide mode associated with the underwater channel, where the acoustic signals are transmitted at predetermined transmission times. An arrival time for the at least one waveguide mode is determined from the received signals, based on the predetermined transmission times. The geophysical position is determined based on the arrival time and a modal group velocity for the at least one waveguide mode.