Abstract: A non-invasive elastic wave fluid level sensing system for use in sludge laden environments, including transmitting and receiving transducers mounted on an outer face of a wall of a container for a fluid and along a propagation path for an elastic wave transmitted through the wall of the container wherein the elastic wave has a frequency of less than 5 kHz, more preferably less than about 2 kHz, and most preferably less than 1 kHz. A signal processor determines a change in a characteristic of the elastic wave between when a fluid is present in the container in the region of the propagation path and when a fluid is not present in the container in the region of the propagation path. One embodiment utilizes multiple horizontally oriented transmitting and receiving transducer pairs to detect levels of the fluid in the container.

Abstract: A hydrophone arrangement, housed within a dome shaped concrete and steel bunker, to accurately establish a bearing of a target object while diminishing potential displacement of the hydrophone arrangement from an initial installed position. A plurality of hydrophones are centrally positioned within the bunker and equally spaced about a periphery of a steel cylindrical member so that each hydrophone receives acoustic energy in a time delay manner with respect to the other adjacent hydrophones so that a bearing determination may be made from information received by a single stand alone bunker. An acoustic horn may also be provided to focus the acoustic energy towards the hydrophones to improve the signal-to-noise ratios and provide control of the phase of the acoustic energy as the energy is received by the hydrophones.