Abstract: A navigational system for surface vessels that provides warning of impending grounding occurrences. A data base of bottom contours and submerged obstructions is compared to various indicators of the surface vessel's position and motion to provide alerts and to display bottom hazards ahead of the vessel.

Abstract: A schlieren imaging system provides quantitative images suitable for testing medical equipment. One embodiment includes precision optics which form an image of a volume of a medium through which an ultrasonic acoustic wave propagates. A spatial filter passes diffracted light but blocks other light. A camera forms an image of the medium from the diffracted light so that regions of the medium which diffract light have higher light intensity in the image. From image intensities, a processor determines acoustic pressures or intensities, typically as a value indicating an integral of the acoustic pressure or intensity along an optical path through the volume. Integrated pressure is determined from a look-up table which relates predicted light intensity to pressure values which cause the predicted light intensity. The system is calibrated by forming an image of a reference ultrasonic acoustic wave and determining a relation between the image intensities and predicted intensities.