A submerged object indication system is carried from an aircraft flying above the water. A laser pulse generator directs a pulse at a small water area which may be 25 feet in diameter, and the receiver receives the air-water interface reflection which gates open a channel for receiving a submerged object reflection. A time delay is connected between an optical shutter and the detection circuit which receives the air-to-water interface reflection with the time delay related to the depth at which an object reflection is observed. The air-to-water interface signal can also be used to drive an altimeter with signals displayed visually on a cathode-ray tube display. The light source is in the blue-green portion of the spectrum, with the light pulse lengths being about 0.01 microseconds.
This application is filed as a division of application Ser. No. 345,674, filed on Feb. 18, 1964, and granted on May 27, 1969 as U.S. Pat. No. 3,446,555 entitled "Optical Ranging and Detection System for Submerged Objects."
An optical means for detecting and/or communicating with underwater objects rom airborne platforms wherein a number of laser sources are collimated so as to illuminate a particular portion of the ocean surface from the airborne platform. Thereafter, use is made of the non-linear optical phenomena resulting from the interaction of the various source characteristics (power and wavelength) with the water media to detect modulation of the specularly reflected energy to provide indications of the presence of submerged objects.
A system of ocean depth sounding from the air which consists in projecting an infrared beam (2) down normal to the ocean surface along a forward travel path to backscatter a signal to a receiver (10) to measure distance to the ocean surface, and simultaneously projecting down a green beam (1) to sweep across the direction of travel to backscatter a series of signals from the ocean bottom over an extended width to a second receiver (11), adjusting the receiver gain from the green signal to achieve optimum ocean bottom measurement and calculating ocean depth from the infrared and green signal differential.
A system is provided including a pulsed source of radiation and a gated sensor for responding to optical returns from a predetermined range. A high pulse repetition rate and short duty cycle are employed in order to obtain real time response from the receiver. The receiver is gated with a wave form having a sharp rise time to provide the capability of backlighting selected targets and improving resolution.
4277167 - Depth mapping system - Owned by The United States of America as represented by the Secretary of the Navy (Washington, DC)
A depth mapping system is carried from an aircraft flying above the water. pulsed laser directs a pulse at a predetermined water area and a multi-apertured photomultiplier tube receives backscattered or reflected radiation signals from both the air-water interface and a submerged surface. A signal comparator simultaneously compares each of the reflected radiation signals against the air-water interface radiation signal and drives a CRT display which illustrates the depth of the reflecting surface over the predetermined area.
A novel timing control method is utilized in conjunction with an imaging lidar system of the type disclosed in U.S. Pat. No. 4,862,257. This novel timing control is employed in applications wherein the lidar system is mounted on an airborne platform. The timing control method of this invention completely eliminates the glint detector with associated signal conditioner used in the system of U.S. Pat. No. 4,862,257, and instead, relies upon a signal derived from the aircraft altimeter to continually provide platform altitude status. Since the entire system is under the control of a computer, the altimeter signal can be interpreted and used to adjust total delay so as to automatically track changing platform altitude. It is now possible to initiate all timing from the occurrence of the laser "lamp fire" signal. The total delay to camera "gate on" is now the "lamp-to-laser" delay, plus round trip platform altitude delay (computer from the altimeter signal), plus desired water depth delay, less system delays.
