Abstract: An imaging lidar system for underwater applications is presented which is well suited for imaging and detecting underwater targets suspended above and on the bottom in shallow and coastal water. The present invention provides the capability for rapid and reliable search, detection, classification and localization of objects in the surf zone which may present hazards to navigation and utilization of coastal areas as well as undesirable effluents and biological fouling of underwater objects. The present invention provides an improved bottom tracker, improved ability to deal with brightness variation and surface glint, and computerized real time detection algorithms.

Abstract: An imaging UV/visible fluorosensing and Raman lidar system comprises an optical sensor for simultaneously measuring temporally, spatially and spectrally resolved laser backscatter from on the land, on or beneath the surface of bodies of water and in the atmosphere and utilizes "active" interrogation or "passive" interrogation for remotely and non-destructively probing the spectrally-dependent optical properties of a scene. In the "active" mode, the optical sensor of this invention comprises a transmitter (preferably a tunable solid state laser) which emits pulses of coherent light through a variable or adjustable field-of-view telescope whereupon the light pulses are then propagated towards a scene (e.g., land, sea or atmosphere). Thereafter, laser backscatter is collected by a second variable field-of-view telescope and directed to an imaging system and spectrally dispersive optical subsystem.

Abstract: An underwater maneuverable vehicle is presented which carries an explosive charge and can be used for immediate removal or destruction of various menaces to navigation and other underwater hazards. The battery powered vehicle is air dropped from a platform which carries an imaging lidar system for detection and is operated and navigationally controlled in conjunction with an imaging lidar system. In accordance with an important feature of this invention, an optical lidar downlink is used to control the submerged underwater maneuverable vehicle from an airborne platform. The downlink is pulse spaced modulated. Command signals are secure, and are decoded aboard the vehicle. Control in speed, heading and depth, as well as command detonation are available using this technique.

Abstract: An imaging UV/visible fluorosensing and Raman lidar system comprises an optical sensor for simultaneously measuring temporally, spatially and spectrally resolved laser backscatter from on the land, on or beneath the surface of bodies of water and in the atmosphere that utilizes "active" interrogation or "passive" interrogation for remotely and non-destructively probing the spectrally-dependent optical properties of a scene. In the "active" mode, the optical sensor comprises a transmitter (preferably a tunable solid state laser) which emits pulses of coherent light through a variable or adjustable field-of-view telescope whereupon the light pulses are then propagated towards a scene (e.g., land, sea or atmosphere). Thereafter, laser backscatter is collected by a second variable field-of-view telescope and directed to an imaging system and spectrally dispersive optical subsystem.

Abstract: An imaging lidar system is presented which is adapted to decrease the backscattering at the receiver when a target is viewed in reflection and to increase the backscattered reflection when the target is viewed in obscuration by operating the airborne lidar imaging system bistatically in the former case, and monostatically in the latter case. In accordance with a first embodiment of the present invention, a retractible prism and remote reflecting mirror are used to direct the laser transmitter beam downward. The reflecting mirror is offset so that there is a finite angle between the transmitter optical path and the path of the light reflected back into the CCD framing camera. The angle can be varied by moving the reflecting mirror along a track or rail with the appropriate adjustment to the mirror so that the transmitter beam is completely captured and directed downward to illuminate the area viewed by the camera.

Abstract: Deployed, air dropped buoys are presented which can be used as calibrated targets for imaging lidar systems. In this way, oceanographic optical measurements can be made to determine in advance how an imaging lidar system will perform at the time of its deployment. This calibrated optical buoy is deployable from an airborne platform. The target is illuminated by an imaging lidar system and the target reflection is compared with the backscattering from the ocean volume illuminated. At the same time, measurements of light intensity are carried out to provide a direct measurement of the attenuation in the ocean. These data are taken at all depths and the results telemetered to the airborne lidar platform. In addition, a simplified embodiment is presented which uses the imaging lidar system to obtain both backscatter and attenuation. This simplified embodiment requires no telemetry.

Abstract: A novel data processing technique is provided for employing a physical model as an element in a process for automatic target detection of a target viewed by an imaging lidar system. The present invention obtains estimates for the mean and variance of the probability distributions for random video levels which are output from a camera. These estimates are obtained under various assumptions about the state of the target.

Abstract: An imaging UV/visible fluorosensing and Raman lidar system comprises an optical sensor for simultaneously measuring temporally, spatially and spectrally resolved laser backscatter from on the land, on or beneath the surface of bodies of water and in the atmosphere. The present invention utilizes "active" interrogation or "passive" interrogation for remotely and non destructively probing the spectrally-dependent optical properties of a scene. In the "active" mode, the optical sensor of this invention comprises a transmitter (preferably a tunable solid state laser) which emits pulses of coherent light through a variable or adjustable field-of-view telescope whereupon the light pulses are then propagated towards a scene (e.g., land, sea or atmosphere). Thereafter, laser backscatter is collected by a second variable field-of-view telescope and directed to an imaging system and spectrally dispersive optical subsystem.

Abstract: An underwater maneuverable vehicle is presented which carries an explosive charge and can be used for immediate removal or destruction of various menaces to navigation and other underwater hazards. The battery powered vehicle is air dropped from a platform which carries an imaging lidar system for detection and is operated and navigationally controlled in conjunction with an imaging lidar system.

Abstract: An underwater maneuverable vehicle is presented which carries an explosive charge and can be used for immediate removal or destruction of various menaces to navigation and other underwater hazards. The battery powered vehicle is air dropped from a platform which carries an imaging lidar system for detection and is operated and navigationally controlled in conjunction with an imaging lidar system. In accordance with an important feature of this invention, an optical lidar downlink is used to control the submerged underwater maneuverable vehicle from an airborne platform. The downlink is pulse spaced modulated. Command signals are secure, and are decoded aboard the vehicle. Control in speed, heading and depth, as well as command detonation are available using this technique.

Abstract: A novel data processing technique is provided for detecting, locating and identifying targets from a plurality of images generated by an imaging sensor such as an imaging lidar system. The present invention employs physical models of signals produced by target objects of interest. Such a model based detection system globally processes frames of data to determine the existence and location of component elements that characterize the target being modeled.

Abstract: An imaging lidar system is presented which utilizes internal or external transmitter beam pattern referencing for improved imaging lidar performance. In general, the present invention samples the laser output at or near the source to obtain a reference of the signal intensity distribution. This reference signal includes any anomalous spatial intensity distributions (associated with the output of the laser transmitter) which can then be discounted or subtracted out from the signals received from the target area of interest.

Abstract: The present invention employs an optical filter which rejects substantially all wavelengths except for a selected wavelength. This invention eliminates most optical noise (e.g., solar noise) in LIDAR (light detection and ranging) imaging systems as well as LIDAR bathymetry systems and underwater submarine communication systems. The selected wavelength corresponds to the transmission wavelength of the laser. In accordance with the LIDAR systems of the present invention, a laser beam of the selected wavelength is projected at a body of water wherein a return beam is generated. The reflected or backscattered return beam is collected by optics which then directs the beam at the filter. The beam is filtered so that substantially all other wavelengths not corresponding to the selected wavelength are rejected, thereby eliminating most optical noise, particularly solar noise. The filtered beam is then detected.

Abstract: The present invention uses tunable and fixed frequency lasers as an optical light source in underwater communications systems. This invention provides a high energy, short pulse length laser output which is tunable to or set at a desired wavelength. The tuning is used for performance optimization of the communications systems. An example of performance optimization is the tuning to or setting of the laser at the so-called Jerlov minimum, which is dependent upon the optical characteristics of the particular water used. The system described herein is used as an optical communications downlink employing one or more atomic resonance filter detectors. This invention has the effect of significantly improving the optical signal to noise ratio.

Abstract: An imaging lidar system is presented which employs a multipulse multiple gating system which is particularly well suited for underwater imaging. The imaging lidar system of this invention utilizes a multipulse Q-switched laser operating within the pumping envelope of discharging flash lamps (or other means) to cumulatively illuminate a single frame on a camera (e.g., CCD camera) while the camera is gated repetitively so that each pulse is "observed" at the same depth; that is, the gated camera views that same illuminated area in the ocean. The sequence is repeated at a frequency which is both the laser pulse repetition rate and the camera frame rate. The present invention also allows the use of multiple cameras with frame addition or with frames processed separately. As a result, energy is extracted from the laser in the form of short (1-10 nsec) pulses by rapidly Q-switching during the time the laser is being pumped by the flashlamps.

Abstract: A method is provided in which the pulse stretching effects of radiation trapping can be minimized in atomic resonance filter detectors or QLORD filter detectors of the type described in U.S. Pat. No. 4,292,526. The QLORD detector of this invention which consists of two spectral bandpass filters, one each located on either side of a transparent cell containing an alkali metal vapor (preferably cesium vapor), and responds to an incoming pulse in the visible part of the spectrum of light (actually 420 to 480 nm), emitting a pulse of infrared light. If the transparent cell contains alkali metal vapor only, the infrared light pulse will be stretched, because of resonant trapping within the alkali metal vapor. However, in accordance with the present invention, an inert buffer gas (namely helium) is added to the alkali metal vapor. This buffer gas allows the rapid leakage of infrared light photons from the wings of the energy spectrum, and hence a more rapid response to the incoming pulse.

Abstract: A spectral bandpass filter with a sharp angle independent absorption edge for reducing optical noise is used in conjunction with a known atomic resonance filter-detector or QLORD detector such as described in U.S. Pat. No. 4,292,526. The QLORD detector comprises two spectral bandpass filters enclosing or sandwiching a chamber containing atomic vapor. In accordance with the present invention, between the high-pass filter and the atomic vapor is placed a strip of volume absorbing filter material. The high pass filter has already admitted light which can be absorbed by the atomic vapor thereby excluding that incoming light which is in the spectral range of the light readmitted by radiative decay. The volume absorbing material then makes the further attenuative selection between the various sets of hyperfine lines.

Abstract: The present invention uses tunable and fixed frequency lasers as an optical light source in imaging laser detection and ranging (LIDAR) systems. This invention provides a high energy, short pulse length laser output which is tunable to or set at a desired wavelength. The tuning is used for performance optimization of lidar system; and for scientific investigations carried out using these systems. An example of performance optimization is the tuning to or setting of the laser at the so-called Jerlov minimum, which is dependent upon the optical characteristics of the particular water used. The improved system may be used for scientific investigation, such as determining K.sub.s (the frequency-dependent optical attenuation coefficient) in the ocean at depth, as well as imaging various opaque objects under battlefield conditions, at depth. This invention has the effect of significantly improving the optical signal to noise ratio for all of these applications.

Abstract: A two wavelength lidar imaging system for underwater applications is presented which employs image subtraction. More specifically, a two wavelength lidar system is presented wherein two substantially simultaneously timed laser pulses of different wavelengths are emitted and are expanded by optics to illuminate the water below. A framing camera is then gated to receive light reflected or scattered back from the water. The light backscattered is filtered through narrow pass filters before it is recorded at the gated cameras. A specific application is disclosed in which the lidar imaging system is used to detect the passage of internal waves or other anomalies appearing in the ocean.

Abstract: Variable time delay range gating across an image is accomplished using a single imaging camera. In a preferred embodiment, the imaging camera of the present invention accomplishes adapted range gating and comprises a lens which focuses light onto a substrate having an array of gating electrodes mounted thereon. Both the electrode array and substrate are transparent to light so that the light focussed by the lens passes through the electrode array and substrate to strike a photocathode. The camera of this invention also includes a multiple output power supply connected between the electrode array and a microchannel plate amplifier, an anode, and an imaging array detector which is connected to the anode through a fiber optic bundle. The imaging camera of the present invention will effect adaptive range gating for overcoming the intensity variations and imaging plane problems associated with known light imaging detection and range (lidar) systems.