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: An imaging lidar apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light is presented. The imaging lidar apparatus is mounted on an airborne platform and including light pulse generating means, reflected light pulse detection means and computer control means. A discrete vehicle is towed by a cable connected to the airborne platform. The discrete vehicle houses optics for receiving or transmitting light pulses. Fiber optic communication may be used to transmit the light pulses along the cable between the airborne platform and the towed vehicle.

Abstract: An airborne imaging lidar (light detection and ranging) sensor is provided which employs multiple pulsed laser transmitters, multiple gated and intensified array camera receivers, an optical scanner for increased field of regard, and a computer for system control, automatic target detection and display generation. The laser transmitters and multiple camera receivers are optically boresighted to the optical scanner (e.g., oscillating flat mirror) for an increased swath width perpendicular to the aircraft heading. The several laser transmitters are coupled for increased power and system sensitivity.

Abstract: A device is provided for expanding, reshaping, modifying the intensity distribution and projecting a beam of radiation such as light. The present invention comprises a four sided, internally mirrored tube of polygonal (i.e., rectangular) cross-section wherein the cross-sectional area of the tube expands (generally linearly) with respect to tube length from a first end to a second end. The first end of the tube is associated with a plano-concave (or equivalent) lens and the second end of the tube is associated with a generally flat pane exit optic which includes optical edging for refracting perimeter rays back into the desired field of view. A practical application for the present invention is laser photogrammetry wherein typically it is desired (1) to expand a laser beam of circular cross-section, (2) to reshape the beam into a desired cross-section, usually rectangular, and (3) to project the reshaped beam upon a distant surface.

Abstract: An electro-optical camera system is presented. In accordance with the present invention, a light source (e.g. laser) is modulated by an electro-optic modulator (such as a Pockels cell) and transmitted out through an optical system toward a static target scene. The light backscattered from the target scene is then focused by the same optics back through the same Pockels cell onto a two-dimensional array camera such as a CCD or a CID (charge-couple device or charge injection device). A computer determines the frequency modulation period of each pixel in the array as the frequency of the electro-optic modulator is varied. This period is inversely proportional to the range of the target in the direction defined by the pixel location. Thus, all three spatial coordinates (two angles and a range) of each target area sensed by each pixel are determined. The computer will display the array of range data using a suitable output device such as a video display unit or a printer.

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 system for determining the magnitude of loads on rotating helicopter components from sensor signals remotely measured on the helicopter fuselage is characterized by a controller which samples the sensor signals according to phase. These measured signals are presented to a coefficient programming module where they are combined with correlation signals to correlate the measured signal components with the desired parameter, such as flatwise bending moments of a helicopter blade. The correlation signals are established in a calibration process that determines the independent values of the measured signals using a Jones orthoganization process. The signals output from the module are recombined to provide a time dependent signal corresponding to the desired parameter. The present system avoids decomposition and recomposition of the measured signals and therefor operates in real time.

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: A wavefront aberration sensor includes a beam splitter, one or more aberration sensor modules and a photodetector for sensing total light power. The aberration sensor modules each provide two voltage outputs from a pair of photodetectors. Differences in the voltage pairs are normalized by the total light power to represent signed aberration amplitudes of phase aberrations present in an input optical beam. The aberration amplitudes may be combined in a digital computer to provide a reconstructed wavefront.

Abstract: A segmented mirror control system comprises an array of structural elements (e.g. mirrors) which can be actively positioned to maintain an accurate pre-determined overall shape. The present invention is "active" and so may be characterized as an Active Segmented Mirror Control "ASMC". The segments of a mirror or the reflecting panels, in for example, a radiotelescope, may be continually adjusted with ASMC to provide an accurate reflecting mirror of very large diameter even when disturbed by external forces. ASMC is a closed loop control system. That is, an array of sensors is first used to measure differential position errors. This data is then processed to determine position actuator commands. Finally, these commands are used to move the segments until the sensors are nulled and the desired shape is obtained.

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.

Abstract: A system is presented for the remote detection and imaging of objects at night. In accordance with the present invention, a laser is used to generate short pulses of infrared light with pulse widths on the order of nanoseconds. The laser light is expanded by optics and projected at the target scene. An intensified CCD (charge coupled device) camera is electronically shuttered after an appropriate time delay such that the image formed by the camera is composed of infrared light backscattered by the target from a range of r.

Abstract: An improved imaging light detection and ranging (lidar) system is presented which provides variable time delay range gating across a selected image. Variable time delay range gating across an image is accomplished using a plurality of imaging cameras which are individually triggered after preselected delays to obtain multiple subimages. These multiple subimages are then put together in a mosaic in a computer to provide a complete image of a target plane using only one light pulse.

Abstract: 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.