John T. Sackos

Scannerless range imaging with a square wave

Scannerless range imaging (SRI) is a unique approach to three dimensional imaging without scanners. SRI does, however, allow a more powerful light source to be used as compared to conventional laser radar (LADAR) systems due to the speed of operation associated with this staring system. As a result, a more efficient method of operation was investigated. As originally conceived, SRI transmits a continuous intensity modulated sinusoidal signal; however, a square wave driver is more energy efficient than a sinusoidal driver. In order to take advantage of this efficiency, a square wave operational methodology was investigated. As a result, four image frames are required for the extraction of range using a square wave to unambiguously resolve all time delays within one time period compared to a minimum of three frames for the sinusoidal wave.

The emerging versatility of a scannerless range imager

Sandia National Laboratories is nearing the completion of the initial development of a unique type of range imaging sensor. This innovative imaging optical radar is based on an active flood-light scene illuminator and an image intensified CCD camera receiver. It is an all solid-state device (no moving parts) and offers significant size, performance, reliability, simplicity, and affordability advantages over other types of 3D sensor technologies, including: scanned laser radar, stereo vision, and structured lighting. The sensor is based on low cost, commercially available hardware, and is very well suited for affordable application to a wide variety of military and commercial uses, including: munition guidance, target recognition, robotic vision, automated inspection, driver enhanced vision, collision avoidance, site security and monitoring, terrain mapping, and facility surveying. This paper reviews the sensor technology and its development for the advanced conventional munition guidance application, and discusses a few of the many other emerging applications for this new innovative sensor technology.

Characterization of scannerless ladar

Scannerless laser radar (LADAR) is the next revolutionary step in laser radar technology. It has the potential to dramatically increase the image frame rate over raster-scanned systems while eliminating mechanical moving parts. The system presented here uses a negative lens to diverge the light from a pulsed laser to floodlight illuminate a target. Return light is collected by a commercial camera lens, an image intensifier tube applies a modulated gain, and a relay lens focuses the resulting image onto a commercial CCD camera. To produce range data, a minimum of three snapshots is required while modulating the gain of the image intensifier tubes microchannel plate (MCP) at a MHz rate. Since November 1997 the scannerless LADAR designed by Sandia National Laboratories has undergone extensive testing. It has been taken on numerous field tests and has imaged calibrated panels up to a distance of 1 km on an outdoor range. Images have been taken at ranges over a kilometer and can be taken at much longer ranges with modified range gate settings. Sample imagery and potential applications are presented here. The accuracy of range imagery produced by this scannerless LADAR has been evaluated and the range resolution was found to be approximately 15 cm. Its sensitivity was also quantified and found to be many factors better than raster- scanned direct detection LADAR systems. Additionally, the effect of the number of snapshots and the phase spacing between them on the quality of the range data has been evaluated. Overall, the impressive results produced by scannerless LADAR are ideal for autonomous munitions guidance and various other applications.

Characterization of a scannerless ladar system

Performance projections based on the analytical model of a scannerless laser radar system (presented in a companion paper) are compared to laboratory simulations and to field data measurements. Data and characteristics of the system, including camera response, image spatial resolution, and contributions to the signal-to-noise ratio are presented. A discussion of range resolution for this system also is presented, and finally, the performance characteristics of the prototype benchtop system are summarized.

Scannerless terrain mapper

NASA-Ames Research Center, in collaboration with Sandia National Laboratories, is developing a scannerless terrain mapper (STM) for autonomous vehicle guidance through the use of virtual reality. The STM sensor is based on an innovative imaging optical radar technology that is being developed by Sandia National Laboratories. The sensor uses active flood- light scene illumination and an image intensified CCD camera receiver to rapidly produce and record very high quality range imagery of observed scenes. The STM is an all solid- state device (containing no moving parts) and offers significant size, performance, reliability, simplicity, and affordability advantages over other types of 3-D sensor technologies, such as scanned laser radar, stereo vision, and structured lighting. The sensor is based on low cost, commercially available hardware, and is very well suited for affordable application to a wide variety of military and commercial uses, including: munition guidance, target recognition, robotic vision, automated inspection, driver enhanced vision, collision avoidance, site security and monitoring, and facility surveying. This paper reviews the sensor technology, discusses NASAs terrain mapping applications, and presents results from the initial testing of the sensor at NASAs planetary landscape simulator.

Damage of MEMS thermal actuators heated by laser irradiation.

Optical actuation of microelectromechanical systems (MEMS) is advantageous for applications for which electrical isolation is desired. Thirty-two polycrystalline silicon opto-thermal actuators, optically-powered MEMS thermal actuators, were designed, fabricated, and tested. The design of the opto-thermal actuators consists of a target for laser illumination suspended between angled legs that expand when heated, providing the displacement and force output. While the amount of displacement observed for the opto-thermal actuators was fairly uniform for the actuators, the amount of damage resulting from the laser heating ranged from essentially no damage to significant amounts of damage on the target. The likelihood of damage depended on the target design with two of the four target designs being more susceptible to damage. Failure analysis of damaged targets revealed the extent and depth of the damage.

A low-cost, high-resolution, video-rate imaging optical radar

Sandia National Laboratories has developed a unique type of portable low-cost range imaging optical radar (laser radar or LADAR). This innovative sensor is comprised of an active floodlight scene illuminator and an image intensified CCD camera receiver. It is a solid-state device (no moving parts) that offers significant size, performance, reliability, and simplicity advantages over other types of 3D imaging sensors. This unique flash LADAR is based on low- cost, commercially available hardware, and is well suited for many government and commercial uses. This paper presents an update of Sandias development of the Scannerless Range Imager technology and applications, and discusses the progress that has been made in evolving the sensor into a compact, low cost, high-resolution, video rate Laser Dynamic Range Imager.

Range imaging for underwater vision enhancement

This paper present results from a series of preliminary tests to evaluate a scannerless range-imaging device as a potential sensor enhancement tool for divers and as a potential identification sensor for deployment on small unmanned underwater vehicles. The device, developed by Sandia National Laboratories, forms an image on the basis of point-to-point range to the target rather than an intensity image. The range image is constructed through a classical continuous wave phase detection technique which synchronously couples a modulated light source to a gain- modulated image intensifier in the receiver. Range information is calculated on the basis of the phase difference between the transmitted and reflected signal. The initial feasibility test at the Coastal Systems Station showed the device to be effective at imagin glow-contrast underwater targets such as concertina wire. It also demonstrated success at imagin a 21-inch sphere at a depth of 10 feet in the water column through a wavy air-water interface.

Building accurate geometric models from abundant range imaging information

We define two simple metrics for accuracy of models built from range imaging information. We apply the metric to a model built from a recent range image taken at the laser radar Development and Evaluation Facility, Eglin AFB, using a scannerless range imager (SRI) from Sandia National Laboratories. We also present graphical displays of the residual information produced as a byproduct of this measurement, and discuss mechanisms that these data suggest for further improvement in the performance of this already impressive SRI.

Counter-sniper 3D laser radar

Visidyne, Inc., teaming with Sandia National Laboratories, has developed the preliminary design for an innovative scannerless 3-D laser radar capable of acquiring, tracking, and determining the coordinates of small caliber projectiles in flight with sufficient precision, so their origin can be established by back projecting their tracks to their source. The design takes advantage of the relatively large effective cross-section of a bullet at optical wavelengths. Kay to its implementation is the use of efficient, high- power laser diode arrays for illuminators and an imaging laser receiver using a unique CCD imager design, that acquires the information to establish x, y (angle-angle) and range coordinates for each bullet at very high frame rates. The detection process achieves a high degree of discrimination by using the optical signature of the bullet, solar background mitigation, and track detection. Field measurements and computer simulations have been used to provide the basis for a preliminary design of a robust bullet tracker, the Counter Sniper 3-D Laser Radar. Experimental data showing 3-D test imagery acquired by a lidar with architecture similar to that of the proposed Counter Sniper 3-D Lidar are presented. A proposed Phase II development would yield an innovative, compact, and highly efficient bullet-tracking laser radar. Such a device would meet the needs of not only the military, but also federal, state, and local law enforcement organizations.