KEYWORDS: Sensors, Cameras, Receivers, Imaging systems, LIDAR, Stereoscopic cameras, Land mines, Signal to noise ratio, 3D image processing, Image processing
Under the Office of Naval Research's Organic Mine Countermeasures Future Naval Capabilities (OMCM FNC) program, Lite Cycles, Inc. is developing an innovative and highly compact airborne active sensor system for mine and obstacle detection in very shallow water (VSW), through the surf-zone (SZ) and onto the beach. The system uses an
innovative LCI proprietary integrated scanner, detector, and telescope (ISDT) receiver architecture. The ISD tightly couples all receiver components and LIDAR electronics to achieve the system compaction required for tactical UAVintegration while providing a large aperture. It also includes an advanced compact multifunction laser transmitter; an industry-first high-resolution, compact 3-D camera, a scanning function for wide area search, and temporally
displaced multiple looks on the fly over the ocean surface for clutter reduction. Additionally, the laser will provide time-multiplexed multi-color output to perform day/night multispectral imaging for beach surveillance. New processing algorithms for mine detection in the very challenging surf-zone clutter environment are under development, which offer the potential for significant processing gains in comparison to the legacy approaches. This paper reviews the legacy system approaches, describes the mission challenges, and provides an overview of the ROAR system architecture.
KEYWORDS: LIDAR, Sensors, Signal to noise ratio, Polarization, Signal detection, Target detection, 3D acquisition, Transmitters, Detection and tracking algorithms, Error analysis
High-resolution three-dimensional flash ladar system technologies are under development that enables remote identification of vehicles and armament hidden by heavy tree canopies. We have developed a sensor architecture and design that employs a 3D flash ladar receiver to address this mission. The receiver captures 128×128×>30 three-dimensional images for each laser pulse fired. The voxel size of the image is 3”×3”×4” at the target location. A novel signal-processing algorithm has been developed that achieves sub-voxel (sub-inch) range precision estimates of target locations within each pixel. Polarization discrimination is implemented to augment the target-to-foliage contrast. When employed, this method improves the range resolution of the system beyond the classical limit (based on pulsewidth and detection bandwidth). Experiments were performed with a 6 ns long transmitter pulsewidth that demonstrate 1-inch range resolution of a tank-like target that is occluded by foliage and a range precision of 0.3” for unoccluded targets.
KEYWORDS: LIDAR, Signal to noise ratio, Imaging systems, Receivers, Scattering, Light scattering, Data modeling, Pulsed laser operation, Sensors, Wind energy
Our previous comparisons of the SNR and resolving power of various lidar approaches used modulation transfer functions to estimate the effects of surface waves. That technique yields statistical performance estimates, but gives little insight into the appearance of individual images. This paper presents a complementary method, simulating images for the various systems. The images are generated with a numerical code combining ray tracing and small-angle scattering theory with a state-of-the-art, dynamic, surface-wave generator. The resulting images realistically simulate the refractive effects of the ocean waves, providing visual confirmations of our previous analytical results. They demonstrate the excellent contrast of a STIL for high-resolution image classification. However, the superior energy utilization of the LRG approach, makes it a better method for airborne lidar imaging, with an advantage that grows exponentially with depth. Likewise, a compact rectangular array of time- resolved pixels perform search tasks better than does a STIL. These simulations will also allow us to develop optimal strategies for image-by-image processing of LIDAR data.
This paper presents recent experimental and theoretical results regarding the dynamic range and noise performance of ICCD cameras which use micro-channel plate (MCP) image intensifiers. Vendor specifications for image intensifiers using these devices suggest that the noise factor is in the range of 1.6 to 2.2 for Gen II intensifiers and 3.5-4.2 for Gen III intensifiers which use filmed MCPs to extend the GaAs photo cathode lifetime. Our experimental results suggest that the ICCD noise factor increases dramatically as the gain is reduced to accommodate higher background light levels. Noise factors in excess of 60 have been observed. For most applications where the MCP is operated at high gain, this behavior is never encountered. However, for applications which use the MCP as a low-gain device, such as active laser range-gated systems operated in high background reflectance conditions, the imaging performance can be severely degraded. A model for the gain dependent ICCD noise factor has been developed which will be compared with the experimentally observed effects. Keywords: Micro-channel Plate, MCP, Noise Factor, Intensified CCD, ICCD, Dynamic Range, Range-Gating, Laser LineScan.
Imaging lidar, in which light detection and ranging is implemented with sufficient spatial resolution to resolve the size and shape of an object, has demonstrated impressive performance for detecting and classifying underwater targets. During 1996 the U.S. Navy deployed its first imaging lidar system with Naval Air Reserve Squadron HSL-94. This paper reviews the Magic LanternR system and discusses new technology and trends for future systems.
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