The Anti-Invasion Mine Signature Measurement and Assessment for Remote Targeting (AIMSMART) program has undertaken a lidar mine signature data collection for ONR to characterize electro-optic (EO) signatures of anti-invasion mines and environmental factors affecting their detection in the littorals. Two lidar sensors, one 3-D and one polarimetric, both developed by Arete, were fielded at the FRF test facility in Duck, NC. Data were collected with these sensors over a wide variety of mine targets, obstacles, backgrounds, water quality, and wave movements. The principle goal of this analysis is to characterize lidar signature features, especially 3-D, of in-water mines and correlate those features to physical processes in the VSW and SZ environments. This paper describes the approach to characterizing these mine signatures and presents initial results from the analysis.
Flash lidars can produce high-resolution data in all three spatial dimensions. In addition, even low repetition rate lasers result in extensive data sets. The challenge presented by these systems is: “How do we reduce the inherently large sets of data to information that is useful to the human operator.” We discuss both sensor specific and general signal-processing tools developed to render 3D lidar data in a fashion that allows man in the loop identification of targets. Data collected during an airborne field test at Redstone Aresenal Test Area Three in Huntsville using Arete Associates FLASH lidar is used to present specific examples.
Two separate data collections using Arete Associates' FLASH lidar are presented. The hardware and the experimental arrangements are discussed. An airborne data collection over military targets in clear and obscuring camouflage environments provided high-resolution three-dimensional images for combat identification purposes. In the second field test, the sensor was suspended from a crane above the ocean surface to acquire FLASH imagery of anti-landing mines and obstacles in the highly turbid surf zone environment over a wide range of surf zone conditions.
A 64x64-pixel Flash (scannerless) lidar system that uses a streak tube to achieve range-resolved images is demonstrated. An array of glass fibers maps light from an area in the focal plane of an imaging lens to multiple rows of fibers on the streak tube's photocathode. The time-resolved backscatter return for all 4096 image pixels is recorded during one integration-time of a CCD camera that is coupled to the streak tube's phosphor screen. Data processing yields 64x64-pixel contrast (intensity) and range images for each laser pulse. Range precision better than 2.5% of the range extent is exhibited for a wide variety of targets and terrains at image rates up to 100Hz. Field test imagery demonstrated the capability of the Flash lidar system for imaging vehicles hidden by a tree canopy as well as for imaging sub-surface mine-like targets in the ocean.
A multi-dimensional laser radar sensor is developed to perform 3D imaging polarimetry. The imaging polarimeter is an extension of the existing, well-developed Streak Tube Imaging Lidar technology. With polarization optics added to the transceiver system, simultaneous capture of 3D high- resolution polarimetric and reflectance imagery is achieved over wide fields of view. Laboratory and field experiments exhibit the capability of the imaging polarimeter for enhancing clutter reduction, image segmentation, and target discrimination for low contrast and camouflaged targets.
An imaging lidar system is developed for capturing laser- induced fluorescence imagery. With minor changes to the transmitter and receiver optics, the system operates in a number of different modes including 3D multispectral, hyperspectral, multi-excitation hyperspectral, and fluorescence-lifetime hyperspectral. All of these sensor functions provide discriminating capabilities for targets exhibiting spectral fluorescence signatures.
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