James Samuel Taylor

Advantages of three-dimensional electro-optic imaging sensors

Electro-optic identification sensors provide photographic quality images and were developed to identify objects of interest on the ocean bottom. Two of these high-resolution sensors are currently in use: one based on Streak Tube Imaging Lidar (STIL) technology and the other based on Laser Line Scan (LLS) technology. Both of these sensors produce high fidelity imagery that is unparalleled in quality for underwater imaging systems. They differ in that LLS sensors produce two-dimensional (2-D) contrast images only while STIL produces three-dimensional (3-D) data that can be rendered into 2-D contrast and range maps (images). Although still an emerging technology, recent advances have begun to point to significant advantages with the supplementary range information (3-D information) in identifying objects of interest on the sea floor. This paper discusses some of these advantages of range information for 3-D visual display, computer aided identification and target recognition, modeling, and the general identification process.

Tracking with two frequency-modulated reticles

A typical reticle tracker includes a single frequency-modulated (FM) reticle to encode target location. This system is not useful for tracking multiple or large targets. A system, using two FM frequency-versus-radius reticles, is presented that allows tracking of these type targets. Results of computer simulations for both the single- and double-reticle tracking systems are presented and their performance is compared and contrasted.

Comparison of continuous and discrete frequency-versus-radius frequency-modulated reticles

We present a general expression for the transmission function of the discrete frequency-versus-radius reticle and compare such a reticle with the more common continuous reticle. A discrete form of the frequency-versus-radius reticle has an integer number of chopping cycles on a single radius. The discreteform limits the resolution of the reticle in the radial direction, but this limit is not severe for small-target images. However, since no phase reversal occurs, electronic processing is simplified.

Underwater partial polarization signatures from the shallow water real-time imaging polarimeter (SHRIMP)

Research has shown that naturally occurring light outdoors and underwater is partially linearly polarized. The polarized components can be combined to form an image that describes the polarization of the light in the scene. This image is known as the degree of linear polarization (DOLP) image or partial polarization image. These naturally occurring polarization signatures can provide a diver or an unmanned underwater vehicle (UUV) with more information to detect, classify, and identify threats such as obstacles and/or mines in the shallow water environment. The SHallow water Real-time IMaging Polarimeter (SHRIMP), recently developed under sponsorship of Dr. Tom Swean at the Office of Naval Research (Code 321OE), can measure underwater partial polarization imagery. This sensor is a passive, three-channel device that simultaneously measures the three components of the Stokes vector needed to determine the partial linear polarization of the scene. The testing of this sensor has been completed and the data has been analyzed. This paper presents performance results from the field-testing and quantifies the gain provided by the partial polarization signature of targets in the Very Shallow Water (VSW) and Surf Zone (SZ) regions.

Laboratory characterization and field testing of the tunable filter multispectral camera

The Coastal Systems Station, in concert with Xybion Corp. has developed a tunable-filter multispectral imaging sensor for use in airborne reconnaissance. The sensor was completed in late 1999, and laboratory characterization and field- testing has been conducted since. The Tunable Filter Multispectral Camera (TFMC) is an intensified, gated, and tunable multispectral imaging camera that provides three simultaneous channels of 10-bit digital and 8-bit analog video from the near-UV to the near-IR. Exposure and gain can be automatically or manually controlled for each channel, and response has been linearized for approximate radiometric use. Additionally, each of the three channels as a separate programmable liquid-crystal tunable filter with a selectable center wavelength settings to which can be applied 100 different retardances for each of three channels. This paper will present setups, analysis methods, and preliminary results for both the laboratory characterization and field- testing of the TFMC. Laboratory objectives include measures of sensitivity, noise, and linearity. Field testing objectives include obtaining the camera response as the lighting conditions approached sunset of a clear day, signal-to-clutter ratios for a multiplicity of channel wavelength combinations and polarizations against several backgrounds, and resolution performance in field-conditions.

Tracking with two FM reticles

A tracking system is presented which uses two FM frequency-versus-radius reticle allowing the tracking of multiple targets or large targets. The results of computer simulations of both single and double reticle tracking systems are presented. The performances of the two systems are compared.

Environmental factors impacting the performance of airborne lidar sensors in the surf zone

The surf zone is a challenging environment for conducting mine countermeasures operations. The performance of acoustic sensors in this environment is extremely limited. Airborne LIDAR sensors have significantly better prospects for successfully working in this environment. However, the complex environment will be a driving factor limiting their performance. The environmental factors influencing the performance of airborne LIDAR sensors will be examined in this paper. These factors can be highly dynamic. Breaking surf action causes bottom sediment resuspension and the formation of bubbles and foam. The resuspended sediments then begin the process of settling, while the bubbles and foam begin to dissipate. All of these phenomena impact the optical properties of the water, which, in turn, impact the performance of the LIDAR system. An experiment was designed and conducted to study the impact of these dynamic processes on the optical properties of the water. The experiment was conducted in September 2002 at the Army Corp of Engineers Field Research Facility in Duck, North Carolina. Preliminary results from the analysis of this data are presented here. This work is being conducted by the Airborne Littoral Reconnaissance Technology (ALRT) project under ONR sponsorship.

Process for the development of image quality metrics for underwater electro-optic sensors

Electro-optic identification (EOID) sensors have been demonstrated as an important tool in the identification of bottom sea mines and are transitioning to the fleet. These sensors produce two and three-dimensional images that will be used by operators and algorithms to make the all-important decision regarding use of neutralization systems against sonar contacts classified as mine-like. The quality of EOID images produced can vary dramatically depending on system design, operating parameters, and ocean environment, necessitating the need for a common scale of image quality or interpretability as a basic measure of the information content of the output images and the expected performance that they provide. Two candidate approaches have been identified for the development of an image quality metric. The first approach is the development of a modified National Imagery Interpretability Rating Scale (NIIRS) based on the EOID tasks. Coupled with this new scale would be a modified form of the General Image Quality Equation (GIQE) to provide a bridge from the system parameters to the NIIRS scale. The other approach is based on the Target Acquisition Model (TAM) that has foundations in Johnson’s criteria and a set of tasks. The following paper presents these two approaches along with an explanation of the application to the EOID problem.

Frequency-modulated reticle trackers in the pupil plane

An appealing approach to implementing spinning reticle trackers in the pupil plane is presented. The advent of research in spatial light modulators and addressable mirror arrays may allow achievement of pupil plane processing in the next few years. Reticles were generated with the general FM reticle equation, and FFTs of the reticles were obtained. Magnitude and phase plots of these reticles are shown. The magnitude plots are easily understood; however, the phase plots will take more study before implementation is tractable.