IERUS Technologies, under subcontract to Tethers Unlimited, is developing a machine vision inspection system for the validation of metallic components additively manufactured in space. The effort has begun with a survey of vision technologies, including stereo vision, structure from motion, light field imaging, and structured illumination. Using the optical data, 3D point clouds will be registered as the object is viewed from multiple orientations. From the point cloud data, a mix of deterministic and machine learning algorithms will be used to identify geometric primitives that can be compared to those included in the computer aided design model. In addition, the system will estimate the surface roughness. Based upon the tolerances required within the CAD, pass/fail criteria will be established and the system will determine if the part passes, fails, or cannot be determined. At the end of the current phase, IERUS will perform a demonstration using a prototype system on a challenge artifact provided by NASA.
IERUS Technologies investigated the feasibility of developing a high resolution, passive MWIR polarimetric imaging system for both day and night operation at short (1 – 5 meters) and long (1 – 2 km) range operation. The sensor system used a micro-polarizer array (MPA) over the focal plane array (FPA) in order to capture four channels of polarimetric information simultaneously. It also used an optical registration array (ORA) over the MPA in order to spatially register the polarimetric information. The MPA-ORA device is integral to the FPA, forming a drop-in-replacement, saving system size and weight relative to other polarimetric imaging technologies. A system was designed for a prototype that mitigates risk and demonstrates the utility of the ORA. The FPA employed is a MWIR array with a reticulated detector array which reduces electrical pixel-to-pixel crosstalk to zero. Polarization and radiometric performance predictions of the design will be presented.
A simulation study was conducted for the purpose of identifying technology improvements for an acquisition sensor for the detection of small objects in clear, sunlit cloud, fog, and mist conditions. Currently available mid-wave infrared (MWIR) and long-wave infrared (LWIR) technologies were studied. In addition, projected sensor technologies anticipated to be available in the near future, as well as idealized systems limited only by aperture size, integration time and instantaneous field of view (IFOV) were modeled. Both standard and polarimetric imaging sensors were included in the study. The Aero-Optical Prediction Tool (AerOPT) was used to model the performance of various sensors operating under the conditions of interest. Results indicate that LWIR systems may extend detection range in fog and mist environments and that polarimetry may reduce false alarm rate for sunlit cloud backgrounds. Importantly, polarimetric imaging does not appear to negatively impact detections.
KEYWORDS: Fiber optic gyroscopes, Mie scattering, Light scattering, Scattering, Monte Carlo methods, Atmospheric particles, Photon transport, Atmospheric propagation, Air contamination, Visibility through fog
Anyone who has driven through fog understands the detrimental effect scattering can have on your ability to see. When light interacts with a scattering center, in this case a fog droplet, it is scattered into a new direction, ultimately turning the world around you into a dull gray haze. In some fogs, visibility can be less than 100 meters. It would be possible to see through turbid media like fog if you can separate the scattered light from the unscattered, or ballistic, light; however, we must understand the light transport properties of the atmosphere to determine the optimum scheme. Here, we present an end-to-end simulation for polarized light transport through fog. Our approach can be summarized in three steps: compute the Mueller matrix for a single scattering interaction, ensemble average a distribution of sizes and shapes, and solve the light transport using a Monte Carlo simulation. For small spherical particles, such as fog, we use Mie theory to calculate the single scattering Mueller matrix, but this approach can be generalized to non-spherical particles using ray tracing for large particles or a T-matrix approach for smaller particles. Through this simulation, we are able to determine a backscattering Mueller matrix and a forward scattering Mueller matrix response function for the atmosphere as a function of position and detection angle.
IERUS Technologies, Inc. and the University of Alabama in Huntsville have partnered to perform characterization and development of algorithms and hardware for adaptive optics. To date the algorithm work has focused on implementation of the stochastic parallel gradient descent (SPGD) algorithm. SPGD is a metric-based approach in which a scalar metric is optimized by taking random perturbative steps for many actuators simultaneously. This approach scales to systems with a large number of actuators while maintaining bandwidth, while conventional methods are negatively impacted by the very large matrix multiplications that are required. The metric approach enables the use of higher speed sensors with fewer (or even a single) sensing element(s), enabling a higher control bandwidth. Furthermore, the SPGD algorithm is model-free, and thus is not strongly impacted by the presence of nonlinearities which degrade the performance of conventional phase reconstruction methods. Finally, for high energy laser applications, SPGD can be performed using the primary laser beam without the need for an additional beacon laser. The conventional SPGD algorithm was modified to use an adaptive gain to improve convergence while maintaining low steady state error. Results from laboratory experiments using phase plates as atmosphere surrogates will be presented, demonstrating areas in which the adaptive gain yields better performance and areas which require further investigation.
Deformable mirrors using polyvinylidene fluoride (PVDF) membranes in a bimorph configuration have been previously
investigated. Kratos Defense and Security Solutions, in partnership with Advanced Optical Systems, Inc. and NeXolve,
Inc., have been evaluating the utility of unimorph PVDF films for fabrication of deformable mirrors. Actuation using a
unimorph film is achieved by creating a gradient in the piezoelectric response of the film through a proprietary process.
This eliminates the requirement to bond multiple films and improves the optical quality of the films. To assist in the
development and design of the films, a multiphysics design tool has been developed by tightly integrating several
commercial software packages. This tool has then been used to model the performance of the films and extract
significant material parameters. This paper reports on the initial modeling results and characterization of this novel
material.
Deployable polarimetric imaging systems often use 2×2 arrays of linear polarizers at the pixel level to measure the
polarimetric signature. This architecture is referred to as a micro-grid polarizer array (MPA). MPAs are either bonded to
or fabricated directly upon focal plane arrays. A key challenge to obtaining polarimetric measurements of sub-pixel
targets using MPAs is registering the signals from each of the independent channels. Digital Fusion Solutions, Inc has
developed a micro-optic approach to register the fields of view of 2x2 subarrays of pixels and incorporated the device
into the design of a polarimetric imager. Results of the design will be presented.
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