Emittance measurement study

Directional spectral emittance of black body cavitie

A Study of Bi-Directional Reflectance Distribution Functions and Their Effects on Infrared Signature Models

Since 2004, AFIT has been developing a trend-analysis tool to assess large commercial aircraft infrared (LCAIR) signatures. In many cases, this code predicted signatures to within 10% of measured data. However, other results indicated that the single-bounce, specular-reflection algorithm being used failed to adequately simulate interactions between aircraft parts where either the specular component is dominated by diffuse reflection or part-to-part multiple-bounce reflections contribute significantly to the signature. This research incorporates Bi-Directional Reflectance Distribution Functions (BRDF\u27s) and multiple-bounce calculations into the LCAIR model. A physical aircraft model was constructed from aluminum, and measurements were taken before and after a surface treatment in gloss black paint. The Sandford-Robertson model is used to parameterize the BRDF\u27s of both the bare aluminum and gloss black paint. Since the most efficient method of integrating a BRDF depends upon the reflectance distribution of the aircraft material, the sampling resolution of the BRDF integral is crucial to an accurate simulation. Additionally, care is taken to ensure that the integration of the hemispherical irradiance onto each facet of the computational model is sampled at a sufficient resolution to achieve convergence in the solution. Simulations in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) bands validate both the previous specular reflectance simplification for the gloss black simulations and the failure of the previous algorithm for the highly reflective bare aluminum. The necessity of considering multiple bounces in the simulation is also demonstrated amongst part-to-part reflections near the wing root, where three or four bounces are required for the solution to converge. Finally, three scenarios simulating a man-portable air defense system (MAN-PADS) system engaging an Airbus A340-300 aircraft landing at a generic airport are performed

Photometric stereo for strong specular highlights

Photometric stereo (PS) is a fundamental technique in computer vision known to produce 3-D shape with high accuracy. The setting of PS is defined by using several input images of a static scene taken from one and the same camera position but under varying illumination. The vast majority of studies in this 3-D reconstruction method assume orthographic projection for the camera model. In addition, they mainly consider the Lambertian reflectance model as the way that light scatters at surfaces. So, providing reliable PS results from real world objects still remains a challenging task. We address 3-D reconstruction by PS using a more realistic set of assumptions combining for the first time the complete Blinn-Phong reflectance model and perspective projection. To this end, we will compare two different methods of incorporating the perspective projection into our model. Experiments are performed on both synthetic and real world images. Note that our real-world experiments do not benefit from laboratory conditions. The results show the high potential of our method even for complex real world applications such as medical endoscopy images which may include high amounts of specular highlights

Thermophotovoltaic space power system, phase 3

Work performed on a research and development program to establish the feasibility of a solar thermophotovoltaic space power generation concept was summarized. The program was multiphased. The earlier work is summarized and the work on the current phase is detailed as it pertains to and extends the earlier work. Much of the experimental hardware and materials development was performed on the internal program. Experimental measurements and data evaluation were performed on the contracted effort. The objectives of the most recent phase were: to examine the thermal control design in order to optimize it for lightweight and low cost; to examine the concentrator optics in an attempt to relieve pointing accuracy requirements to + or - 2 degrees about the optical axis; and to use the results of the thermal and optical studies to synthesize a solar thermophotovoltaic (STPV) module design that is optimized for space application

Impact of Metallic Interface Description on Sub-wavelength Cavity Mode Computations

17 pagesWe present a numerical study of electromagnetic reflection and cavity modes of 1D-sub-wavelength rectangular metallic gratings exposed to TM-polarized light. Computations are made using the modal development. In particular we study the influence of the choice of boundary conditions on the metallic surfaces on the determination of modes, on specular reflectance and cavity mode amplitudes. Our full real-metal approach shows some advantages when compared to former results since it is in better accordance with experimental results

A preliminary assessment of small steam Rankine and Brayton point-focusing solar modules

A preliminary assessment of three conceptual point-focusing distributed solar modules is presented. The basic power conversion units consist of small Brayton or Rankine engines individually coupled to two-axis, tracking, point-focusing solar collectors. An array of such modules can be linked together, via electric transport, to form a small power station. Each module also can be utilized on a stand-alone basis, as an individual power source

Directional Thermal Emission and Absorption from Surface Microstructures in Metalized Plastics

Thermal emission, exhibiting antenna-like directivity, has been generated by a wide variety of both simple and complex micro-structures. The basic demonstrations of directional emission, and specific device performance evaluations, have been conducted at elevated temperatures, typically several hundred degrees Celsius. The most common applications for these high-temperature designs are thermal photo-voltaic and spectroscopic sources. A wide range of lower temperature applications, such as spacecraft thermal management and mid- to far-infrared optical train stray light management, are precluded by the cost and complexity of the fabrication processes employed. In this work, a novel fabrication and physical surface optimization of a seminal directionally emitting structure is conducted in metalized plastic. The fabrication method is derived from the high-throughput compact disc manufacturing process and exploits the advantageous surface electromagnetic properties of aluminium, at the expense of forgoing high-temperature operation. Then, a novel directionally emitting structure, exhibiting a broader angular response, is design and fabricated by the same methods. The performance of both structures is evaluated through reflectance and self-emission measurements, and compared to rigorous modeling results. The necessity of conducting low-temperature emission and reflectance measurements, on instruments designed for radiometry rather than scatterometry, requires consideration of the longitudinal spatial coherence of field incidence on the surface. To this end, a well-developed modeling method was extended to include finite longitudinal spatial coherence excitation

Isotropic and Anisotropic Interfaced Lambertian Microfacets

Specular microfacet distributions have been successfully employed by many authors for representing materials glossiness, and they are generally combined with a Lambertian term that accounts for the colored aspect. Such a representation makes use of the Fresnel reflectance factor at the interface, but the transmission factor is often ignored. In addition, the generalization to microfacet distributions with a more general reflectance is known to be complex, since it requires to solve an angular integral that has no analytical solution. This paper proposes a complete framework for physically handling both reflection and transmission with microfacet distributions. First, we show how transmission affects reflectance of an interfaced Lambertian model, and provide an analytical description of an individual microfacet reflectance. Second, we describe a method for handling distributions of such microfacets in any physically based Monte-Carlo rendering systems. Our approach generalizes several previous models, including flat Lambertian materials as well as specular and Lambertian microfacets. The result section illustrates the wide range of materials that can be possibly taken into account with this representation

An experimental and analytical study of visual detection in a spacecraft environment, 1 July 1968 - 1 July 1969

Predicting star magnitude which can be seen with naked eye or sextant through spacecraft windo