Accession Number : ADA464331


Title :   A Study of Bi-Directional Reflectance Distribution Functions and Their Effect on Infrared Signature Models


Descriptive Note : Master's thesis


Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT/DEPT OF ENGINEERING PHYSICS


Personal Author(s) : Harkiss, Samuel I


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a464331.pdf


Report Date : Mar 2007


Pagination or Media Count : 153


Abstract : 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's) 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's 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.


Descriptors :   *INFRARED SIGNATURES , *AIRCRAFT SIGNATURES , *REFLECTANCE , COMMERCIAL AIRCRAFT , INFRARED RADIATION , DISTRIBUTION FUNCTIONS , THESES , INFRARED IMAGES , COMPUTER GRAPHICS


Subject Categories : Civilian Aircraft
      Cybernetics
      Infrared Detection and Detectors
      Optics


Distribution Statement : APPROVED FOR PUBLIC RELEASE