Measured Degree of Infrared Polarization for a Variety of Thermal Emitting Surfaces

Abstract

Approved for public release; distribution unlimited. ii REPORT DOCUMENTATION PAGEForm Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)June 2004 ARL-TR-3240 SPONSOR/MONITOR'S ACRONYM(S) 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) U.S. Army Research Laboratory 2800 Powder Mill Road Adelphi, MD 20783-1197 SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTES ABSTRACTWe report on a series of parametric measurements designed to measure the attenuative effects that surface roughness and aerosol contamination play in reducing polarized thermal surface emission. In particular, we measure the spectrally resolved linear degree of polarization (LDOP) for a series of roughened borosilicate (Pyrex 1 ) glass substrates as a function of roughness parameter, Ra, root mean square slope, m, and the angle of observation, θ. Spectrally resolved LDOP is measured over the waveband region 4 to13 µm by a modified Fourier transform IR spectrometer in which a wire-grid polarizer and an achromatic quarter-wave plate are used in conjunction to measure all four Stokes parameters. A second set of measurements is conducted on similar smooth glass substrates that are subjected to varying degrees of dew formation and aerosol contamination. Test substrates are oriented at a high grazing angle of 80 degrees and placed in a closed chamber. Dew or attenuative particulates, i.e., carbon black, potassium bromide, or pollen particles, are allowed to condense/settle on the thermal emitting surface while a band-averaged LDOP is recorded with a long-wave polarimetric IR imaging system. Measured results are then compared with predictive calculations based on a weighted Fresnel relation.

Real time polarization imaging of weld pool surface

“…The total emissivity  of thermal emissions is the mean value of the emissivities //  and   of thermal emissions with a polarization direction parallel and perpendicular to the plane of incidence, respectively. The emergence angle  is then inferred using the bijective relation [7]:…”

“…Shape-frompolarization methodology applied to thermal radiation emitted by a weld pool surface estimates the surface orientation from the polarimetric state of the emitted light, and subsequently provides a discrete gradient vector field for a discrete set of radiating points on object surfaces. The polarimetry of thermal emissions requires no external illumination and can deduce surface normals without ambiguous  values as the - relationship for thermal emissions is a bijective monotonically-increasing relationship [5][6][7]. Thermal emissions are infrared body emissions partially linearly polarized in the far field [8] in a direction parallel to the plane of incidence for objects large compared to the emitted wavelength.…”

IR polarimetric signatures

“…Thermal polarization is described in varying detail in the following references [6,7,8,9]. To understand the polarization signature of a surface it is instructive to develop the equations for polarized light emanating from a smooth surface.…”

Preliminary investigation of polarization effects during metal cutting

“…Surfaces, especially metal surfaces, can emit a significant amount of polarized light. When viewed on the macroscopic scale, this is often more pronounced for thermal radiation in the LWIR (long wave infrared, 8 μm to 12 μm wavelength) region than for the MWIR (mid-wave infrared, 3 μm to 5 μm wavelength) region [9,10] . MADMACS operates in the MWIR region.…”

“…MADMACS operates in the MWIR region. When viewed on the macroscopic scale, most surface features tend to scatter and depolarize emitted light [9,10] . However, viewing the surface on the macroscopic scale has the effect of averaging microscopic effects.…”