Abacus Enterprises

Radiative transport/LIDAR/Remote sensing

The small angle approximation [SAA] to the radiative transport equation is widely used in predicting image quality for remote sensing applications. An investigation was undertaken to determine the range of applicability of the SAA. In the first set of experiments, various sizes of polystyrene spheres suspended in water were used as the scattering medium. The volume scattering function [VSF, sometimes called the scattering phase function] was calculated from the Mie theory and was measured directly. The VSF was then used as input to the SAA and the point spread functions [PSF] were calculated. The PSF's were measured for ranges of optical thickness from 1 to 10. Measured PSF's were then compared to those calculated from the SAA. In the second set of experiments, particle size distributions were constructed to mimic the VSF of sea water, based on Petzold's data. Results for both sets of experiments were the same: errors in the calculated and measured PSF's exceeded 10% for optical thicknesses greater than three.

I have worked extensively on the imaging models used for underwater mine hunting using LIDAR systems. I have also worked on a project to improve the capability to detect, classify, and localize underwater mines by removing the blur caused by wave action. Furthermore, I have worked on principle component analysis for a multispectral system designed to detect buried mines.

N.L. Swanson, B.D. Billard, V.M. Gehman, and T.L. Gennaro, "Application of the small angle approximation to ocean water types," Appl. Opt., 40, 3608-3613, 2001. >Abstract

N.L. Swanson, V.M. Gehman, B.D. Billard, and T.L. Gennaro, "Limits of the small angle approximation to the radiative transport equation," J. Opt. Soc. Am. A, 18, 385-391, 2001. Abstract

N.L.Swanson, "Mine detection laser technology model survey," CSS/TM-92/635, 1992.

N.L. Swanson, "Procedure for validation of Well's Multiple scattering theory," CSS/TN-92/1120, 1992.

N.L. Swanson, "Generic LIDAR model derivation," CSS/TM-91/580, 1991.

N.L. Swanson, "Model evaluation of the airborne electro-optics system for mine reconnaissance," CSS/TM-91/579, 1991.

Coherence properties of light scattered in random media

Investigation of how laser light is affected by particles randomly suspended in a medium such as smoke, fog, or water to determine ways to overcome the resulting distortion in images. A slight spectral broadening [few MHz] of the forward scattered light was measured for particles small compared to the wavelength and for particle mixtures containing small particles. This broadening results in a reduction of the temporal coherence of the scattered light. The broadening was attributed to scattering from coupled thermal and particle density fluctuations. Two patents were awarded.

N.L. Swanson, C.N. Pham, and D.H. VanWinkle, "Fringe visibility for multimode lasers: Gaussian and Lorentzian spectra," Appl. Opt., 36, 9509-9514, 1997. Abstract

N.L. Swanson and D.H. VanWinkle, "Forward scattered light: spectral broadening and temporal coherence," Phys. Rev. A, 55, 4501-4510, 1997. Abstract

N.L. Swanson and D.H. VanWinkle, "Effects of scattering on temporal coherence properties of laser light," APS annual meeting, 39, F16 13, March 1994.

D.H. VanWinkle and N.L. Swanson, "Rejection of white light noise using an interferometer," APS annual meeting, 39, G12 8,March 1994.

N.L. Swanson, Interoferometric Image Enhancement Device U.S. Patent no. 5680210, Oct. 21, 1997.

N.L. Swanson, "Heterodyne Filter for Image Enhancement,", U.S. Patent no. 5781298, Jul. 14, 1998.

Non-destructive testing/Remote sensing

Project for USAF to examine electro-optical techniques to remotely determine the condition of runway pavement during hostile situations. The various systems that were analyzed were: multispectral, hyperspectral, thermal, stereoscopic, polarimetry, scanning LIDAR, and beam fanning. A field test was undertaken to determine whether cracks and subsurface voids could be imaged with thermal cameras. The cameras were sensitive to the 1-6 micron and the 8-12 micron ranges. We found that the cracks and subsurface voids did show in the images but only during periods of heating and cooling [just after sunrise and sunset].

N.L. Swanson, H.W. Welker, B.T. Blume, and J.W. Rish III, "Application of thermal imaging to remote airfield assessment," Proc. SPIE, 3079, 819, 1997.

N.L. Swanson, V. Irwin, D. Marchette, "Electromagnetic remote sensing for airfield assessment," NSWCDD/TR-97/3, 1997.

Imaging

Multiple projects testing CCD cameras and image processing.

Project for USN calibrating Image Intensified CCD cameras made by Xybion.

Project for the Office of Naval Intelligence testing the response of a Kodak CCD camera to various laser and broadband sources.

Project for USN processing images for the Rapid Air Mine Countermeasures [RAMICS] project. Images were processed for detection and classification of underwater mines.