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Near-infrared (0.67-4.7 micron) Optical Constants Estimated for MontmorilloniteVarious models of the reflectance from particulate surfaces are used for interpretation of remote sensing data of solar system objects. These models rely upon the real (n) and imaginary (k) refractive indices of the materials. Such values are limited for commonly encountered silicates at visual and near-infrared wavelengths (lambda, 0.4-5 micron). Availability of optical constants for candidate materials allows more thorough modeling of the observations obtained by Earth-based telescopes and spacecraft. Two approaches for determining the absorption coefficient (alpha=2 pi k/lambda) from reflectance measurements of particulates have been described; one relies upon Kubelka-Munk theory and the other Hapke theory. Both have been applied to estimate alpha and k for various materials. Neither enables determination of the wavelength dependence of n, n=f(lambda). Thus, a mechanism providing this ability is desirable. Using Hapke-theory to estimate k from reflectance measurements requires two additional quantities be known or assumed: 1) n=f(lambda) and 2) d, the sample particle diameter. Typically n is assumed constant (c) or modestly varying with lambda; referred to here as n(sub 0). Assuming n(sub 0), at each lambda an estimate of k is used to calculate the reflectance and is iteratively adjusted until the difference between the model and measured reflectance is minimized. The estimated k's (k(sub l)) are the final results, and this concludes the typical analysis. Additional information is included in the original extended abstract.
Document ID
20050182106
Acquisition Source
Headquarters
Document Type
Preprint (Draft being sent to journal)
Authors
Roush, T. L.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2005
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: Lunar and Planetary Science Conference
Location: Houston, TX
Country: United States
Start Date: March 13, 2005
End Date: March 18, 2005
Funding Number(s)
OTHER: UPN 21-344-30-1R
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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