Physics – Optics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2904e&link_type=abstract
American Astronomical Society, DPS meeting #40, #29.04; Bulletin of the American Astronomical Society, Vol. 40, p.443
Physics
Optics
Scientific paper
The Cassini Composite Infrared Spectrometer (CIRS) FP1 channel is a polarizing interferometer covering the spectral range from 10 to 600 cm-1. For Saturn's rings, thermal radiation at these wavelengths can be broken down into the product of a single temperature Planck function, a geometric filling factor, and the emissivity. We examine two aspects of the emissivity in this paper: spectral variability and polarization.
A decrease in the emissivity at 100 cm-1 reveals that its wavelength dependence is non-grey with deviation from a constant between 150 cm-1 and 300 cm-1. A broad spectral feature near 225 cm-1 and the absence of a feature near 160 cm-1 may indicate the presence of amorphous water ice in the B-ring (e.g. Curtis, et al., Applied Optics, 44, 4102-4118, 2005). In this second look at the spectrum, we use various emissivity theories to determine whether this in fact true or if crystalline ice features are simply muted in emission.
Rotating its optical axis, we measure the IR polarization over the FP1 spectral range with dedicated several long sit-and-stare observations of the lit and unlit sides of the A-, B-, and C-rings. In all cases, the FP1 field of view was rotated to relative angles of 0º, 30º, and 60º. For each ring, we have determined the Stokes Vector (I, Q, U, V) and the degree of polarization, (Q+U+V)/I. We examine the degree to which the measured temperature and emissivity varies with the orientation of the field of view and illustrate the constraints that could be placed on the microscopic roughness of ring particles and/or large-scale ring structures.
The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Edgington Scott G.
Jennings Donald E.
Leyrat Cedric
Nugent Carolyn R.
Pearl John C.
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