Vertical Properties of the Global Haze on Titan Deduced from Methane Band Spectroscopy Between 7100 and 9200 Å

Details Vertical Properties of the Global Haze on Titan Deduced from Methane Band Spectroscopy Between 7100 and 9200 Å Vertical Properties of the Global Haze on Titan Deduced from Methane Band Spectroscopy Between 7100 and 9200 Å

Jun 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jkas...41...65s&link_type=abstract

Journal of the Korean Astronomical Society, vol. 41, no. 3, pp. 65-76

Astronomy and Astrophysics

Astronomy

4

Titan: Atmosphere, Titan: Haze, Visible Range, Spectroscopy

Scientific paper

We have investigated the optical properties of the global haze on Titan from spectra recorded between 7100 and 9200 Å, where CH_{4} absorption bands of various intensities occur. The Titan spectra were obtained on Feb. 23, 2005 (UT), near the times of the Cassini T3 flyby and Huygens probe, using an optical echelle spectrograph (BOES) on the 1.8-m telescope at Bohyunsan Observatory in Korea. In order to derive the optical properties of the haze as a function of altitude, we developed an inversion radiative-transfer program using an atmospheric model of Titan and laboratory CH_{4} absorption coefficients available from the literature. The derived extinction coefficients of the haze increase toward the surface, and the coefficients at shorter wavelengths are greater than those at longer wavelengths for the 30 - 120 km altitude range, indicating that the Titanian haze becomes optically thin toward the longer wavelength range. Total optical depths of the haze are estimated to be 1.4 and 1.2 for the 7270 - 7360 Å and 8940 - 9150 Å ranges, respectively. Based on the Huygens/DISR data set, Tomasko et al. (2005) reported total optical depths of 2.5 - 3.5 at 8290 Å, depending on the assumed fractal aggregate particle model. The total optical depths based on our results are smaller than those of Tomasko et al., but they partially overlap with their results if we consider a large uncertainty from possible variations of the CH_{4} mixing ratio over Titan's disk. We also derived the single scattering albedo of the haze particles as a function of altitude: it is less than 0.5 at altitudes higher than ˜150 km, and approaches 1.0 toward the surface. This behavior suggests that, at altitudes above ˜150 km, the average particle radius is smaller than the wavelengths, whereas near the surface, it becomes comparable or greater.

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