Spatially-Resolved 1.6µm Spectroscopy of Titan

Máté Ádámkovics, Imke de Pater, Henry G. Roe, Seran G. Gibbard, and Caitlin A. Griffith

Department of Chemistry - University of California, Berkeley, CA 94720
(510) 642-4499

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For a detailed description with references please read our submitted manuscript.

The vertical structure of Titan's atmosphere and surface composition can be probed spectroscopically and usually involves integrating data over the entire disk. Spatial variations in surface contrast, atmospheric haze and clouds can be measured by adaptive optics imaging with narrowband filters. Below are results combining these two techniques. With spatially-resolved spectroscopy the atmospheric structure and surface albedo can be determined at various locations on the disk of Titan. These data have been particularly useful in determining the magnitude and altitude of the seasonal enhancement of tropopause haze near the Southern pole.

Below is a map of Titan at a wavelength that is sensitive to the surface, constructed from NIRSPEC/AO observations made on 20 February 2001 UT at W.M. Keck Observatory. Click on the image to see a visualization of how the image of the disk changes as a function of wavelength. Images from 1.5 - 1.7µm probe from the surface up to above 150km in the atmosphere. Images at increasing wavelengths (particulary in the 1.58 - 1.65µm range) are analagous to what would be seen travelling up through the atmosphere from the surface, plowing through the tropopause, and into the lower stratosphere -- which extends upwards to 500km. The movie above shows a trip through Titan's lower atmosphere. Some things to look for in the movie are the variations in albedo throughout regions that probe the surface, then the striking change near 1.6µm, when the tropopause (cirrus) haze in the Southern hemisphere dominates the contrast, and then the stratospheric haze asymetries, which include the East-West limb brightenning and the North-South haze asymetry.

Click on the image to see mpeg movie (3.3Mb)

The figure below shows the same images reconstructed from individual spectra as seen above (left), along with the spectrum at the center of the disk (center), and the disk-integrated temperature profile (right). The vertical blue line on the spectrum indicates the wavelength of the image seen at the left, and the horizontal blue line on the temperature profile shows the altitude probed that is probed.

Click on the image to see mpeg movie (3.3Mb)

This dataset allows for the direct quantitative measurement of the 3-dimensional haze distribution from the surface to the stratosphere. Upcoming research will involve writing the algorithms for efficient modelling of the data with radiative transfer code -- as performed for selected points from this dataset in our current manuscripts, for use in analysis of datasets that will be aquired with field-integral spectrometers such as SPIFFI and OSIRIS.

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(last updated 04 April 14)