37th DPS Meeting, 4-9 September 2005
Session 45 Titan's Atmosphere
Poster, Wednesday, September 7, 2005, 6:00-7:15pm, Music Recital Room

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[45.10] Blurring in Titan's atmosphere

B. Grieger (MPI for Solar System Research), DISR Team

If a planet hosts an atmosphere, remote sensing of its surface is affected by light scattering. We can distinguish two effects: First, the direct beam from the surface is attenuated by absorption or by scattering out of the direct beam into other directions. Second, an atmospheric component is added. This consists of light that is scattered into the line of sight by the atmospheric volume elements along the line of sight. These volume elements are illuminated by the direct solar beam, by other atmospheric volume elements, and by the planet's surface.

In many remote sensing situations, it can be assumed that the atmospheric component does only depend on the average surface albedo and not on the local pattern in the vicinity of the point of view on the surface. Such situations can be treated with one-dimensional radiative transfer computations in the plane parallel approximation, for which effective algorithms like the doubling and adding method are available.

Under certain circumstances, substantial blurring can lead to unsharp contours like in a defocussed image (which is qualitatively different from a reduction of contrast). This situation can occur when the optical depth is not too far from unity, the particles in the atmosphere are stronly forward scattering, and the scatterers are to some extent confined to a layer between the target and the observer. Such situations can only be treated with fully three-dimensional radiative transfer computations.

We investigate the importance of blurring due to atmospheric scattering with three-dimensional radiative transfer computations for a series of idealized situations. The results are applied to Titan, where the images taken by the Cassini orbiter and the Huygens lander indicate the presence of blurring.

This work was supported by the German Aerospace Center (DLR), contract number 50 OH 98044.

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Bulletin of the American Astronomical Society, 37 #3
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