[SIO GP Seminars] Howard Zebker, Stanford U. April 27, Friday

[Matt Wei]

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FRIDAY, Apr. 27, 3:00 PM
(refreshments served at 2:45 PM)
Munk Conference Room

Howard Zebker
Stanford University

"Titan’s Surface from Reconciled Cassini Microwave Reflectivity and  
Emissivity Observations"

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Abstract:

The surface of Titan, Saturn’s largest moon, appears to consist of  
solid hydrocarbon or CO2 ices with considerable small-scale  
structure, according to an electromagnetic scattering model that  
incorporates both radar reflectivity and emissivity measurements from  
the Cassini spacecraft. Our model resolves a well-known ambiguity in  
active and passive observations of surfaces, namely that the  
dielectric constant retrieved from radiometric data is usually less  
than that obtained from radar backscatter analysis. We present here a  
method that predicts both radar and radiometric surface responses  
from a single set of physical parameters, which we use to invert the  
Cassini RADAR data. The dielectric constant of the observed areas  
ranges from 1.85-2.5, consistent with the ices listed above, but also  
consistent with unconsolidated water or ammonia ice. We include both  
surface and volume scattering mechanisms in the model and find that  
the majority of the backscattered radar energy results from volume,  
rather than surface, scattering processes. This implies that  
variations in radar brightness and in emitted microwave signals are  
mainly diagnostic of composition and structure within Titan’s near  
sub-surface. In fact, the high level of volume scatter and consequent  
high radar albedo suggest that there is significant wavelength-scale  
structure and multiple scatter within the medium. This is most  
consistent with a surface composed either of ubiquitous mm-size  
bubbles within the ice, analogous to an aa cryolava, or structures  
similar to ice pipes and lenses found in terrestrial ice sheets. The  
cryovolcanic hypothesis suggests planet-wide resurfacing by active  
volcanism to explain the large-scale uniformity of observed  
backscatter. If the lens/pipe mechanism pertains, it can imply  
percolation of precipitating liquid or surface melt through the Titan  
“firn.”

Have a good day.

Matt

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Meng Wei ( Matt )
Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, CA 92093-0225
mwei at ucsd.edu
(858) 822-4347
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