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[44.02] Near-IR and Visible Wavelength Imaging from a Venus Descent Vehicle

M. A. Bullock (Southwest Research Institute), D. Crisp (Jet Propulsion Laboratory), B. A. Campbell (Smithsonian Institution), R. Greeley (Arizona State University)

Near-IR and visible imaging from a descent vehicle to the surface of Venus presents a number of unique scientific challenges and opportunities. Magellan radar images typically have a resolution of 200 m. The Venera lander cameras produced tantalizing close-up views of the surface, out to a few 10's of meters from their vehicles. Visible and/or near-IR images from a descent vehicle could provide the much-needed context to understand the information at these disparate scales. In particular, the possibility exists to compare visible and near-IR imagery directly with Magellan radar images at a similar scale, and to extrapolate these comparisons to much of the global Magellan dataset. Even a handful of visible and near-IR images from a Venus descent vehicle therefore has the potential of ushering in a new era of geological interpretation.

Due to the dense CO₂ atmosphere, Rayleigh scattering precludes clear images at visible wavelengths above about 10 km. The 0.5 \mum Rayleigh scattering optical depth between the clouds and surface (48 km) is ~25, but it is ~1 at 1.0 \mum. Due to the increased Rayleigh scattering optical depth at off-nadir angles, the field of view is limited. Spacecraft motion is also critical in descent imaging. Zonal winds decrease approximately linearly from about 75 m/s just beneath the clouds to zero at the surface. The ability to acquire nested images is therefore constrained by the widening field of view and decreasing horizontal velocity, with decreasing altitude.

We have developed a set of coupled differential equations that describe the field and center of view of a Venus descent camera as a function of altitude. We will describe the scope of imaging observations that are possible from a vehicle descending to the surface of Venus.

This work has been supported by NASA's Planetary Atmospheres Program and NSF Planetary Astronomy.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.