HR: 08:45h
AN: P41B-04 [Abstracts]
TI: Ranging to the Venus Atmosphere With the Mercury Laser Altimeter
AU: * Smith, D E
EM: dsmith@tharsis.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD
20771, United States
AU: Zuber, M T
EM: zuber@mit.edu
AF: Massachusetts Institute of Technology, Dept Earth, Atmospheric and Planetary Sciences,
Cambridge, MA 02139, United States
AU: Neumann, G A
EM: neumann@tharsis.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD
20771, United States
AU: Sun, X
EM: xsun@pop900.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD
20771, United States
AU: Cavanaugh, J F
EM: John.F.Cavanaugh@nasa.gov
AF: NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD
20771, United States
AU: McGarry, J
EM: Jan McGarry
AU: Solomon, S C
EM: scs@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington
5421 Broad Branch Road, Washington, DC 20015, United States
AB:
During the flyby of Venus on 05 June 2007 by the MESSENGER spacecraft the Mercury Laser Altimeter (MLA) was
operated for approximately 30 minutes, including approximately 8 minutes within 800 km of the planet's surface.
With almost no expectation of receiving a return from the Venus surface the altimeter was targeted at the Venus
atmosphere between 40 and 80 km above the surface, the altitude range of thickest clouds. Previous
observations of the Venus atmosphere from nephelometry and particle size spectrometry indicated a structure of
the clouds consisting of a haze that increases in opacity with depth, without discrete cloud tops. An objective of
the MLA experiment was to attempt to identify heretofore undetected layering within the upper part of the Venus
cloud deck. Although the MLA is a ranging device and not an atmospheric lidar, an instrument of similar design
on the Mars Global Surveyor (MGS) spacecraft had obtained clear returns from layers within the Martian
atmosphere at altitudes up to several tens of kilometers above the surface.
At Venus, the MLA operated successfully in science ranging mode for the first time; the instrument recorded
photon counts throughout the period of operation. We analyzed in detail a period of approximately 3 minutes
when the spacecraft was closest to the planet at less than 400 km and when returns from the atmosphere would
be most likely. When the backscattered signal is weak or non-existent, the altimeter dark noise dominates the
detector count. Returns from cloud layers, if they exist, would appear as increased detector counts at the altitude
of the cloud layer on top of the detector noise. The altimeter returns indicate a significant noise component
throughout the 8-minute period of operation, including the 3 minutes bounding closest approach. Analysis of the
data by three different methods suggest an increase in returns in two regions between 50 and 70 km altitude
range, which, on the basis of statistical analysis, could be attributable to backscattered photons from the Venus
atmosphere at a weak level of statistical significance. However, the experiment showed no evidence for discrete
layering within the primary cloud deck.
DE: 6295 Venus
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting