Galileo Infrared Imaging Spectroscopy Measurements at Venus

Abstract

During the 1990 Galileo Venus flyby, the Near Infaied Mapping Spectrometer investigated the night-side atmosphere of Venus in the spectral range 0.7 to 5.2 micrometers. Multispectral images at high spatial resolution indicate substanmial cloud opacity variations in the lower cloud levels, centered at 50 kilometers altitude. Zonal and meridional winds were derived for this level and are consistent with motion of the upper branch of a Hadley cell. Northern and southern hemisphere clouds appear to be markedly different. Spectral profiles were used to derive lower atmosphere abundances of water vapor and other species.

Venus looks different from day to night across wavelengths: morphology from Akatsuki multispectral images

“…They also suggest that although Belton et al (1991) inferred that dayside 0.986 µm contrasts correspond to about 55 km using the vertical wind shear, the contrasts could be located anywhere in the cloud from 48 to 70 km. Similarly, although Carlson et al (1991) attribute the 2.3 µm contrasts to 50 km, Takagi and Iwagami (2011) suggest that the contrasts may be located anywhere in the mid-or upper cloud region. Hueso et al (2015) attribute the cloud patterns between 0.3 and 1 µm to altitudes between 60 and 72 km and their near-infrared cloud motion measurements match those from the Pioneer Venus probe and VeGa balloon derived winds at altitudes between 56 and 62 km, differing from the 58-64 km level derived by ) from radiative calculations.…”

“…These two images are part of a ground-based campaign to collect supplemental images in support of the Akatsuki mission. Although the NIMS (Galileo) and VIRTIS (Venus Express) instruments also provided images at these wavelengths (Carlson et al 1991), the coverage was limited due to the flyby nature of Galileo observations for studying global morphology. VIRTIS obtained only limited coverage of the low latitudes and could not provide global views of the planet from an equatorial perspective due to the long integration time required for the spectral cubes and the elongated, polar orbit of Venus Express.…”

“…Galileo was the first spacecraft to map Venus between 0.7 and 5.2 µm from the near-infrared mapping spectrometer (NIMS) using the spacecraft spin and motion (Carlson et al 1991). The mapping channel of the visible infrared thermal imaging spectrometer (VIRTIS) also on Venus Express imaged the planet between 0.28 and 5.0 µm during April 15, 2006-November 27, 2014(Piccioni et al 2007a, and provided the widest spectral coverage of the southern polar hemisphere of Venus at low spatial resolution and limited coverage of the low southern and equatorial northern latitudes at higher spatial resolution (as high as a few hundred meters at periapsis).…”

Experiencing Venus: Clues to the origin, evolution, and chemistry of terrestrial planets via in-situ exploration of our sister world

“…In particular, nearinfrared maps in the 0.9-1.2-µm spectral range by VIRTIS on Venus Express are beginning to reveal in detail the spatial variability of thermal surface emission, due to variations in elevation and surface composition. As first discovered by Allen (1984) in groundbased observations and further revealed by the Galileo and Cassini flybys (Carlson et al, 1991;Baines et al, 2000), several useful spectral "windows" between CO 2 bands exist in the 0.9-1.2-µm range which allow thermal emission from Venus's hot (~ 740K) surface to be readily viewed under nighttime conditions wherein the strong glint from sunlit clouds is suppressed. The adiabatic lapse rate of 8K per km altitude ensures dramatic variations of surface thermal flux with elevation, as previously demonstrated by the flyby mapping of the Near Infrared Mapping Spectrometer (NIMS) on-board the Galileo spacecraft enroute to Jupiter (Carlson et al, 1991(Carlson et al, , 1993a and by ground-based observations (Lecacheux et al, 1993;Meadows and Crisp, 1996).…”

Initial products of Akatsuki 1-μm camera

“…On the nightside, there are several known IR windows that allow radiation to penetrate the clouds in the Venus atmosphere including 1.0-1.3-, 1.7-and 2.3-μm regions (Carlson et al 1991). The 1.0-1.3-μm window has mostly been used for investigating surface properties.…”