Venus's Thermal Environment

extracted from Thermal Environments JPL D-8160


Link to: JPL data or GSFC data

The following table summarizes the range of Direct Solar, Reflected Solar (Albedo), and Planetary Infrared for the planet Venus.


                 Perihelion       Aphelion         Mean
----------------------------------------------------------------
Direct Solar      2650 W/sqM      2579 W/sqM      2614 W/sqM

Albedo             0.8+/.02        0.8+/-.02       0.8+/-.02
(subsolar peak)

Planetary IR.       153 W/sqM        153 W/sqM       153 W/sqM


The albedo of Venus is very high and results in a thermal environment for a spacecraft at the subsolar point of some 3.6 solar constants (~2 on the sunlit side and 1.6 on the Venus side). The cloud system results in some backscattering effects at large incident solar zenith angles which create some limb brightening. For low altitude orbits, modeling the Venusian reflected solar term as diffuse with a cosine fall-off is fairly accurate. In fact, at the subsolar point, this assumption is slightly conservative for altitudes up to about 1700 km (0.28 Venus Radii).

For higher altitudes, the limb brightening becomes more prevalent, thus the diffuse assumption can be unconservative by about 10% at an altitude of 6100 km (1 Venus Radii) and up to 41% at very large altitudes. The energy levels associated with this unconservatism may not be particularly significant due to the dominance of direct solar irradiance at such altitudes. For particularly sensitive instruments, a full evaluation of the Venusian bi-directional characteristic at each orbital position is recommended.

Even though the surface temperatures approach 750K, the planetary infrared term is not particularly large. In fact it is significantly less than that for Earth. This is due to the trapping of the surface infrared by the cloud system which is not transparent to infrared. This results in a fairly uniform planetary infrared term as shown below which represent the variation with latitude.

     Venus Planetary Infrared Emission
  -----------------------------------------------
   Latitude     Emission Flux W/sqM     T. K
  -----------------------------------------------
     0-10             146.3            225.4
    10-20             153.4            228.1
    20-30             156.7            229.3
    30-40             158.7            230.0
    40-50             155.5            228.9
    50-60             152.0            227.5
    60-70             138.5            222.3
    70-80             143.5            224.3
    80-90             178.4            236.8


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