DETECTION OF THE SURFACE OF VENUS AT 1.0-MU-M FROM GROUND-BASED OBSERVATIONS

Thermal emission from the nightside of, Venus has been observed at 1.0 mu m during fall 1991 on the 1.05 m reflector at Pic-du-Midi. The ins trumental spectral response was centred in the 1.0 mu m window of the Venus atmosphere, located between strong absorptions of CO2. Synthetic calculations by a radiative transfer model of the atmosphere of Venus show that the atmosphere is transparent enough at these wavelengths t o allow a contribution from the surface to be transmitted through the clouds. The flux is sensitive to the surface temperature, which is con trolled by the altitude. Low flux features are observed on the disc, w hich are well correlated with the topographic maps of Magellan; these features do follow the solid rotation of the planet. An upper limit of about 10% can be put on the variations of the emissivity of the surfa ce at 1.0 mu m, in the Aphrodite Terra region where large radar emissi vity variations have been observed by Magellan.