From the article New: Hot Map of Venus, that I found in this answer:
VIRTIS looked through the thick carbon dioxide curtain surrounding Venus and detected the heat directly emitted by the hot rocks on the ground. The instrument made use of the so-called infrared spectral "windows" present in the Venusian atmosphere. Through these windows thermal radietion at specific wavelengths can leak from the deepest atmospheric layers, pass through the dense cloud curtain, and then escape to space, where it can be detected.
(Emphasis by me)
This can be confirmed by some passages from the article Venus Atmospheric Thermal Structure and Radiative Balance:
At wavelengths of 0.8-2.4 $\mu$m, the H$_2$SO$_4$ clouds are translucent. Aerosols are almost non-absorbing and their scattering properties have little variability with wavelength. The altitude of the origin of the night side emission is wavelength dependent and varies from the very surface at 1$\mu$m to ~35 km at 2.3 $\mu$m.
The lower atmosphere is opaque at infrared wavelengths, with CO$_2$ being the principal source of absorption at wavelengths near 2.0, 2.7, 4.3, 4.8, 5.2, and 15 $\mu$m.
H$_2$O also absorbs in the 2.2-2.5 $\mu$m range. Furthermore, the water vapor detected at this wavelength is from just below the clouds, while H$_2$O absorption at 1-1.2 $\mu$m comes from the atmosphere immediately above the surface.
(Emphases by me)
These passages show, with other absorption wavelengths mentioned in the article, that in the infrared spectrum shown in Fig. 31, the emission at 1 $\mu$m comes from the very surface !