PFS (the Planetary Fourier Spectrometer) covers the range 1.25 – 45 μm with spectral resolution about 2 cm−1 and angular resolution 0.035 – 0.070 rad (10 – 20 km on the Martian surface working at the periapsis). The instrument has two spectral channels: shortwavelength (SW) and longwavelength (LW) with a boundary near 5 μm. The photoconductive detector (PbSe) is used in the SW channel and the pyroelectric in LW channel. The main optical units of both channels are rotating interferometers with cubic mirror corner reflectors. The infrared radiation from Mars is directed to the interferometers by the pointing system that allows to observe selected points on the Martian surface. A “dichroic” plate splits the beam between LW and SW channels. Several hundred spectra will be obtained during one periapsis passage. These spectra will be used for investigation of Martian atmosphere (temperature and pressure vertical profiles, variations of small constituents such as H2O and CO, pressure near the surface, aerosol distribution, composition and optical depth) and some of surface properties (thermal, compositional, textural). Scientific facilities of six countries (Italy, Russia, Germany, Poland, France and Spain) cooperate in the work on this experiment.

Interpretation of Fourier-spectrometer experiment gave new knowledge about structure and variability of Venus atmosphere in the altitude range from 60 to 100 km during the time interval from 12 Oct to 14 Dec 1983. The very complex information content of IR-spectra made it possible for the first time to retrieve simultaneously temperature profile, optical cloud properties with hints to composition of upper cloud layer and cloud top altitude, SO2 and H2O mixing ratios, and search for unknown minor constituents. Basing on these results the whole radiation balance considering multiple-scattering by aerosol and exact gas transmittances (line by line) has been modelled. The gross-structure of meridional circulation (Hadley-cell) was estimated with these altitude and latitude dependent cooling and heating rates. From the retrieved temperature field the cyclostrophic wind with a jet of more than 100 m/s near 70 km altitude and 55° N has been computed. A linear barotropic model was developed to investigate these zonal wind profiles at 70 km altitude on instability of planetary waves. Wavenumber 2 has the greatest instability rate and a phase period in the range of 4 days. The barotropically most unstable disturbances have characteristics which are qualitatively in accordance with observed waves.

The temperature structure of the Venusian middle atmosphere derived from the Venera-15 Fourier spectrometer confirms in general previous investigations summarized in the Venus International Reference Atmosphere 1985. A detailed Fourier analysis of the temperature field in the solar fixed coordinate system shows generally a different behaviour for low (ϕ ≲ 50°) and high (ϕ ≳ 55°) latitudes, a predominance of wavenumber-2 with a full cl (360°) from the cloud top up to about 95 km at low latitudes and an anti-clockwise rotation of 180° at high latitudes. The amplitudes are, however, for both Fourier components less than 2 – 3 K. Larger amplitudes (> 4 K) are found at high latitudes in spectral intervals representing the upper cloud top, where wavenumber-1 is dominant. The maximum wavenumber-1 amplitude for the cloud top occurs at the morning terminator at high latitudes and around 2 p.m. at low latitudes.

Fourier spectrometers aboard the Venera 15 and 16 orbiters measured the outgoing spectral radiance of Venus in the 250–1600-cm−1 (Venera 15) and 400–1600-cm−1 (Venera 16) regions with a spectral resolution of 5–7 cm−1 depending on the data handling procedure. This paper gives a short description of the experimental design and discusses those aspects that can be suitably tackled by wide range spectral measurements. Different Venusian regions can be characterized by typical and significantly different radiance and brightness temperature spectra based on the magnitude of brightness temperatures and also on secondary spectral signatures caused by H2SO4 bands as well as isotopic and hot CO2 bands. At least five groups can be identified, one typical for equatorial regions, one for mid-latitudes, and three for the subpolar and polar regions. Estimates of H2O and SO2 abundances were obtained (∼30 ppm at 58 km and ∼2 ppm at 65 km, respectively). SO2 is first identified in the infrared by our measurements. A detailed comparison between computed and measured spectra for the transition zone between mid-latitudes and the cold subpolar region gives arguments that the cloud top is situated within the temperature inversion and not above or below it.