Vassili I. Moroz

Phobos: Spectrophotometry between 0.3 and 0.6 μm and IR-radiometry

A 0.3–0.6 (μm UV-visible spectrophotometer and a 5–50 μm radiometer in the KRFM experiment on Phobos 2 measured two groundtracks in the equatorial region of Phobos. Preliminary results indicate that three surface units can be recognized on the basis of differing UV-visible spectral reflectance properties. One of the units is most comparable spectrally to optically darkened mafic material, and a second is comparable either to anhydrous carbonaceous chondrite or to blackened mafic material. Spectral properties of the third unit do not resemble those of known meteorite types. Brightness temperatures measured by the radiometer are consistent with a typlcal surface thermal inertia of 1-3 x 10^(-3) cal/(cm^2) deg S^(1/2), as suggested by previous investigations, implying a lunar-like regolith texture. At least one area of possibly higher thermal inertia has been tentatively identified, where a large degraded crater is crossed by several grooves. These results indicate significant lateral heterogeneity in the optical and textural properties of Phoboss surface.

Characteristics of aerosol phenomena in Martian atmosphere from KRFM experiment data

Abstract Photometric limb-to-limb profiles of Mars were obtained in eight narrow bands between 315 and 550 nm from the Phohos 2 spacecraft. Tentative results of the analysis are presented in terms of optical properties of the atmosphere and surface. The imaginary part of the refraction index k from 0.01 to 0.03 for 315 nm and from 0.005 to 0.01 for 550 nm was estimated for the “constant” dust haze, using Mie theory for spherical particles. These values of k are a few times higher than obtained by laboratory tests of terrestrial analogues including basalt, andesit and montmorillonite. Two explanations are possible: influence of irregular shape of particles and/or the presence of some more absorbing substances (such as goethite). Particle sizes of a few tenths of micrometres having a refraction index of 1.55 are compatible with the discussed model of the “constant” haze. The full shape of the near equatorial photometric profile on 550 nm can be explained by the slightly absorbed atmosphere (with optical depth 0.4 and imaginary part of the refraction index 0.0075) above the moonlike (roughness factor q ≅ 0) surface. Icy particles with the same average sizes as in the haze ( r m = 0.4 μm ) but with more narrow size distribution can explain the bright spot above Arsia Mons. Optical depth τ ≅ 0.1 and column mass density 7·10 −5 g cm −2 of the icy clouds were evaluated.

Optical definition of the Planetary Fourier Spectrometer (PFS): an FTIR spectrometer for the Mars '96 mission

The PFS is optimized for studies for the Martian atmosphere and will be also used for investigations of the surface composition. The instrument is a dual Rotational Reflector Interferometer (RRI) and covers both the SWIR (1.25 - 4.5 micrometers ) and the MIR (5.6 - 40 micrometers ) in two channels. The Noise Equivalent Spectral Radiance (NESR) is predicted to characterize the instrument. The NESR depends of the modulation coefficient, the detectivity of the detectors, the other main parameters of the interferometer, and the spectral characteristics of filters and beamsplitters as well. The modulation coefficient takes into account both the most important deviations of the optical elements from the ideal ones and partial misalignment by mechanical tolerances. Typically estimated values are for the Short Wavelength Channel (LWC): 2 X 10-8 W/(cm2 sr cm-1) for (sigma) equals 400 cm-1 respective. Some extreme examples of the Martian surface are given where the recording of spectra is promising due to a satisfying signal to noise ratio and some other ones where measurements will be critically.

Studies of Martian atmosphere and surface by the Planetary Rourier Spectrometer on board the Mars-94 mission

The Planetary Fourier Spectrometer (PFS) on board the Mars-94 mission is an infrared spectrometer optimized for studies of the Martian atmosphere. Moreover, the measurements of the instrument also will provide information about the surface composition and the surface- atmosphere interactions. The spectrometer consists of a dual Rotational Reflector Interferometer (RRI) covering two spectral ranges 220 - 1670 cm-1 (6 - 45 micrometers ) and 2080 - 8000 cm-1 (1.25 - 4.8 micrometers ) the long wavelength channel (LWC) and the short wavelength channel (SWC) respectively. Partial misalignment due to tolerance effects of real optical and mechanical elements are taken into account in an estimation of the spectral responsivity in comparison with the radiation of the Martian surface and atmosphere.

Planetary Fourier spectrometer (PFS) for the MARS 94 mission

PFS is a two-channel Michelson interferometer operating in the infrared wavelengths between 1.25 and 45 micrometers . The instrument is mainly devoted to the study of the Martian atmosphere. The principal goals are the measurement of the atmospheric temperature and pressure, atmospheric constituents, aerosol and clouds, ground pressure for surface topography, and optical and thermophysical properties of the Martian soil. PFS will fly on the Mars 94 spacecraft which should be launched in 1994 and reach the planet in 1995. Essentially it consists of two different interferometers located in the same box which is divided in two parts. An edge filter placed on the PFS entrance is used to separate the spectral range into two parts. The reason for that is the different optical materials which have to be used in each spectral range. The optical layout of the experiment is very compact. Cubic mirrors are mounted on an L-structure pivoted on a stepping motor. The stepping motor moves the mechanics and permits the optical path difference between the arms to be varied. Each interferometer operates in a different spectral range between 1.25 - 4.8 micrometers (8000 - 2083 cm-1) and 6 - 45 micrometers (1666 - 220 cm-1), respectively. The spectral resolution is 2 cm-1. The entrance aperture area is 30 cm2 per channel and the field of view (FOV) 2 and 4 degs. Every measurement lasts about 4 s and the respective resolving power is 4166 and 1041. The time and, therefore, the relative optical path difference for the measurement of every point of the interferogram is given by a monochromatic reference channel at 1.2 micrometers which uses a laser diode as a source. The interferograms are double sided and have 16384 and 4096 points, respectively, corresponding to spectra of 6250 and 1823 points.