Martian Aerosols Research Articles

Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 1. Methodology and Application to the MY 34 Global Dust Storm

AbstractSince the beginning of the Trace Gas Orbiter (TGO) science operations in April 2018, its instrument “Nadir and Occultation for MArs Discovery” (NOMAD) supplies detailed observations of the IR spectrums of the Martian atmosphere. We developed a procedure that allows us to evaluate the composition and distribution's parameters of the atmospheric Martian aerosols. We use a retrieval program (RCP) in conjunction with a radiative forward model (KOPRA) to evaluate the vertical profile of aerosol extinction from NOMAD measurements. We then apply a model/data fitting strategy of the aerosol extinction. In this first article, we describe the method used to evaluate the parameters representing the Martian aerosol composition and size distribution. MY 34 GDS showed a peak intensity from LS 190° to 210°. During this period, the aerosol content rises multiple scale height, reaching altitudes up to 100 km. The lowermost altitude of aerosol's detection during NOMAD observation rises up to 30 km. Dust aerosols reff were observed to be close to 1 μm and its νeff lower than 0.2. Water ice aerosols reff were observed to be submicron with a νeff lower than 0.2. The vertical aerosol structure can be divided in two parts. The lower layers are represented by higher reff than the upper layers. The change between the lower and upper layers is very steep, taking only few kilometers. The decaying phase of the GDS, LS 210°–260°, shows a decrease in altitude of the aerosol content but no meaningful difference in the observed aerosol's size distribution parameters.

LIDAR for Investigation of the Martian Atmosphere from the Surface

The lidar device as part of the meteorological complex of the ExoMars-2022 landing platform is designed to study Martian aerosol, the planetary boundary layer, and small-scale atmospheric turbulence. A miniature lidar based on a pulsed semiconductor laser and an avalanche photodiode in the photon counting mode will make it possible to obtain aerosol backscattering profiles along a vertical path from 10 to 1500 m during the day and from 15 to 10 000 m at night. In the passive mode, the sky brightness is measured in a narrow spectral range and in a narrow solid angle with a frequency of up to hundreds of hertz. The measured fluctuations can provide information about the turbulence of the daytime atmosphere and its relation to dust activity. In the paper we considered the scientific tasks of the experiment, the program of measurements on the surface of Mars and described in detail the components of the equipment and the features of their work.

LIDAR for Investigation of the Martian Atmosphere from the Surface

The lidar device as part of the meteorological complex of the ExoMars-2022 landing platform is designed to study Martian aerosol, the planetary boundary layer, and small-scale atmospheric turbulence. A miniature lidar based on a pulsed semiconductor laser and an avalanche photodiode in the photon counting mode will make it possible to obtain aerosol backscattering profiles along a vertical path from 10 to 1500 m during the day and from 15 to 10000 m at night. In the passive mode, the sky brightness is measured in a narrow spectral range and in a narrow solid angle with a frequency of up to hundreds of hertz. The measured fluctuations can provide information about the turbulence of the daytime atmosphere and its relation to dust activity. In the paper we considered the scientific tasks of the experiment, the program of measurements on the surface of Mars and described in detail the components of the equipment and the features of their work.

Properties of Water Ice and Dust Particles in the Atmosphere of Mars During the 2018 Global Dust Storm as Inferred From the Atmospheric Chemistry Suite

AbstractThe properties of Martian aerosols are an integral part of the planetary climatology. Global dust storms (GDS) significantly alter spatial and vertical distributions of dust and water ice aerosols and their microphysical properties. We explored the 2018/Martian year 34 GDS with the Atmospheric Chemistry Suite instrument onboard the ESA‐Roscosmos Trace Gas Orbiter mission. Solar occultation observations of thermal infrared and near infrared channels in the 0.7–6 μm spectral range with >103 signal‐to‐noise ratio are used to constrain the vertical dependence and the temporal evolution of the particle properties of water ice and dust (effective radius, effective variance, number density, and mass loading) before the 2018 GDS and during its onset and decay phases. In most of the observations, the particle size of dust and water ice decreases with altitude. The effective radius of dust and water ice particles ranges in 0.1−3.5 μm and 0.1–5.5 μm, respectively. The largest aerosol particles (> 2.5 μm for dust and > 3.5 μm for water ice) are present below 10 km before the onset and during the GDS decay phase. During the peak of the GDS, dust reached altitudes of 85 km; the most frequently observed effective radius is 1–2 μm with 0.1–1 cm−3 number density and 0.1 effective variance. Detached layers of water ice composed of 0.1–1 μm particles are systematically observed at 50–100 km during this period. Below, at 0–50 km, we see the dust mixed with the main water ice layer comprising 1–4 μm particles.

Martian airfall dust on smooth, inclined surfaces as observed on the Phoenix Mars Lander telltale mirror

The telltale mirror, a smooth inclined surface raised over 1m above the deck of the Phoenix Mars Lander, was observed by the Surface Stereo Imager (SSI) several times per sol during the Phoenix Mars Lander mission. These observations were combined with a radiative transfer model to determine the thickness of dust on the wind telltale mirror as a function of time. 239 telltale sequences were analyzed and dustiness was determined on a diurnal and seasonal basis. The thickness of accumulated dust did not follow any particular diurnal or seasonal trend. The dust thickness on the mirror over the mission was 0.82±0.39µm, which suggests a similar thickness to the modal scattering particle diameter. This suggests that inclining a surface beyond the angle of repose and polishing it to remove surface imperfections is an effective way to mitigate the accumulation of dust to less than a micron over a wide range of meteorological conditions and could be beneficial for surfaces which can tolerate some dust but not thick accumulations, such as solar panels. However, such a surface will not remain completely dust free through this action alone and mechanical or electrical clearing must be employed to remove adhered dust if a pristine surface is required. The single-scattering phase function of the dust on the mirror was consistent with the single-scattering phase function of martian aerosol dust at 450nm, suggesting that this result is inconsistent with models of the atmosphere which require vertically or horizontally separated components or broad size distributions to explain the scattering behavior of these aerosols in the blue. The single-scattering behavior of the dust on the mirror is also consistent with Hapke modeling of spherical particles. The presence of a monolayer of particles would tend to support the spherical conclusion: such particles would be most strongly adhered electrostatically.

Minerals detection for hyperspectral images using adapted linear unmixing: LinMin

Minerals detection over large volume of spectra is the challenge addressed by current hyperspectral imaging spectrometer in Planetary Science. Instruments such OMEGA (Mars Express), CRISM (Mars Reconnaissance Orbiter), M3 (Chandrayaan-1), VIRTIS (Rosetta) and many more, have been producing very large datasets since one decade. We propose here a fast supervised detection algorithm called LinMin, in the framework of linear unmixing, with innovative arrangement in order to treat non-linear cases due to radiative transfer in both atmosphere and surface. We use reference laboratory and synthetic spectral library. Additional spectra are used in order to mimic the effect of Martian aerosols, grain size, and observation geometry discrepancies between reference and observed spectra. The proposed algorithm estimates the uncertainty on “mixing coefficient” from the uncertainty of observed spectra. Both numerical and observational tests validate the approach. Fast parallel implementation of the best algorithm (IPLS) on Graphics Processing Units (GPU) allows to significantly reduce the computation cost by a factor of ∼40.

Retrieving atmospheric dust opacity on Mars by imaging spectroscopy at large angles

We propose a new method to retrieve the optical depth of Martian aerosols (AOD) from OMEGA and CRISM hyperspectral imagery at a reference wavelength of 1μm. Our method works even if the underlying surface is completely made of minerals, corresponding to a low contrast between surface and atmospheric dust, while being observed at a fixed geometry. Minimizing the effect of the surface reflectance properties on the AOD retrieval is the second principal asset of our method. The method is based on the parametrization of the radiative coupling between particles and gas determining, with local altimetry, acquisition geometry, and the meteorological situation, the absorption band depth of gaseous CO2. Because the last three factors can be predicted to some extent, we can define a new parameter β that expresses specifically the strength of the gas–aerosols coupling while directly depending on the AOD. Combining estimations of β and top of the atmosphere radiance values extracted from the observed spectra within the CO2 gas band at 2μm, we evaluate the AOD and the surface reflectance by radiative transfer inversion. One should note that practically β can be estimated for a large variety of mineral or icy surfaces with the exception of CO2 ice when its 2μm solid band is not sufficiently saturated. Validation of the proposed method shows that it is reliable if two conditions are fulfilled: (i) the observation conditions provide large incidence or/and emergence angles (ii) the aerosols are vertically well mixed in the atmosphere. Experiments conducted on OMEGA nadir looking observations as well as CRISM multi-angular acquisitions with incidence angles higher than 65° in the first case and 33° in the second case produce very satisfactory results. Finally in a companion paper the method is applied to monitoring atmospheric dust spring activity at high southern latitudes on Mars using OMEGA.

A complete climatology of the aerosol vertical distribution on Mars from MEx/SPICAM UV solar occultations

We present the first results on solar occultations performed with the UV channel of SPICAM, on board Mars Express. From the dataset of over 900 occultations (performed between April 2004 and October 2011), about 640 atmospheric profiles of the martian atmosphere were derived. This dataset, spanning four martian years, allows characterization of the seasonal evolution and inter-annual comparisons of ozone and suspended particles. The dataset also includes observations of the Mars Year (MY) 28 global dust storm. In this paper the aforementioned data are analyzed with a focus on the aerosol profiles.We have mapped the seasonal behavior of the near-surface haze, revealing the typical behavior of the martian aerosol cycle, where the season most prone to develop dust storms (southern summer) shows aerosols lofted high in the atmosphere, whereas in the polar regions the aerosols are confined near the surface. More generally, aerosols seem to remain in the lower atmosphere at high latitudes and progressively penetrate to higher altitudes towards the tropics. This prevailing trend is probably related to enhanced atmospheric circulation at tropical regions due to high insolation and/or to higher cloud formation level in a warmer atmosphere.The dataset reveals frequent aerosol layers, found above or within the persistent near-surface haze. We have observed single and multiple layers (up to three layers in one profile) and we have mapped their properties. The highest layer altitudes observed during the global dust storm in the southern hemisphere, where thick layers form high above the abundant lower atmosphere dust haze.We present results on the analyzed Ångström coefficient α and its vertical variations. We also discuss the conversion of α into particle effective radius and present some examples of the effective radius vertical behavior.

The retrieval of altitude profiles of the Martian aerosol microphysical characteristics from the limb measurements of the Mars Express OMEGA spectrometer

Parameterization of the spectral dependence of the optical characteristics of Martian aerosols has been proposed for processing the results of measurements of outgoing radiation. A method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometry of the OMEGA instrument of the Mars Express mission have been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented. For the purpose of the interpretation of the data acquired from the optical remote sensing of planetary atmospheres, we consider how the spectral dependence of aerosol optical characteristics, in particular the volume coefficients of aerosol scattering and absorption and the phase function, can be parameterized in a specified, probably wide, spectral range. The method of such a parameterization has been proposed for the cases of a fixed chemical composition of the aerosol materials dominating in the atmosphere. It has been shown that these cases allow the required spectral dependences to be presented as a function of a small number of parameters, for which the parameters of the size distribution function of aerosol particles can be successfully used. However, since such direct calculations of the aerosol characteristics require an inadmissibly long period of time for the tasks of interpretation of the remote sensing data, an algorithm for organizing the parameterization function as a special, preliminary generated computer database has been suggested. This database provides the continuity in the dependence on the parameters, the specified computation accuracy, and the required output speed of the results. As a specific application, the parameterization of the spectral dependence of the optical characteristics of the Martian aerosols has been proposed for the tasks of processing the results of measurements of outgoing radiation. As a result, the method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometric measurements of the OMEGA instrument of the Mars Express mission has been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented.

The impact of Martian aerosols on the retrieval of temperature profiles from PFS measurements

Our purpose was a qualitative assessment of the impact of dust and water ice aerosols on the retrieved temperature profiles and the retrieval process itself in the Martian atmosphere. It aims to quantify the related uncertainties in the atmospheric temperature profiles derived from radiance measurements of the Planetary Fourier Spectrometer (PFS), currently operating on the Mars Express orbiter. In this study the effects of aerosol opacities on simulated data and retrieved temperature profiles were also investigated. From the analysis of the model atmosphere including dust and water ice with different size distributions it results that the dust component affects weighting functions and brightness temperatures less than water ice. A similar situation is also observed when different vertical distributions are considered. Unlike dust, water ice with different sizes of crystals evidently influences weighting functions and brightness temperatures. The impact of the considered water ice vertical distributions on brightness temperatures is noticeable only near 840 cm −1. Considering different dust opacities, the largest differences—5 K maximum—between retrieved temperature profiles were observed close to the surface, regardless assumptions on a size distribution or the refractive indices. Contrary to dust, the different sizes of water ice particles assumed during retrieval stronger affected the retrieved temperature profiles than water ice opacities. Moreover, the differences in the retrieved temperature profiles were amplified while wrong optical properties for dust as well as for water ice aerosol were assumed instead of the nominal case. This means that the wrong assumption can induce an additional source of the retrieval error and lead to unreasonable temperature profiles. In the cases of expected heavily loads water ice crystals, their size distribution in the Martian atmosphere should be known from other observations before the retrieval of the temperature profile is attempted. For the analyzed examples of real PFS measurements the impact of different dust vertical distributions on the retrieval of temperature profile is prominent only in layers close to the surface. However, these differences remain comparable with retrieval errors. All influences of dust on weighting functions, brightness temperatures and during retrieval can be neglected if the noise equivalent radiance (NER) of PFS is taken into account.

Scientific aspects of the optical depth sensor

The optical depth sensor (ODS) is designed for the monitoring of Martian dust opacity over a long period of time. Additionally, it could provide valuable information on aerosol size distribution and on cloud coverage at sunset and sunrise. The instrument was developed for the MARS96 Russian mission which unfortunately failed and the ATMIS meteorological package on the NETLANDER mission which unfortunately was cancelled. The instrument’s main attractive features for a meteorological mission to Mars are its low requirements of energy and data transfer resources. The paper describes the working principle and theoretical performance of ODS, simulated with a Martian aerosol and cloud model.

Optical properties of dust and the opacity of the Martian atmosphere

Particulate component of the Mars atmosphere composed by micron-sized products of soil weathering and water ice clouds strongly affects the current climate of the planet. In the absence of a dust storm so-called permanent dust haze with τ ≈ 0.2 in the atmosphere of Mars determines its thermal structure. Dust loading varies substantially with the season and geographic location, and only the data of mapping instruments are adequate to characterize it, such as TES/MGS and IRTM/Viking. In spite of vast domain of collected data, no model is now capable to explain all observed spectral features of dust aerosol. Several mineralogical and microphysical models of the atmospheric dust have been proposed but they cannot explain the pronounced systematic differences between the IR data ( τ = 0.05–0.2) and measurements from the surface (Viking landers, Pathfinder) which give the typical “clear” optical depth of τ ≈ 0.5 from one side, and ground-based observations in the UV–visible range showing much more transparent atmosphere, on the other side. Also the relationship between τ 9 and the visible optical depth is not well constrained experimentally so far. Future focused measurements are therefore necessary to study Martian aerosol.

Constraints on the size of Martian aerosols from Thermal Emission Spectrometer observations

We combine a robust multiple‐scattering radiative transfer algorithm with the Thermal Emission Spectrometer (TES) spectral data set in order to characterize the properties of Martian aerosol particles. Because of the importance of accurate model input when performing such retrievals, we include self‐consistent and physically plausible treatments of surface emissivity and atmospheric aerosol dielectric functions, as well as gaseous absorption effects. Considerable effort is expended in the identification and discussion of potential sources of error and uncertainty. Significant results stemming from this analysis are a new dust aerosol dielectric function that appears to well represent the IR spectral behavior sampled by TES for a wide range of dust loading conditions, two distinct populations of water ice particles with reff of ∼1–2 μm and ∼3–4 μm; and distinct departures in dust particle sizes during the 2001A global dust storm from the canonical 1.6–1.7 μm values. Very consistent aerosol size distributions are obtained when 9 μm dust and 12 μm ice optical depths retrieved from this analysis are compared to visible optical depths retrieved from TES solar band emission phase function sequences [Clancy et al., 2003]. Direct comparison of our optical depths to those available from the Planetary Data System (PDS) (as provided by the TES science team) reveals a systematic bias toward τ values which are 20–30% (or more) too small. Much of this offset stems from the fact that TES PDS aerosol optical depths are actually an approximation to τabsorption, which is ∼30% lower than τextinction for Mars dust aerosols. Additional biases in TES optical depths arise from assumptions of fixed surface emissivity and temperature.

Mars aerosol studies with the MGS TES emission phase function observations: Optical depths, particle sizes, and ice cloud types versus latitude and solar longitude

Emission phase function (EPF) observations taken in 1999–2001 by Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) support the broadest study of Martian aerosol properties to date. TES solar band and infrared (IR) spectral EPF sequences are analyzed to obtain first‐time seasonal/latitudinal distributions of visible optical depths, particle sizes, and single scattering phase functions. This combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45°S–45°N. Type 1 ice clouds exhibit small particle sizes (reff = 1–2 μm) and a distinctive backscattering increase. They are most prevalent in the southern hemisphere during aphelion, but also appear more widely distributed in season and latitude as topographic and high‐altitude (≥20 km) ice hazes. Type 2 ice clouds exhibit larger particle sizes (reff = 3–4 μm), a distinct side‐scattering minimum at 90–100° phase angles (characteristic of a change in particle shape relative to the type 1), and appear most prominently in the northern subtropical aphelion cloud belt. The majority of retrieved dust visible‐to‐IR optical depth ratios are indicative of reff = 1.5 ± 0.1 μm, consistent with Pathfinder and Viking/Mariner 9 reanalyses. However, increased ratios (2.7 versus 1.7) appear frequently in the northern hemisphere over LS = 50–200°, indicating substantially smaller dust particles sizes (reff = 1.0 ± 0.2 μm) at this time. In addition, larger (reff = 1.8–2.5 μm) dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm. Detailed spectral modeling of the TES visible band pass indicates agreement of EPF‐derived dust single scattering albedos (0.92–0.94) with the spectrally resolved results from Pathfinder observations.

Physical Properties of Dust in the Martian Atmosphere: Analysis of Contradictions and Possible Ways of Their Resolution

Atmospheric aerosols play an important role in forming the Martian climate. However, the basic physical properties of the Martian aerosols are still poorly known; there are many contradictions in their estimates. We present an analytical overview of the published results and potentialities of various methods. We consider mineral dust. Zonally averaged data obtained from mapping IR instruments (TES and IRTM) give the optical thickness of mineral aerosols τ9 = 0.05–0.1 in the 9-μm band for quite atmospheric conditions. There is a problem of comparing these estimates with those obtained in the visible spectral range. We suggest that the commonly used ratio τvis/τ9 >2 depends on the interpretation and it may actually be smaller. The ratio τvis/τ9 ≈ 1 is in better agreement with the IRIS data (materials like montmorillonite). If we assume that τvis/τ9 = 1 and take into account the nonspherical particle shape, then the interpretation of ground-based integrated polarimetric observations (τ < 0.04) can be reconciled with IR measurements from the orbit. However, for thin layers, the sensitivity of both methods to the optical thickness is poorly understood: on the one hand, polarimetry depends on the cloud cover and, on the other hand, the interpretation of IR measurements requires that the atmospheric temperature profile and the surface temperature and emissivity be precisely known. For quite atmospheric conditions, the local optical-thickness estimates obtained by the Bouguer–Lambert–Beer method and from the sky brightness measured from Viking 1 and 2 and Mars Pathfinder landers are much larger: τ = 0.3–0.6. Estimates of the contrasts in images from theVikingorbiters yield the same values. Thus, there is still a factor of 3 to 10 difference between different groups of optical-thickness estimates for the quiet atmosphere. This difference is probably explained by the contribution of condensation clouds and/or by local/time variations.

Simulation of the Martian dust aerosol at low wind speeds

Performing realistic simulations is crucial for developing, testing, and subsequently analyzing results of experiments sent to the surface of Mars. A wind tunnel has been constructed, in which the atmospheric conditions of pressure and wind speed are controlled to match those observed by the Pathfinder mission to Mars. Injection into the wind tunnel of an analogue dust from Salten Skov in Denmark allows simulation of the Martian aerosol. Here experiments can be tested in preparation for a planned mission to the planet (Mars Exploration Rovers to be launched in 2003). Observations of adhesion and cohesion effects have been made in the wind tunnel, which are relevant to particle transport and of significance for validating the performance of specific experiments on Mars. Preliminary studies have been made, at Mars atmospheric pressure, of dust capture on magnet arrays similar to those flown on the Mars Pathfinder mission.

The complex refractive index of limestone particles: an extension to the FIR range for Mars applications

Theoretical studies and numerical models of the atmosphere and surface of Mars need the knowledge of the optical constants of candidate materials for Martian dust, in a wavelength range as wide as possible. Limestone, as a carbonate-bearing material, is commonly considered a likely component particularly important for its links with the climate evolution and water resources on Mars. In a previous paper, we reported the complex indices of refraction of submicron particles of limestone, derived from laboratory transmission spectra in the wavelength range 3.5– 20 μm by means of the dispersion theory. In this work we present the same quantities in a wider spectral range extending from 1.5 up to 62.5 μm . Such an extension is particularly important since limestone, as well as other carbonates, has some of its characteristic features between 20 and 50 μm . Our data are discussed and compared with those given by other authors and obtained with a different method (i.e. reflection measurements) on samples consisting of pressed pellets of randomly oriented calcite grains. As in the case of the previous work, our results point out, again, that the extinction spectra of submicron particles can be better reproduced using optical constants directly obtained in the laboratory for particulate materials. Finally, the extinction and emission properties of limestone grains are used in order to tentatively identify carbonates on Mars and to understand whether these materials are present in the Martian aerosol or on the surface. Our results seem to suggest that, limestone particles can be a minor component of the atmospheric dust rather than of the surface regolith, provided that some bands observed in the Martian spectra will be finally ascribed to such material.

Capture of magnetic dust in a simulated Martian aerosol: the importance of aerodynamics

The magnetic properties of dust in the Martian atmosphere have been studied on the Pathfinder mission by observing capture on permanent magnets. The present simulations are the first to be performed at pressures and wind speeds typical on Mars. Hematite is around a factor of ten less magnetic than current estimates for the Martian atmospheric dust, yet at low simulated wind speeds ( <1 m/ s ) this mineral captures even on the weaker of the Pathfinder magnets, as does the dust on Mars. This emphasises the critical dependency on aerodynamics and suggests that the suspended Martian dust may be similarly weakly magnetic.

Remote sounding of the Martian dust from ISO spectroscopy in the [formula omitted] bands

This paper presents a study of Martian aerosols based on the spectral observations near 2.7 μm . Simulations by Titov et al. [Planet. Space Sci. 48 (2000) 67] showed that the depth and the shape of saturated 2.7 μm band of atmospheric CO 2 are sensitive to the presence of aerosols. This allows one to determine the aerosol optical depth, the scale height, and optical properties from the spectral measurements in the band. For the first time this method is applied to two disk-averaged spectra of Mars recorded by the Infrared Space Observatory (ISO). The analysis implies existence of sharp absorption band in the dust spectrum between 2.7 and 2.8 μm that probably indicates the presence of phyllosilicates (for instance, montmorillonite) in the dust. The best fit to the ISO spectra is obtained in the model with column optical depth of 0.33±0.13. This value is in good agreement with simultaneous Mars Pathfinder and Hubble Space Telescope observations.

A new method of remote sounding of the Martian aerosols by means of spectroscopy in the 2.7 μm CO 2 band

We present a new method of sounding of aerosols in the atmosphere of Mars. It is based on the remote spectroscopic measurements of the solar radiation reflected by the planet in the region of the 2.7 μm absorption band of atmospheric CO 2. The band is so strong that the radiance in its center is equal to 0 for the dust-free Martian atmosphere. The presence of suspended dust results in that some fraction of solar photons is scattered back to space without reaching the surface. Thus the intensity measured in the bottom of the band differs from 0 and can be used to determine the aerosol optical depth and to estimate its vertical distribution. We formulate general requirements for the spectroscopic observations that can provide optimal sounding of the atmospheric dust on Mars. The aerosol sounding capabilities of the Planetary Fourier Spectrometer experiment for the Mars Express mission are discussed in more detail. The equations for the radiation reflected by the non-homogeneous atmosphere derived in this work in a single scattering approximation can find applications beyond the scope of the paper.