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1.
Data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and the Mars Odyssey Thermal Emission Imaging System (THEMIS) instruments are used to assess the mineralogic and dust cover characteristics of landing regions proposed for the Mars Science Laboratory (MSL) mission. Candidate regions examined in this study are Eberswalde crater, Gale crater, Holden crater, Mawrth Vallis, Miyamoto crater, Nili Fossae Trough, and south Meridiani Planum. Compositional units identified in each region from TES and THEMIS data are distinguished by variations in hematite, olivine, pyroxene and high-silica phase abundance, whereas no units are distinguished by elevated phyllosilicate or sulfate abundance. Though phyllosilicate minerals have been identified in all sites using near-infrared observations, these minerals are not unambiguously detected using either TES spectral index or deconvolution analysis methods. For some of the sites, small phyllosilicate outcrop sizes relative to the TES field of view likely hinder phyllosilicate mineral detection. Porous texture and/or small particle size (<∼60 μm) associated with the phyllosilicate-bearing surfaces may also contribute to non-detections in the thermal infrared data sets, in some areas. However, in Mawrth Vallis and Nili Fossae, low phyllosilicate abundance (<10-20 areal %, depending on the phyllosilicate composition) is the most likely explanation for non-detection. TES data over Mawrth Vallis indicate that phyllosilicate-bearing surfaces also contain significant concentrations (>15%, possibly up to ∼40%) of a high-silica phase such as amorphous silica or zeolite. High-silica phase abundance over phyllosilicate-bearing surfaces in Mawrth Vallis is higher than that of surrounding surfaces by 10-15%. With the exception of these high-silica surfaces in Mawrth Vallis, regions examined in this study exhibit similar bulk mineralogical compositions to that of most low-albedo regions on Mars; the MSL scientific payload will thus be able to provide important information on surface materials typical of low-albedo regions in addition to investigating the origin of phyllosilicate and/or sulfate deposits. With the exception of Gale crater, all of the landing sites have relatively low dust cover compared to classic high-albedo regions (Tharsis, Arabia and Elysium) and to previous landing sites in Gusev Crater, Utopia Planitia, and Chryse Planitia. 相似文献
2.
Michael D. Smith 《Icarus》2009,202(2):444-452
We use infrared images obtained by the Thermal Emission Imaging System (THEMIS) instrument on-board Mars Odyssey to retrieve the optical depth of dust and water ice aerosols over more than 3.5 martian years between February 2002 (MY 25, Ls=330°) and December 2008 (MY 29, Ls=183°). These data provide an important bridge between earlier TES observations and recent observations from Mars Express and Mars Reconnaissance Orbiter. An improvement to our earlier retrieval [Smith, M.D., Bandfield, J.L., Christensen, P.R., Richardson, M.I., 2003. J. Geophys. Res. 108, doi:10.1029/2003JE002114] to include atmospheric temperature information from THEMIS Band 10 observations leads to much improved retrievals during the largest dust storms. The new retrievals show moderate dust storm activity during Mars Years 26 and 27, although details of the strength and timing of dust storms is different from year to year. A planet-encircling dust storm event was observed during Mars Year 28 near Southern Hemisphere Summer solstice. A belt of low-latitude water ice clouds was observed during the aphelion season during each year, Mars Years 26 through 29. The optical depth of water ice clouds is somewhat higher in the THEMIS retrievals at ∼5:00 PM local time than in the TES retrievals at ∼2:00 PM, suggestive of possible local time variation of clouds. 相似文献
3.
The detection of gray crystalline hematite deposits on Mars by Thermal Emission Spectrometer (TES) has been used to argue for the presence of liquid water on Mars in the distant past. By methanol-thermal treatment of anhydrous FeCl3 at low temperatures (70-160 °C), crystalline gray hematite with layered structure was synthesized, based on this result an alternative explanation for the origin of martian hematite deposits is suggested. Methane could be abundant in the early martian atmosphere; process such as photochemical oxidation of methane could result in the formation of ocean or pool of organic compounds such as methanol, which provides an environment for the formation of large-scale hematite deposits on Mars. 相似文献
4.
The Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument has returned over 200 million thermal infrared spectra of Mars taken between March 1999 and August 2004. This represents one of the most complete records of spatial and temporal changes of the martian atmosphere ever recorded by an orbiting spacecraft. Previous reports of the standard TES retrieval of aerosol optical depth have been limited to those observations taken over surfaces with temperatures above 210 K, limiting the spatiotemporal coverage of Polar Regions with TES. Here, we present an extension to the standard TES retrieval that better models the effects of cold surfaces below 200 K. This modification allows aerosol optical depth to be retrieved from TES spectra over a greater spatiotemporal range than was previously possible, specifically in Polar Regions. This new algorithm is applied to the Polar Regions to show the seasonal variability in dust and ice optical depth for the complete temporal range of the TES database (Mars Year 24, Ls=104°, 1 March 1999 to Mars Year 24, Ls=82°, 31 August 2004). 相似文献
5.
We examine the nature of the surface layer in Gale Crater as determined from high-resolution thermal and visible Mars Odyssey Thermal Emission Imaging System (THEMIS) data as well as how our conclusions compare to past analyses. At THEMIS resolution, the thermal surface structure is dominated by local control, thus providing us with detailed images that contain thermophysical information as well. Using these data sets we have created a map of the area, defining units based primarily on their geomorphology as determined from the daytime thermal and visible images and then using the nighttime thermal data to interpret the nature of the surface layer within each unit. Seven units have been defined: (i) partially blanketed knobby plateaus, (ii) crater walls with terrain similar to that on the plateaus on the upper half and exposed, rocky surfaces on the lower half, (iii)-(v) three floor units with varying combinations of bedrock and indurated and/or particulate deposits, (vi) sand sheets, and (vii) a central mound, consisting of indurated and/or rocky material forming layers, terraces, and slides, covered by particulate material that tapers in thickness downslope. Additionally, dozens of channels have been observed on the crater walls and central mound. The results indicate that aeolian processes have played a major role in shaping much of the present surface layer within Gale and may still be active today. Because of the dramatic size and structure of Gale, the winds are most likely controlled by the local topography. Additionally, the presence and frequency of channels within Gale bolster hypotheses involving aqueous episodes in the history of the crater. 相似文献
6.
We present the seasonal and geographical variations of the martian water vapor monitored from the Planetary Fourier Spectrometer Long Wavelength Channel aboard the Mars Express spacecraft. Our dataset covers one martian year (end of Mars Year 26, Mars Year 27), but the seasonal coverage is far from complete. The seasonal and latitudinal behavior of the water vapor is globally consistent with previous datasets, Viking Orbiter Mars Atmospheric Water Detectors (MAWD) and Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES), and with simultaneous results obtained from other Mars Express instruments, OMEGA and SPICAM. However, our absolute water columns are lower and higher by a factor of 1.5 than the values obtained by TES and SPICAM, respectively. In particular, we retrieve a Northern midsummer maximum of 60 pr-μm, lower than the 100-pr-μm observed by TES. The geographical distribution of water exhibits two local maxima at low latitudes, located over Tharsis and Arabia. Global Climate Model (GCM) simulations suggest that these local enhancements are controlled by atmospheric dynamics. During Northern spring, we observe a bulge of water vapor over the seasonal polar cap edge, consistent with the northward transport of water from the retreating seasonal cap to the permanent polar cap. In terms of vertical distribution, we find that the water volume mixing ratio over the large volcanos remains constant with the surface altitude within a factor of two. However, on the whole dataset we find that the water column, normalized to a fixed pressure, is anti-correlated with the surface pressure, indicating a vertical distribution intermediate between control by atmospheric saturation and confinement to a surface layer. This anti-correlation is not reproduced by GCM simulations of the water cycle, which do not include exchange between atmospheric and subsurface water. This situation suggests a possible role for regolith-atmosphere exchange in the martian water cycle. 相似文献
7.
The Thermal Emission Spectrometer (TES) has observed a high-silica material in the dark regions of Mars that is spectrally similar to obsidian glass and may have a volcanic origin. An alternate interpretation is that the spectrally amorphous material consists of clay minerals or some other secondary material, formed by chemical alteration of surface rocks. The regions where this material is observed (e.g., Acidalia Planitia) have relatively high spectral contrast, suggesting that the high-silica material exists as coarse particulates, indurated soils or cements, within rocks, or as indurated coatings on rock surfaces. The geologic interpretation of this spectral result has major implications for understanding magmatic evolution and weathering processes on Mars. One of the complications in interpreting spectral observations of glasses and clay minerals is that both are structurally and compositionally complex. In this study, we perform a detailed spectroscopic analysis of indurated smectite clay minerals and relate their thermal emission spectral features to structural and crystal chemical properties. We examine the spectral similarities and differences between smectite clay minerals and obsidian glass from a structural-chemical perspective, and make further mineralogical interpretations from previous TES results. The results suggest that neither smectite clays nor any clay mineral with similar structural and chemical properties can adequately explain TES observations of high-silica materials in some martian dark regions. If the spectrally amorphous materials observed by TES do represent an alteration product, then these materials are likely to be poorly crystalline aluminosilicates. While all clay minerals have Si/O ratios ?0.4, the position of the emissivity minimum at Mars suggests a Si/O ratio of 0.4-0.5. The spectral observation could be explained by the existence of a silica-rich alteration product, such as Al- or Fe-bearing opal, an intimate physical mixture of relatively pure silica and other aluminosilicates (such as clay minerals or clay precursors), or certain zeolites. The chemical alteration of basaltic rocks on Mars to phyllosilicate-poor, silica-rich alteration products provides a geologically reasonable and consistent explanation for the global TES surface mineralogical results. 相似文献
8.
The Thermal Emission Spectrometer (TES) on the Mars Global Surveyor spacecraft has detected deposits of coarse-grained, gray crystalline hematite in Sinus Meridiani, Aram Chaos, and Vallis Marineris. We argue that the key to the origin of gray hematite is that it requires crystallization at temperatures in excess of about 100 °C. We discuss thermal crystallization (1) as diagenesis at a depth of a few kilometers of sediments originally formed in low-temperature waters, or (2) as precipitation from hydrothermal solution. In Aram Chaos, a combination of TES data, Mars Orbiter Camera images, and Mars Orbiter Laser Altimeter (MOLA) topography suggests that high concentrations of hematite were formed in planar strata and have since been exposed by erosion of an overlying light-toned, caprock. Lesser concentrations of hematite are found adjacent to these strata at lower elevations, which we interpret as perhaps due to accumulation from physical weathering. The topography and the collapsed nature of the chaotic terrain favor a hydrothermally charged aquifer as the original setting where the hematite formed. Concentration of iron into such an ore-like body would be chemically favored by saline, Cl-rich hydrothermal fluids. An alternative sedimentary origin requires post-depositional burial to a depth of ∼3-5 km to induce thermally driven recrystallization of fine-grained iron oxides to coarse-grained hematite. This depth of burial and re-exposure is difficult to reconcile with commonly inferred martian geological processes. However, shallow burial accompanied by post-burial hydrothermal activity remains plausible. When the hematite regions originally formed, redox balance requires that much hydrogen must have been evolved to complement the extensive oxidation. Finally, we suggest that the coexistence of several factors required to form the gray hematite deposits would have produced a favorable environment for primitive life on early Mars, if it ever existed. These factors include liquid water, abundant electron donors in the form of H2, and abundant electron acceptors in the form of Fe3+. 相似文献
9.
We present an application of a multivariate analyses technique on data returned by the Planetary Fourier Spectrometer (PFS) instrument on board the ESA’s Mars Express (MEX) spacecraft in order to separate the atmospheric contribution from the observed radiation. We observe that Thermal/Far Infrared spectra returned from Mars, covering almost a whole martian year, can be represented by a linear model using a limited set of end-member spectra. We identify the end-members as the suspended mineral dust and water ice clouds, but no surface signature was found. We improve previous studies performed with data from the Thermal Emission Spectrometer (TES) thanks to the higher spectral resolution of PFS. This allows for distinguishing narrow gaseous bands present in the martian atmosphere. Furthermore, the comparison of results from PFS and TES with data collected in 1971 by the Mariner 9 Infrared Interferometer Spectrometer (IRIS) shows an atmospheric dust component with similar spectral behavior. This might indicate homogeneity of the dust source regions over a time period of more than 30 years. 相似文献
10.
The global martian volcanic evolutionary history 总被引：1，自引：0，他引：1
Stephanie C. Werner 《Icarus》2009,201(1):44-68
Viking mission image data revealed the total spatial extent of preserved volcanic surface on Mars. One of the dominating surface expressions is Olympus Mons and the surrounding volcanic province Tharsis. Earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the Viking orbiter camera. Here, a global investigation based on high-resolution image data gathered by the High-Resolution Stereo Camera (HRSC) during the first years of Mars Express orbiting around Mars is presented. Additionally, Mars Orbiter Camera (MOC) and Thermal Emission Imaging System (THEMIS) images were used for more detailed and complementary information. The results reveal global volcanism during the Noachian period (>3.7 Ga) followed by more focused vent volcanism in three (Tharsis, Elysium, and Circum-Hellas) and later two (Tharsis and Elysium) volcanic provinces. Finally, the volcanic activity became localized to the Tharsis region (about 1.6 Ga ago), where volcanism was active until very recently (200-100 Ma). These age results were expected from radiometric dating of martian meteorites but now verified for extended geological units, mainly found in the Tharsis Montes surroundings, showing prolonged volcanism for more than 3.5 billions years. The volcanic activity on Mars appears episodic, but decaying in intensity and localizing in space. The spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of Mars. 相似文献
11.
Ai Inada Mark I. Richardson Timothy H. McConnochie Melissa J. Strausberg Huiqun Wang James F. Bell III 《Icarus》2007,192(2):378-395
High-resolution observations of atmospheric phenomena by the Mars Odyssey Thermal Emission Imaging System (THEMIS) during its first mapping year are presented. An atmospheric campaign was implemented on the basis of previous spacecraft imaging. This campaign, however, proved of limited success. This appears to be due to the late local time of the Odyssey orbit (the locations of activity at 4–6 p.m. appear to be different from those at 2 p.m.). Ironically, images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features. While many previously recognized features were found, novel THEMIS observations included persistent clouds in the southern polar layered deposits, dust or condensate plumes on the northern polar layered deposits, dust plumes as constituent parts of local dust storms, and mesospheric clouds. The former two features tend to be aligned parallel and normal to polar troughs, respectively, suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits. This is consistent with katabatic drainage of air off the polar deposits, analogous to flow off Antarctica. The observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses (as opposed to dust devils) in initiation of dust storms, but is also seen to be morphologically identical to dust lifting in terrestrial dust storms. As Odyssey moves to earlier local times, we suggest that the atmospheric campaign from the first mapping year be repeated. 相似文献
12.
We conducted a systematic, global survey using Thermal Emission Imaging System Infrared (THEMIS IR) coverage (∼100 m/pixel) to search for large alluvial fans in impact craters on Mars. Our survey has focused on large fans (apron areas greater than ∼40 km2, usually located in craters greater than 20 km in diameter) due to the resolution of the THEMIS images and Mars Orbiter Laser Altimeter (MOLA) coverage. We find that the host craters are found to have a distinctive diameter range from 30-150 km. The fans generally cluster in three geographic areas—southern Margaritifer Terra, southwestern Terra Sabaea, and southwestern Tyrrhena Terra, however several outliers do exist. The alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography. Fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter. Smaller fan aprons in general have higher, more variable concavity. The source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters. 相似文献
13.
Joshua L. Bandfield 《Icarus》2009,202(2):414-8420
Slopes are present in martian apparent surface emissivity observations collected by the Thermal Emission Spectrometer (TES) and the Thermal Emission Imaging System (THEMIS). These slopes are attributed to misrepresenting the surface temperature, either through incorrect assumptions about the maximum emissivity of surface materials or the presumption of a uniform surface temperature within the field of view. These incorrect assumptions leave distinct characteristics in the resulting apparent emissivity data that can be used to gain a better understanding of the surface properties. Surfaces with steep slopes typically have a variable surface temperatures within the field of view that cause distinct and highly variable slopes in apparent emissivity spectra based on the observing conditions. These properties are documented on the southwestern flank of Apollinaris Patera and can be reasonably approximated by modeled data. This spectral behavior is associated with extremely rough martian surfaces and includes surfaces south of Arsia Mons and near Warrego Valles that also appear to have high slopes in high resolution images. Surfaces with low maximum values of emissivity have apparent emissivity spectra with more consistent spectral slopes that do not vary greatly based on observing conditions. This spectral surface type is documented in Terra Serenum and is consistent with associated high resolution images that do not indicate the presence of a surface significantly rougher that the surrounding terrain. 相似文献
14.
The interval from Ls = 330° in Mars Year (MY) 26 until Ls = 84° in MY 27 has been used to compare and validate measurements from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and the Mars Express Planetary Fourier Spectrometer (PFS). We studied differences between atmospheric temperatures observed by the two instruments. The best agreement between atmospheric temperatures was found at 50 Pa between 40°S and 40°N latitude, where differences were within ±5 K. For other atmospheric levels, differences as large as ∼25 K were observed between the two instruments at some locations. The largest temperature differences occurred mainly over the Hellas Planitia, Argyre Planitia, Tharsis and Valles Marineris regions.On this basis we report on the variability of the martian atmosphere during the 5.5 martian years of Mars climatology obtained by combining the two data sets from TES and PFS. Atmospheric temperatures at 50 Pa responded to the global-scale dust storms of MY 25 and in MY 28 raising temperatures from ∼220 K to ∼250 K during the daytime. An atmospheric temperature of ∼140 K at 50 Pa was observed poleward of 70°N during northern winter and poleward of 60°S during southern winter each year in both the PFS and TES results. Water vapor observed by the two spectrometers showed consistent seasonal and latitudinal variations. 相似文献
15.
The extensive impact cratering record on Mars combined with evidence from SNC meteorites suggests that a significant fraction of the surface is composed of materials subjected to variable shock pressures. Pressure-induced structural changes in minerals during high-pressure shock events alter their thermal infrared spectral emission features, particularly for feldspars, in a predictable fashion. To understand the degree to which the distribution and magnitude of shock effects influence martian surface mineralogy, we used standard spectral mineral libraries supplemented by laboratory spectra of experimentally shocked bytownite feldspar [Johnson, J.R., Hörz, F., Christensen, P., Lucey, P.G., 2002b. J. Geophys. Res. 107 (E10), doi:10.1029/2001JE001517] to deconvolve Thermal Emission Spectrometer (TES) data from six relatively large (>50 km) impact craters on Mars. We used both TES orbital data and TES mosaics (emission phase function sequences) to study local and regional areas near the craters, and compared the differences between models using single TES detector data and 3×2 detector-averaged data. Inclusion of shocked feldspar spectra in the deconvolution models consistently improved the rms errors compared to models in which the spectra were not used, and resulted in modeled shocked feldspar abundances of >15% in some regions. However, the magnitudes of model rms error improvements were within the noise equivalent rms errors for the TES instrument [Hamilton V., personal communication]. This suggests that while shocked feldspars may be a component of the regions studied, their presence cannot be conclusively demonstrated in the TES data analyzed here. If the distributions of shocked feldspars suggested by the models are real, the lack of spatial correlation to crater materials may reflect extensive aeolian mixing of martian regolith materials composed of variably shocked impact ejecta from both local and distant sources. 相似文献
16.
Thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters. Consequently, surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season. To investigate these temporal variations, we processed three Mars years of Mars Global Surveyor Thermal Emission Spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia. These maps show broad regions with diurnal and seasonal differences up to 200 J m−2 K−1s−1/2 at mid-latitudes (60° S to 60° N) and 600 J m−2 K−1s−1/2 or greater in the polar regions. We compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5° resolution, delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials. The thermal behavior of most regions on Mars appears to be dominated by layering, with upper layers of higher thermal inertia (e.g., duricrusts or desert pavements over fines) prevailing in mid-latitudes and upper layers of lower thermal inertia (e.g., dust-covered rock, soils with an ice table at shallow depths) prevailing in polar regions. Less common are regions dominated by horizontal mixtures, such as those containing differing proportions of rocks, sand, dust, and duricrust or surfaces with divergent local slopes. Other regions show thermal behavior that is more complex and not well-represented by two-component surface models. These results have important implications for Mars surface geology, climate modeling, landing-site selection, and other endeavors that employ thermal inertia as a tool for characterizing surface properties. 相似文献
17.
Surficial Geologic Surveys of Gale Crater and Melas Chasma, Mars: Integration of Remote-Sensing Data
Remote-sensing observations of Gale Crater and Melas Chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions. Data sets analyzed include geologic maps, Mars Orbiter Laser Altimeter (MOLA) elevation, Thermal Emission Spectrometer (TES) albedo, TES thermal inertia, MOLA residual pulse width, TES rock abundance, and Viking and Mars Orbiter Camera images. Using these data sets, we constrain the properties of and processes acting on the present surface and create self-consistent models for the surface layer. Surface properties within Gale Crater are variable and complex, and interpreting the surface layer is not straightforward. Observations indicate that aeolian processes have shaped some of the intracrater surface, but other areas do not comply with this model and have counterintuitive surface characteristics. In contrast, aeolian activity appears to have played a large role in shaping the present-day physical structure of all surfaces in Melas Chasma and is reflected in the remote-sensing data sets. Here we summarize our analysis and discuss the surface attributes as determined from these data sets. 相似文献
18.
Validation of martian meteorological data assimilation for MGS/TES using radio occultation measurements 总被引：1，自引：0，他引：1
We describe an assimilation of thermal profiles below about 40 km altitude and total dust opacities into a general circulation model (GCM) of the martian atmosphere. The data were provided by the Thermal Emission Spectrometer (TES) on board the Mars Global Surveyor (MGS) spacecraft. The results of the assimilation are verified against an independent source of contemporaneous data represented by radio occultation measurements with an ultra-stable radio oscillator, also aboard MGS. This paper describes a comparison between temperature profiles retrieved by the radio occultation experiments and the corresponding profiles given by both an independent, carefully tuned GCM simulation and by an assimilation of TES observations performed over the period of time from middle, northern summer in martian year 24, corresponding to May 1999, until late, northern spring in martian year 27, corresponding to August 2004. This study shows that the assimilation of TES measurements improves the overall agreement between radio occultation observations and the GCM analysis, in particular below 20 km altitude, where the radio occultation measurements are known to be most accurate. Discrepancies still remain, mostly during the global dust storm of year 2001 and at latitudes around 60° N in northern winter-early spring. These are the periods of time and locations, however, for which discrepancies between TES and radio occultation profiles are also shown to be the largest. Finally, a further direct validation is performed, comparing stationary waves at selected latitudes and time of year. Apart from biases at high latitudes in winter time, data assimilation is able to represent the correct wave behaviour, which is one major objective for martian assimilation. 相似文献
19.
We present a Mars General Circulation Model (GCM) numerical investigation of the physical processes (i.e., wind stress and dust devil dust lifting and atmospheric transport) responsible for temporal and spatial variability of suspended dust particle sizes. Measurements of spatial and temporal variations in airborne dust particles sizes in the martian atmosphere have been derived from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) spectral and emission phase function data [Wolff, M.J., Clancy, R.T., 2003. J. Geophys. Res. (Planets) 108 (E9), doi:10.1029/2003JE002057. 1-1; Clancy, R.T., Wolff, M.J., Christensen, P.R., 2003. J. Geophys. Res. (Planets) 108 (E9), doi:10.1029/2003JE002058. 2-1]. The range of dust particle sizes simulated by the NASA Ames GCM is qualitatively consistent with TES-derived observations of effective dust particle size variability. Model results suggest that the wind stress dust lifting scheme (which produces regionally confined dust lifting) is the process responsible for the majority of the dust particle size variability in the martian atmosphere. Additionally, model results suggest that atmospheric transport processes play an important role in the evolution of atmospheric dust particles sizes during substantial dust storms on Mars. Finally, we show that including the radiative effects of a spatially variable particle size distribution significantly influences thermal and dynamical fields during the dissipation phase of the simulated global dust storm. 相似文献
20.
Directional thermal infrared measurements of the martian surface is one of a variety of methods that may be used to characterize surface roughness and slopes at scales smaller than can be obtained by orbital imagery. Thermal Emission Spectrometer (TES) emission phase function (EPF) observations show distinct apparent temperature variations with azimuth and emission angle that are consistent with the presence of warm, sunlit and cool, shaded slopes at typically ∼0.1 m scales. A surface model of a Gaussian distribution of azimuth independent slopes (described by θ-bar) is combined with a thermal model to predict surface temperature from each viewing angle and azimuth of the TES EPF observation. The models can be used to predict surface slopes using the difference in measured apparent temperature from 2 separate 60-70° emission angle observations taken ∼180° in azimuth relative to each other. Most martian surfaces are consistent with low to moderate slope distributions. The slope distributions display distinct correlations with latitude, longitude, and albedo. Exceptionally smooth surfaces are located at lower latitudes in both the southern highlands as well as in high albedo dusty terrains. High slopes are associated with southern high-latitude patterned ground and north polar sand dunes. There is little apparent correlation between high resolution imagery and the derived θ-bar, with exceptions such as duneforms. This method can be used to characterize potential landing sites by assuming fractal scaling behavior to meter scales. More precisely targeted thermal infrared observations from other spacecraft instruments are capable of significantly reducing uncertainty as well as reducing measurement spot size from 10s of kilometers to sub-kilometer scales. 相似文献