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The difference in brightness between shadowed and sunlit regions in space images of Mars is a measure of the optical depth of the atmosphere. The translation of this difference into optical depth is what we name the “shadow method”. Our analysis of two HRSC data-sets and a HiRISE data-set indicates that it is possible to estimate the optical depth with the shadow method. In colors between yellow and red the accuracy may be around ±15%, and in some cases ±8-10%. In other colors we found larger errors.We came to these results in two steps. First, we investigated in how far shadow method retrievals are proportional to the true optical depth. To this end we analyzed about 150 locations in Valles Marineris that were imaged by HRSC. Whereas the studied region spans about 8 km in altitude we were able to study the relation between altitude and shadow-method retrievals. Retrievals from five HRSC panchromatic (675 ± 90 nm) stereo images yielded scale-heights with an average of 12.2 ± 0.7 km, which is very close to the expected local pressure scale height. Many studies have shown that the scale-height of optical depth and pressure commonly are similar. This indicates that the shadow method retrievals are on average close to proportional to the optical depth, because otherwise these would probably not yield a correct scale-height. HRSC’s red image yielded very similar results, but the blue, green, and NIR images did not.Next, we compared optical depth measurements by the two MER rovers with shadow method retrievals from orbiter images of the rover exploration sites. Retrievals with the shadow method appear systematically smaller than the rover measurements; dividing the retrievals by a “correction factor” yields an estimate of the real optical depth. Retrievals from three HRSC panchromatic stereo images of a region near the Spirit rover yielded a correction factor of 0.63 ± 0.09 when the sunlit comparison regions were at varying and more or less arbitrary distances from the shadows and 0.71 ± 0.06 when these were close together. Twenty retrievals from a HiRISE red (650 ± 100 nm) image of the Opportunity exploration site similarly yielded 0.68 ± 0.09. The results from these two case studies suggest that the shadow method has an accuracy of about ±15% or around ±8-10% in the best cases. 相似文献
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E.V. Petrova N.M. Hoekzema W.J. Markiewicz N. Thomas O.J. Stenzel 《Planetary and Space Science》2012,60(1):287-296
In this paper we describe and evaluate the so-called shadow method. This method can be used to estimate the optical depth of the Martian atmosphere from the differences in brightness between shadowed and sunlit regions observed from an orbiter. We present elaborate and simplified versions of the method and analyze the capabilities and the sources of errors. It proves essential to choose shadowed and sunlit comparison regions with similar surface properties. Accurate knowledge of the observing geometry, including the slopes of the observed region, is important as well, since the procedure should be corrected for the non-horizontal surface. Moreover, the elaborate version of the shadow method can be sensitive to (i) the optical model of aerosols and (ii) the assumed bi-directional reflectance function of the surface. To obtain reliable estimates, the analyzed images must have a high spatial resolution, which the HiRISE camera onboard the MRO provides. We tested the shadow method on two HiRISE images of Victoria crater (TRA_0873_1780 and PSP_001414_1780) that were taken while this crater was the exploration site of the Opportunity rover. While the rover measured optical depth τ approximately in the ranges from 0.43 to 0.53 and from 0.53 to 0.59 by imaging the sun, our shadow procedure yielded τ about 0.50 and 0.575, respectively (from the HiRISE's red images). Thus, the agreement is quite good. The obtained estimates of the surface albedo are about 0.20 and 0.17, respectively. 相似文献
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John A. Paquette Cecile Engrand Oliver Stenzel Martin Hilchenbach Jochen Kissel the COSIMA Team 《Meteoritics & planetary science》2016,51(7):1340-1352
The calcium‐aluminum‐rich inclusions (CAIs) found in chondritic meteorites are probably the oldest solar system solids, dating back to 4567.30 ± 0.16 million years ago. They are thought to have formed in the protosolar nebula within a few astronomical units of the Sun, and at a temperature of around 1300 K. The Stardust mission found evidence of CAI‐like material in samples recovered from comet Wild 2. The appearance of CAIs in comets, which are thought to be formed at lower temperatures and larger distances from the Sun, is only explicable if some mechanism allows the efficient transfer of such objects from the inner solar nebula to the outer solar nebula. Such mechanisms have been proposed such as an X‐wind or turbulence. In this work, particles collected from within the coma of comet 67P/Churyumov–Gerasimenko are examined for compositional evidence of the presence of CAIs. COSIMA (the Cometary Secondary Ion Mass Analyzer) uses secondary ion mass spectrometry to analyze the composition of cometary dust captured on metal targets. While CAIs can have a radius of centimeters, they are more typically a few hundred microns in size, and can be smaller than 1 μm, so it is conceivable that particles visible on COSIMA targets (ranging in size from about 10 μm to hundreds of microns) could contain CAIs. Using a peak fitting technique, the composition of a set of 13 particles was studied, looking for material rich in both calcium and aluminum. One such particle was found. 相似文献
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Studies of heavy metal concentrations in porewaters and in sediments from the Weser Estuary, Germany, indicate that the depth distribution of Mn, Cd, and Cu in the solid phase is predominantly influenced by the subsurface redox regime, while Ni shows only moderate alteration. Based on solid-phase heavy metal data from eight locations in the study area, linear regressions of Fe, Mn, Cu, Ni, and Cd on Al allowed differences between the initial metal concentration and the concentration preserved in the sediments to be predicted. We calculate that, due to early diagenetic processes, Mn is enriched to 145 percent, while Cu and Cd are depleted to 71 percent and 46 percent, respectively, of the initial metal concentration in the near-surface sediment. Maximum depletion of Cd (84 percent), Cu (68 percent), Mn (54 percent), and Ni (24 percent) concentrations in the sediment, observed at a restricted area downcore, indicate the importance of post-depositional processes to metal preservation in the sediment. Without knowledge of the quantitative effects of diagenetic reactions on the preservation of metal concentrations in sediments, the depth distribution of metals in sediment cores may be misinterpreted as the effect of human activities. 相似文献
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Dr. H. B. Stenzel 《International Journal of Earth Sciences》1965,54(2):619-631
Zusammenfassung An der Typ-Lokalität des Littig phosphorite-cobble paraconglomerate an der Basis der Midway group (Dan-Stufe) wurden drei Brachiopoden-Arten aufgefunden. Eine dieser drei Arten, ein hornschaliger inartikulater Brachiopode, hat wahrscheinlich dasselbe Alter wie das Konglomerat. Er wird nach den aufgefundenen Dorsalklappen alsDiscinisca (Discradisca)littigensis n. sp. bestimmt und ist die älteste Art von 4 Disciniscen, die vom Golf, der Atlantischen Küstenebene und der Karibischen Region bekanntgeworden sind.Es wird vorgeschlagen, zwei neue Subgenera einzuführen:Discinisca s. s. undDiscradisca n. subgen. Die letztere basiert auf der Typen-ArtD. antillarum (D'Orbigny), die rezent von Kuba bis nach Brasilien vorkommt.Die geographische Verteilung der Gattung in Süd-, Mittel- und Nordamerika und ihr bathymetrischer Bereich werden diskutiert. In beiderlei Hinsicht streuen jedoch die Beobachtungswerte so stark, daß sie sich paläoökologisch nicht auswerten lassen.
Herrn Prof. Dr. Dr. h. c.Erich Bederke zum 70. Geburtstag gewidmet. 相似文献
Three species of brachiopods are found at the type locality of the Littig phosphorite-cobble paraconglomerate at the base of the Midway group (Danian). One of the three, a chitinophosphatic inarticulate brachiopod, is probably contemporaneous with the conglomerate. It is described from upper valves asDiscinisca (Discradisca) littigensis n. sp. and is the oldest of four Disciniscas known from the Gulf and the Atlantic Coastal Plains and the Caribbean region. Two subgenera are proposed:Discinisca s. s. andDiscradisca n. subgen. The latter is based on the type speciesD. antillarum (D'Orbigny), which is found living from Cuba to Brazil. The geographic distribution of the genus in the Americas and its bathymetric range are discussed with the conclusion that both the distribution and the range are too widespread to be useful in paleoecological interpretation.
Résumé Dans la localité — type du paraconglomérat de Littig à nodules de phosphorite, situé à la base du Midway group (Etage danien), on a trouvé trois espèces de brachiopodes. L'une, un brachiopode inarticulé à coquille cornée, a probablement le même âge que le conglomérat. D'après les valves dorsales trouvées il a été déterminé commeDiscinisca (Discradisca) littigensis n. sp. et constitue l'espèce la plus ancienne des 4 Disciniscées connues du Golfe, du littoral atlantique et de la région des Caraïbes.Il est proposé d'introduire deux nouveaux sous-genres:Discinisca s. s. etDiscradisca n. subgen. La dernière est basée sur l'espèce-typeD. antillarum (D'Orbigny) qui se rencontre à l'époque récente depuis Cuba jusqu'au Brésil. L'auteur discute la répartition géographique de l'espèce en Amérique méridionale, septentrionale et centrale, ainsi que son milieu bathymétrique. Considérées toutefois sous ce double aspect, les valeurs observées présentent tellement d'écart que l'on ne peut pas en tirer de conclusions au point de vue paléoécologique.
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Herrn Prof. Dr. Dr. h. c.Erich Bederke zum 70. Geburtstag gewidmet. 相似文献
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The engineering-geological environment, as any other geological environment, can be described by a number of variables. A clustering of those variables or clustering of their quantities makes it possible to divide the environment into taxonomic types. It is also possible to determine factors which are functions of those variables and which characterize the environment or its parts. In this paper we have applied R-and Q-mode factor analysis to engineering-geological research, concentrating our attention on establishing criteria for subdividing an environment into various aspects by its engineering-geological characteristics. 相似文献
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