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David Kappel - One of the best experts on this subject based on the ideXlab platform.
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probing Venus Surface iron contents with six band visible near infrared spectroscopy from orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Probing Venus Surface Iron Contents With Six‐Band Visible Near‐Infrared Spectroscopy From Orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Multi-spectrum retrieval of maps of Venus' Surface emissivity in the infrared
2015Co-Authors: David KappelAbstract:The main goal of this cumulative thesis is the derivation of Surface emissivity data in the infrared from radiance measurements of Venus. Since these data are diagnostic of the chemical composition and grain size of the Surface material, they can help to improve knowledge of the planet’s geology. Spectrally resolved images of nightside emissions in the range 1.0-5.1 μm were recently acquired by the InfraRed Mapping channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA’s Venus EXpress (VEX). Surface and deep atmospheric thermal emissions in this spectral range are strongly obscured by the extremely opaque atmosphere, but three narrow spectral windows at 1.02, 1.10, and 1.18 μm allow the sounding of the Surface. Additional windows between 1.3 and 2.6 μm provide information on atmospheric parameters that is required to interpret the Surface signals. Quantitative data on Surface and atmosphere can be retrieved from the measured spectra by comparing them to simulated spectra. A numerical radiative transfer model is used in this work to simulate the observable radiation as a function of atmospheric, Surface, and instrumental parameters. It is a line-by-line model taking into account thermal emissions by Surface and atmosphere as well as absorption and multiple scattering by gases and clouds. The VIRTIS-M-IR measurements are first preprocessed to obtain an optimal data basis for the subsequent steps. In this process, a detailed detector responsivity analysis enables the optimization of the data consistency. The measurement data have a relatively low spectral information content, and different parameter vectors can describe the same measured spectrum equally well. A usual method to regularize the retrieval of the wanted parameters from a measured spectrum is to take into account a priori mean values and standard deviations of the parameters to be retrieved. This decreases the probability to obtain unreasonable parameter values. The multi-spectrum retrieval algorithm MSR is developed to additionally consider physically realistic spatial and temporal a priori correlations between retrieval parameters describing different measurements. Neglecting geologic activity, MSR also allows the retrieval of an emissivity map as a parameter vector that is common to several spectrally resolved images that cover the same Surface target. Even applying MSR, it is difficult to obtain reliable emissivity maps in absolute values. A detailed retrieval error analysis based on synthetic spectra reveals that this is mainly due to interferences from parameters that cannot be derived from the spectra themselves, but that have to be set to assumed values to enable the radiative transfer simulations. The MSR retrieval of emissivity maps relative to a fixed emissivity is shown to effectively avoid most emissivity retrieval errors. Relative emissivity maps at 1.02, 1.10, and 1.18 μm are finally derived from many VIRTIS-M-IR measurements that cover a Surface target at Themis Regio. They are interpreted as spatial variations relative to an assumed emissivity mean of the target. It is verified that the maps are largely independent of the choice of many interfering parameters as well as the utilized measurement data set. These are the first Venus IR emissivity data maps based on a consistent application of a full radiative transfer simulation and a retrieval algorithm that respects a priori information. The maps are sufficiently reliable for future geologic interpretations.
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VIRTIS on Venus Express: retrieval of real Surface emissivity on global scales
Infrared Remote Sensing and Instrumentation XXIII, 2015Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Giuseppe Piccioni, Laura Tellez Pedroza, Pierre DrossartAbstract:The extraction of Surface emissivity data provides the data base for Surface composition analyses and enables to evaluate Venus’ geology. The Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express mission measured, inter alia, the nightside thermal emission of Venus in the near infrared atmospheric windows between 1.0 and 1.2 μm. These data can be used to determine information about Surface properties on global scales. This requires a sophisticated approach to understand and consider the effects and interferences of different atmospheric and Surface parameters influencing the retrieved values. In the present work, results of a new technique for retrieval of the 1.0 – 1.2 μm – Surface emissivity are summarized. It includes a Multi-Window Retrieval Technique, a Multi-Spectrum Retrieval technique (MSR), and a detailed reliability analysis. The MWT bases on a detailed radiative transfer model making simultaneous use of information from different atmospheric windows of an individual spectrum. MSR regularizes the retrieval by incorporating available a priori mean values, standard deviations as well as spatial-temporal correlations of parameters to be retrieved. The capability of this method is shown for a selected Surface target area. Implications for geologic investigations are discussed. Based on these results, the work draws conclusions for future Venus Surface composition analyses on global scales using spectral remote sensing techniques. In that context, requirements for observational scenarios and instrumental performances are investigated, and recommendations are derived to optimize spectral measurements for Venus’ Surface studies.
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Venus Surface and near Surface anomalies on the Northern hemisphere observed by VIRTIS/VEX: First results
2009Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Alexander T. Basilevsky, Pierre Drossart, Giuseppe PiccioniAbstract:Venus nightside emission measurements of VIRTIS on Venus Express provide the opportunity of Surface studies in the narrow near infrared atmospheric windows. The measurements as well as detailed new radiative transfer simulations show that radiance ratios in the emission windows between 1.0 and 1.35 micron with respect to the 1.02 micron window can be used to extract information about the Surface elevation and temperature. Based on these analyses, first Surface and near Surface anomalies are identified on the Northern hemisphere of Venus, which are due to deviations of the elevation - temperature correlation in certain small areas. The data are selected from VIRTIS-M-IR nightside measurements. To ensure minimal atmospheric influence on the measured signatures, only pushbroom observations with small observation angles close to nadir are taken into account. The radiative transfer simulation technique considers absorption, emission, and multiple scattering by gaseous and particulate constituents of the atmosphere. Look-up tables of quasi-monochromatic gas absorption cross-sections are calculated using appropriate spectral line data bases and line profiles and a line-by-line procedure. Empirical continuum absorption coefficients are determined from a ’VIRTIS reference spectrum’. In order to derive the parameters of the H2SO4 clouds, Mie theory is applied. Multiple scattering is considered by a Successive Order procedure. The synthetic quasi-monochromatic intensity spectra at the model top level of the atmosphere are convolved with the VIRTIS spectral response function. The Surface windows at 1.02, 1.10 and 1.18 micron exhibit a clear dependence of transmitted radiation on topographical features and, thus, on Surface thermal emission, since an elevation change of 12 km results in a temperature change of 100 K. In the first approximation, the radiance ratios are affine linear functions of the Surface temperature. This is demonstrated by both measurements and simulations. In general, the ratio-based VIRTIS topography correlates well with the Magellan topography, but differences occur in localized areas. Different local Surface anomalies do exist. These anomalies are probably a result of the lower atmosphere dynamics, errors in Magellan elevation determinations, or variations in the Surface emissivity. Surface emissivity variations are important indicators of the nature of Surface material. They may be due to variations in mineralogy and Surface texture. While most of Venus’ geologic units are thought to be basaltic in composition, some of them (tessera terrains) could be felsic. The 1 micron emissivity of felsic materials is lower compared to basalts at similar texture conditions. Nevertheless, we found that anomalous areas comprise practically the same geologic units as adjacent non-anomalous terrains. The Surface texture (grain size, packing density, Surface roughness) is another important factor for emissivity anomalies. Grain size affects the spectral characteristics. Laboratory measurements of basalts and oxidized basalts show significant changes in the contrast of the 1 micron reflectivity band. Although most of the Surface of Venus is not very rough, roughness variations exist. Tesserae and rifts show a higher Surface roughness compared to other areas. Finally, the Magellan radar data that represent the base of the topography information of the Venus Surface result from a Surface layer of about 1 m in thickness, whereas the VIRTIS-NIR data describe the optical upper Surface layer only. The radiative transfer simulations show the capability of our algorithm to investigate the Surface of Venus. Based on these simulations and the VIRTIS/VEX measurements, the extracted anomalies are discussed in the framework of these processes and influences mentioned above. Future improvements will contribute to eliminate the masking of the Venus nightside windows by far wing and pressure-induced absorptions of the deep atmosphere constituents. This will allow a better separation of deep atmosphere, temperature, and emissivity contributions to the Venus nightside emission.
Bruce Fegley - One of the best experts on this subject based on the ideXlab platform.
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chemistry of atmosphere Surface interactions on Venus and mars
Venus and Mars: Atntospheres Ionospheres and Solar Wind Interactions, 2013Co-Authors: Bruce Fegley, Allan H TreimanAbstract:Earth-based, earth-orbital, and spacecraft observational data are used in the present evaluation of Venus atmosphere-Surface interactions to quantitatively characterize the reactions between C, H, S, Cl, F, and N gases and plausible Surface minerals. Calculation results are used to predict stable minerals and mineral assemblages on the Venus Surface, in order to ascertain which (if any) of the atmospheric gases are buffeted by mineral assemblages. Chemical equilibrium calculations using extant thermodynamic data on scapolite minerals predict that carbonate-bearing scapolite and sulfate meionite are unstable on the Surface of Venus, while chloride-bearing scapolite is stable.
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Heavy metal frost on Venus
Icarus, 2004Co-Authors: Laura Schaefer, Bruce FegleyAbstract:Abstract Chemical equilibrium calculations of volatile metal geochemistry on Venus show that high dielectric constant compounds of lead and bismuth such as PbS (galena), Bi 2 S 3 (bismuthite) or Pb–Bi sulfosalts condense in the Venusian highlands and may be responsible for the low radar emissivities observed by Magellan and Pioneer Venus. Our calculations also show that elemental tellurium is unstable on Venus' Surface and will not condense below 46.6 km. This is over 30 km higher than Maxwell Montes, the highest point on Venus' Surface. Elemental analyses of Venus' highlands Surface by laser induced breakdown spectroscopy (LIBS) and/or X-ray fluorescence (XRF) can verify the identity of the heavy metal frost on Venus. The Pb–Pb age of Venus could be determined by mass spectrometric measurements of the Pb 207 /Pb 204 and Pb 206 /Pb 204 isotopic ratios in Pb-bearing frosts. All of these measurements are technologically feasible now.
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Iron Mineralogy of Venus' Surface Investigated by Mössbauer Spectroscopy
Icarus, 2000Co-Authors: Göstar Klingelhöfer, Bruce FegleyAbstract:Abstract We discuss the use of Mossbauer (MB) spectroscopy to study Fe-bearing minerals on Venus' Surface. At present, there is no direct information about the mineralogy of Venus' Surface, although in situ chemical analyses by X-ray fluorescence (XRF) spectroscopy have been done by the Venera 13, 14, and Vega 2 spacecraft at three landing sites. The XRF elemental analyses are sensitive to major rock-forming elements heavier than sodium and show the presence of several mass percent iron. Normative mineralogical calculations model the Fe mineralogy at the Venera 13, 14, and Vega 2 landing sites, but the actual Fe minerals present are unknown. We calculate synthetic MB spectra for the normative Fe minerals at the Venera 14 and Vega 2 landing sites. Some calculations include several mass percent of the Fe oxides (magnetite, hematite) and sulfides (pyrite, pyrrhotite) that are frequently discussed in the literature as being present on Venus' Surface. Our results indicate that the normative iron minerals at the different landing sites can be identified, quantitatively measured, and distinguished from each other using MB spectroscopy. We also find that about 1 mass percent of any of the different iron oxides and sulfides considered in our modeling should be detectable using MB spectroscopy. This is significant because the loaded dielectric model for low radar emissivity regions on Venus requires several mass percent of Fe-bearing phases. The temperature dependence of the MB spectra is also calculated. Finally, the implications of these results for future spacecraft missions to Venus using MB spectroscopy are discussed.
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Stability of micas on the Surface of Venus
Planetary and Space Science, 1998Co-Authors: M.yu Zolotov, Bruce Fegley, Katharina LoddersAbstract:Abstract Recent thermodynamic modeling shows that some micas might be stable on VenusSurface. However, prior studies considered only pure micas and did not consider mica solidsolutions, which are commonly observed on Earth. Here we use chemical equilibriumcalculations to evaluate the stability of mica solid solutions on Venus Surface as a function ofatmospheric chemistry (H2O and HF abundances, and redox state), and Surface elevation. Ourprior calculations show that the end-member micas eastonite (KMg2Al3Si2O10(OH)2) andfluorphlogopite (KMg3AlSi3O10F2) are stable on Venus Surface, while the end-member micasphlogopite (KMg3AlSi3O10(OH)2), annite (KFe3AlSi3O10(OH)2), and siderophyllite (KFe2+2Al3Si2O10(OH)2) are unstable. Based on these results and known petrologic phase relationships, weconsider binary solutions of eastonite with either phlogopite or siderophyllite, andfluorphlogopite with phlogopite. We calculate that micas along all three binaries are stable onVenus. Micas containing ∼20 mole% eastonite and ∼80% phlogopite are stable in the lowertemperature highlands, and very eastonite-rich micas are stable over Venus entire Surface.Fluorphlogopite-rich micas are also stable over Venus Surface, while fluorphlogopite-poor micasare stable at higher elevations. Iron-poor micas along the eastonite-siderophyllite join, containing>80 mole% eastonite, are stable in both the highlands and lowlands. Finally, we use thethermodynamic calculations, terrestrial geology, and petrologic phase equilibria to discussplausible geological settings where micas may be present on Venus. These suggestions areimportant for the design of geochemical experiments on future lander and automated balloonmissions to Venus.
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The sulfur vapor pressure over pyrite on the Surface of Venus
Planetary and Space Science, 1998Co-Authors: Yong Hong, Bruce FegleyAbstract:Abstract The total pressure and molecular speciation of sulfur vapor (dominantly S2) over pyrite at Venus Surface temperatures (≈ 390–470°C) are important for modeling atmospheric chemistry and geochemistry of sulfur gases and minerals on Venus. The sulfur vapor pressure over pyrite in CO2 and CO2 gas mixtures, which are relevant to Venus, has not been previously measured. Instead, previous measurements were generally done in closed systems, such as sealed, evacuated silica tubes. We measured the sulfur vapor pressure over pyrite in an open system where carrier gas is flowing through a gas mixing furnace, from 441 to 591°C in He, N2, CO2, and CO2SO2CO mixtures using a standard technique, the transpiration method (Merton, U. and Bell, W. E. (1967) The transpiration method. In The Characterization of High Temperature Vapors, ed. J. W. Margrave, pp. 91–114. Wiley, New York). The data show that the sulfur vapor pressure over pyrite is the same in inert gas and in CO2-bearing gases. Our data also agree with literature vapor pressure data. Thermodynamic calculations show that the laboratory vapor pressure data are also valid at Venus Surface pressures (≈ 50–100 bar). Finally, we present recommended values for the sulfur vapor pressure and calculate the molecular speciation of sulfur vapor over pyrite at Venus Surface temperatures.
M. D. Dyar - One of the best experts on this subject based on the ideXlab platform.
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Deriving iron contents from past and future Venus Surface spectra with new high-temperature laboratory emissivity data.
Science advances, 2021Co-Authors: J Helbert, M. D. Dyar, A Maturilli, G AlemannoAbstract:In situ information on the Surface composition of Venus is based on measurements of a small number of landing sites. In the laboratory, we measured the emissivity of a range of igneous rocks at temperatures up to 480°C. We show that high-temperature laboratory spectra of basalts are consistent with the only existing multispectral data from the Surface of Venus obtained by the photometers on the Venera 9 and 10 landers. We derive the FeO abundances for these landing sites of 12.2 and 9.5 weight %, respectively. From orbit, Venus' Surface is only observable on the nightside through small spectral windows near 1 μm where the CO2 atmosphere is largely transparent. The new laboratory data show that different rock types can be distinguished using only a small set of spectral bands. Therefore, future orbital spectral observations can provide a much-needed global composition map.
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probing Venus Surface iron contents with six band visible near infrared spectroscopy from orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Probing Venus Surface Iron Contents With Six‐Band Visible Near‐Infrared Spectroscopy From Orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Probing Rock Type, Fe Redox State, and Transition Metal Contents with Six-Window VNIR Spectroscopy Under Venus Conditions
2017Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, T. Widemann, T. Boucher, Dennis Wendler, Ingo Walter, Emmanuel Marcq, Sabrina Ferrari, Mario D'amoreAbstract:VEM-window data are shown to distinguish among key rock types on Venus, and evaluate redox state and transition metal contents of Venus Surface rocks.
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Remote Raman-Laser Induced Breakdown Spectroscopy (LIBS) Geochemical Investigation Under Venus Atmospheric Conditions
2010Co-Authors: Samuel M. Clegg, M. D. Dyar, S. K. Sharma, A. K. Misra, M. H. Hecht, J. Lambert, S. M. Feldman, N. Dallmann, R. C. Wiens, S. D. HumphriesAbstract:The extreme Venus Surface temperatures ({approx}740 K) and atmospheric pressures ({approx}93 atm) create a challenging environment for Surface missions. Scientific investigations capable of Venus geochemical observations must be completed within hours of landing before the lander will be overcome by the harsh atmosphere. A combined remote Raman - LIBS (Laser Induced Breakdown Spectroscopy) instrument is capable of accomplishing the geochemical science goals without the risks associated with collecting samples and bringing them into the lander. Wiens et al. and Sharma et al. demonstrated that both analytical techniques can be integrated into a single instrument capable of planetary missions. The focus of this paper is to explore the capability to probe geologic samples with Raman - LIBS and demonstrate quantitative analysis under Venus Surface conditions. Raman and LIBS are highly complementary analytical techniques capable of detecting both the mineralogical and geochemical composition of Venus Surface materials. These techniques have the potential to profoundly increase our knowledge of the Venus Surface composition, which is currently limited to geochemical data from Soviet Venera and VEGA landers that collectively suggest a Surface composition that is primarily tholeiitic basaltic with some potentially more evolved compositions and, in some locations, K-rich trachyandesite. These landers were notmore » equipped to probe the Surface mineralogy as can be accomplished with Raman spectroscopy. Based on the observed compositional differences and recognizing the imprecise nature of the existing data, 15 samples were chosen to constitute a Venus-analog suite for this study, including five basalts, two each of andesites, dacites, and sulfates, and single samples of a foidite, trachyandesite, rhyolite, and basaltic trachyandesite under Venus conditions. LIBS data reduction involved generating a partial least squares (PLS) model with a subset of the rock powder standards to quantitatively determine the major elemental abundance of the remaining samples. PLS analysis suggests that the major element compositions can be determined with root mean square errors ca. 5% (absolute) for SiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3}(total), MgO, and CaO, and ca. 2% or less for TiO{sub 2}, Cr{sub 2}O{sub 3}, MnO, K{sub 2}O, and Na{sub 2}O. Finally, the Raman experiments have been conducted under supercritical CO{sub 2} involving single-mineral and mixed-mineral samples containing talc, olivine, pyroxenes, feldspars, anhydrite, barite, and siderite. The Raman data have shown that the individual minerals can easily be identified individually or in mixtures.« less
Jörn Helbert - One of the best experts on this subject based on the ideXlab platform.
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probing Venus Surface iron contents with six band visible near infrared spectroscopy from orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Probing Venus Surface Iron Contents With Six‐Band Visible Near‐Infrared Spectroscopy From Orbit
Geophysical Research Letters, 2020Co-Authors: M. D. Dyar, Jörn Helbert, Alessandro Maturilli, Nils Müller, David KappelAbstract:Machine learning models enable interpretation of orbital spectral measurements of Venus using laboratory calibration data collected at Venus Surface temperatures. Partial least squares models show that total iron content can be accurately predicted using data from the six bands (two in the 1.02 μm window). Prediction errors on total wt% FeO are ±0.50 for common subalkaline volcanic rocks. Accuracy is ±0.42 for wt% FeO in alkaline rocks, and ±2.47 for all 18 igneous samples studied to date. These robust capabilities will allow discrimination of basalt versus rhyolite/granite and elucidate the rock type of the enigmatic tessera terrain on Venus.
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Venus Surface Composition Constrained by Observation and Experiment
Space Science Reviews, 2017Co-Authors: Martha Gilmore, Jörn Helbert, Allan Treiman, Suzanne SmrekarAbstract:New observations from the Venus Express spacecraft as well as theoretical and experimental investigation of Venus analogue materials have advanced our understanding of the petrology of Venus melts and the mineralogy of rocks on the Surface. The VIRTIS instrument aboard Venus Express provided a map of the southern hemisphere of Venus at ∼1 μm allowing, for the first time, the definition of Surface units in terms of their 1 μm emissivity and derived mineralogy. Tessera terrain has lower emissivity than the presumably basaltic plains, consistent with a more silica-rich or felsic mineralogy. Thermodynamic modeling and experimental production of melts with Venera and Vega starting compositions predict derivative melts that range from mafic to felsic. Large volumes of felsic melts require water and may link the formation of tesserae to the presence of a Venus ocean. Low emissivity rocks may also be produced by atmosphere-Surface weathering reactions unlike those seen presently. High 1 μm emissivity values correlate to stratigraphically recent flows and have been used with theoretical and experimental predictions of basalt weathering to identify regions of recent volcanism. The timescale of this volcanism is currently constrained by the weathering of magnetite (higher emissivity) in fresh basalts to hematite (lower emissivity) in Venus’ oxidizing environment. Recent volcanism is corroborated by transient thermal anomalies identified by the VMC instrument aboard Venus Express. The interpretation of all emissivity data depends critically on understanding the composition of Surface materials, kinetics of rock weathering and their measurement under Venus conditions. Extended theoretical studies, continued analysis of earlier spacecraft results, new atmospheric data, and measurements of mineral stability under Venus conditions have improved our understanding atmosphere-Surface interactions. The calcite-wollastonite CO_2 buffer has been discounted due, among other things, to the rarity of wollastonite and instability of carbonate at the Venus Surface. Sulfur in the Venus atmosphere has been shown experimentally to react with Ca in Surface minerals to produce anhydrite. The extent of this SO_2 buffer is constrained by the Ca content of Surface rocks and sulfur content of the atmosphere, both of which are likely variable, perhaps due to active volcanism. Experimental work on a range of semiconductor and ferroelectric minerals is placing constraints on the cause(s) of Venus’ anomalously radar bright highlands.
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Venus Surface Composition Constrained by Observation and Experiment
Space Science Reviews, 2017Co-Authors: Martha S. Gilmore, Allan H Treiman, Jörn Helbert, Suzanne E. SmrekarAbstract:New observations from the Venus Express spacecraft as well as theoretical and experimental investigation of Venus analogue materials have advanced our understanding of the petrology of Venus melts and the mineralogy of rocks on the Surface. The VIRTIS instrument aboard Venus Express provided a map of the southern hemisphere of Venus at ∼1 μm allowing, for the first time, the definition of Surface units in terms of their 1 μm emissivity and derived mineralogy. Tessera terrain has lower emissivity than the presumably basaltic plains, consistent with a more silica-rich or felsic mineralogy. Thermodynamic modeling and experimental production of melts with Venera and Vega starting compositions predict derivative melts that range from mafic to felsic. Large volumes of felsic melts require water and may link the formation of tesserae to the presence of a Venus ocean. Low emissivity rocks may also be produced by atmosphere-Surface weathering reactions unlike those seen presently.
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SO2 Vapor Equilibrium with Oxidized Surface Rocks
2017Co-Authors: T. Widemann, Jörn Helbert, James W. Head, S.e. SmrekarAbstract:Weathering reactions on Venus' Surface can be characterized from orbit using band ratios from thermal emissivity data in combination with radar emissivity.
Gabriele Arnold - One of the best experts on this subject based on the ideXlab platform.
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VIRTIS on Venus Express: retrieval of real Surface emissivity on global scales
Infrared Remote Sensing and Instrumentation XXIII, 2015Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Giuseppe Piccioni, Laura Tellez Pedroza, Pierre DrossartAbstract:The extraction of Surface emissivity data provides the data base for Surface composition analyses and enables to evaluate Venus’ geology. The Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express mission measured, inter alia, the nightside thermal emission of Venus in the near infrared atmospheric windows between 1.0 and 1.2 μm. These data can be used to determine information about Surface properties on global scales. This requires a sophisticated approach to understand and consider the effects and interferences of different atmospheric and Surface parameters influencing the retrieved values. In the present work, results of a new technique for retrieval of the 1.0 – 1.2 μm – Surface emissivity are summarized. It includes a Multi-Window Retrieval Technique, a Multi-Spectrum Retrieval technique (MSR), and a detailed reliability analysis. The MWT bases on a detailed radiative transfer model making simultaneous use of information from different atmospheric windows of an individual spectrum. MSR regularizes the retrieval by incorporating available a priori mean values, standard deviations as well as spatial-temporal correlations of parameters to be retrieved. The capability of this method is shown for a selected Surface target area. Implications for geologic investigations are discussed. Based on these results, the work draws conclusions for future Venus Surface composition analyses on global scales using spectral remote sensing techniques. In that context, requirements for observational scenarios and instrumental performances are investigated, and recommendations are derived to optimize spectral measurements for Venus’ Surface studies.
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Venus Surface and near Surface anomalies on the Northern hemisphere observed by VIRTIS/VEX: First results
2009Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Alexander T. Basilevsky, Pierre Drossart, Giuseppe PiccioniAbstract:Venus nightside emission measurements of VIRTIS on Venus Express provide the opportunity of Surface studies in the narrow near infrared atmospheric windows. The measurements as well as detailed new radiative transfer simulations show that radiance ratios in the emission windows between 1.0 and 1.35 micron with respect to the 1.02 micron window can be used to extract information about the Surface elevation and temperature. Based on these analyses, first Surface and near Surface anomalies are identified on the Northern hemisphere of Venus, which are due to deviations of the elevation - temperature correlation in certain small areas. The data are selected from VIRTIS-M-IR nightside measurements. To ensure minimal atmospheric influence on the measured signatures, only pushbroom observations with small observation angles close to nadir are taken into account. The radiative transfer simulation technique considers absorption, emission, and multiple scattering by gaseous and particulate constituents of the atmosphere. Look-up tables of quasi-monochromatic gas absorption cross-sections are calculated using appropriate spectral line data bases and line profiles and a line-by-line procedure. Empirical continuum absorption coefficients are determined from a ’VIRTIS reference spectrum’. In order to derive the parameters of the H2SO4 clouds, Mie theory is applied. Multiple scattering is considered by a Successive Order procedure. The synthetic quasi-monochromatic intensity spectra at the model top level of the atmosphere are convolved with the VIRTIS spectral response function. The Surface windows at 1.02, 1.10 and 1.18 micron exhibit a clear dependence of transmitted radiation on topographical features and, thus, on Surface thermal emission, since an elevation change of 12 km results in a temperature change of 100 K. In the first approximation, the radiance ratios are affine linear functions of the Surface temperature. This is demonstrated by both measurements and simulations. In general, the ratio-based VIRTIS topography correlates well with the Magellan topography, but differences occur in localized areas. Different local Surface anomalies do exist. These anomalies are probably a result of the lower atmosphere dynamics, errors in Magellan elevation determinations, or variations in the Surface emissivity. Surface emissivity variations are important indicators of the nature of Surface material. They may be due to variations in mineralogy and Surface texture. While most of Venus’ geologic units are thought to be basaltic in composition, some of them (tessera terrains) could be felsic. The 1 micron emissivity of felsic materials is lower compared to basalts at similar texture conditions. Nevertheless, we found that anomalous areas comprise practically the same geologic units as adjacent non-anomalous terrains. The Surface texture (grain size, packing density, Surface roughness) is another important factor for emissivity anomalies. Grain size affects the spectral characteristics. Laboratory measurements of basalts and oxidized basalts show significant changes in the contrast of the 1 micron reflectivity band. Although most of the Surface of Venus is not very rough, roughness variations exist. Tesserae and rifts show a higher Surface roughness compared to other areas. Finally, the Magellan radar data that represent the base of the topography information of the Venus Surface result from a Surface layer of about 1 m in thickness, whereas the VIRTIS-NIR data describe the optical upper Surface layer only. The radiative transfer simulations show the capability of our algorithm to investigate the Surface of Venus. Based on these simulations and the VIRTIS/VEX measurements, the extracted anomalies are discussed in the framework of these processes and influences mentioned above. Future improvements will contribute to eliminate the masking of the Venus nightside windows by far wing and pressure-induced absorptions of the deep atmosphere constituents. This will allow a better separation of deep atmosphere, temperature, and emissivity contributions to the Venus nightside emission.
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Venus Surface data extraction from VIRTIS/VEX measurements
2008Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Pierre Drossart, Giuseppe Piccioni, Wolfgang Döhler, Virtis, Vex TeamAbstract:The capability of near infrared nightside thermal emission measurements by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express (VEX) was used to extract Surface properties in the northern hemisphere of Venus. The study includes VIRTIS topographic footprint variations from – 2000 m to 6000 m in height. Preliminary radiative transfer calculation techniques were applied to simulate Venus nightside radiation with respect to the cloud opacity and Surface elevation. The results were compared to the VIRTIS measurements. Below 1.5 µm conservative scattering is dominating the cloud feature, Therefore, radiance ratios in the 1.0-1.35 µm spectral windows can be used to eliminate cloud interferences. It is shown that the radiance ratios of the 1.10, 1.18, 1.28, and 1.31 µm windows with respect to the radiance in the 1.02 µm window are independent on the cloud influence. At constant cloud opacity the simulations at 1.02, 1.10, and 1.18 µm show a clear dependence of the transmitted nightside radiation on topography. An elevation change of 12 km results in a Surface temperature change of 100 K. The measured and simulated window radiance ratios are in excellent agreement. The correlation between the ratios of the Surface window radiances and elevations was used to retrieve the Surface topography and temperatures near Beta region. VIRTIS and Magellan topographies are largely in agreement to each other but differences are obtained in certain small areas. They will be of special interest for the future separation of Surface temperature, emissivity and deep atmosphere dynamic phenomena.
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Venus Surface investigation based on VIRTIS measurements on Venus Express
2008Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, Pierre Drossart, Wolfgang Döhler, Virtis, Guiseppe Piccioni, Vex TeamAbstract:The dense atmosphere of Venus prevented systematic studies of its Surface at optical wavelengths in the past. The discovery of near infrared nightside atmospheric windows has opened a new challenge for detailed Surface studies. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express is the first experiment collecting continuously nightside Surface emission data from the planet. The observed high variability of measured signatures is mainly due to spatial variations of cloud optical depth and Surface elevation. The investigation of Surface properties requires a convergent approach of radiative transfer simulations and VIRTIS data analyses. Therefore, a selection of orbits with well calibrated data over the northern hemisphere was performed for footprints that cover a maximum range of Surface elevation variations. Radiative transfer calculations demonstrate that the conservative character of cloud multiple scattering below 2 µm and a strong dependence of radiance ratios on Surface elevation in this spectral region allow the mapping of Surface topography and a retrieval of the Surface temperature. To the first order, the Surface temperature is a function of ground elevation. Small deviations from this first order dependence have been identified that are possibly due to different Surface materials.
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Venus Surface data extraction from virtis Venus express measurements estimation of a quantitative approach
Journal of Geophysical Research, 2008Co-Authors: Gabriele Arnold, David Kappel, Rainer Haus, P Drossart, Guiseppe PiccioniAbstract:Nightside emission measurements of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the Venus Express (VEX) spacecraft were used to estimate the potential for Surface data extraction. A selection of orbits over the northern hemisphere was performed for footprints that cover different scales of Surface elevation variations. A correction method was used to remove straylight from the measured spectra that is due to direct sunlight striking the instrument. A preliminary radiative transfer calculation technique was applied to simulate Venus nightside radiation. The basic features of the measured spectra are well reproduced. Present limitations of the algorithm are discussed. The variability of the emission window radiances with respect to cloud opacity and Surface elevation is modelled and discussed in direct comparison with the measurements. It is demonstrated that a multi-spectral analysis in the Surface and deep atmosphere window ranges (1.0-2.3 µm) and the use of radiance ratios are well suited to de-cloud the data and to extract Surface information from the VIRTIS measurements. This method allows a mapping of Surface topography and the retrieval of the Surface temperature. A preliminary topography retrieval at Beta Regio was performed and compared with Magellan radar data. Differences are possibly due to emissivity variations on the Surface.
