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Christoph Wagner

Bio: Christoph Wagner is an academic researcher. The author has contributed to research in topics: Particle size & Grain size. The author has an hindex of 1, co-authored 1 publications receiving 12 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the experimentally found variation of spectral features with particle size is discussed in terms of photon's mean free path and its dependence on particle size in the wavelength regions characterized by normal and anomalous dispersion, respectively.
Abstract: Measurements of spectral emittance at wavelengths from 5 to 25 Μm were carried out for various particulate rocks and minerals (granite, calcite, talk) in dependence on particle size. The experimentally found variation of spectral features with particle size is discussed in terms of photon's mean free path and its dependence on particle size in the wavelength regions characterized by normal and anomalous dispersion, respectively. Moreover, a sample consisting of fine- and coarse-grained material was investigated in order to estimate the chance for mineral identification at conditions relevant to remote sensing of planetary objects. The mixture spectrum comprises characteristic features of both grain size fractions. This implies that the mineralogical composition of the fine-grained fraction also should be accessible by use of high-sensitive spectrometers.

13 citations


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04 Oct 2009
TL;DR: In this article, the authors present a review of vector calculus and functions of a complex variable and Fraunhoffer diffraction by a circular hole, and a miscellany of bidirectional reflectances and related quantities.
Abstract: Acknowledgements 1. Introduction 2. Electromagnetic wave propagation 3. The absorption of light 4. Specular reflection 5. Single particle scattering: perfect spheres 6. Single particle scattering: irregular particles 7. Propagation in a nonuniform medium: the equation of radiative transfer 8. The bidirectional reflectance of a semi-infinite medium 9. The opposition effect 10. A miscellany of bidirectional reflectances and related quantities 11. Integrated reflectances and planetary photometry 12. Photometric effects of large scale roughness 13. Polarization 14. Reflectance spectroscopy 15. Thermal emission and emittance spectroscopy 16. Simultaneous transport of energy by radiation and conduction Appendix A. A brief review of vector calculus Appendix B. Functions of a complex variable Appendix C. The wave equation in spherical coordinates Appendix D. Fraunhoffer diffraction by a circular hole Appendix E. Table of symbols Bibliography Index.

1,951 citations

Journal ArticleDOI
TL;DR: In this article, the authors show that the spectral properties of the PFS and TES data are consistent with tectosilicates, especially feldspars/feldspathoids, particularly in the area northeast of Stickney.

55 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the spectra of asteroids, absolutely calibrated through reference stars, with standard thermal models and thermophysical models for these bodies, using continuous 5-14 microns airborne spectra provided complete sampling of the rise to and peak, of the infrared spectral energy distribution and constrains these models.
Abstract: We describe our efforts to seek "closure" in our infrared absolute calibration scheme by comparing spectra of asteroids, absolutely calibrated through reference stars, with "Standard Thermal Models" and "Thermophysical Models" for these bodies. Our use of continuous 5-14 microns airborne spectra provides complete sampling of the rise to, and peak, of the infrared spectral energy distribution and constrains these models. Such models currently support the absolute calibration of ISO-PHOT at far-infrared wave- lengths (as far as 300 microns), and contribute to that of the Mid-Infrared Spectrometer on the "Infrared Telescope in Space" in the 6-12 microns region. The best match to our observed spectra of Ceres and Vesta is a, standard thermal model using a beaming factor of unity. We also report the presence of three emissivity features in Ceres which may complicate the traditional model extrapolation to the far-infrared from contemporaneous ground-based N-band photometry that is used to support calibration of, for example, ISO-PHOT. While identification of specific materials that cause these features is not made, we discuss families of minerals that may be responsible.

53 citations

Journal ArticleDOI
01 Aug 1992-Icarus
TL;DR: Global Martian atmospheric results derived from the infrared imaging spectrometer ISM flown aboard the Phobos 2 Soviet spacecraft are presented and suggest a strong interaction between the surface and the atmosphere for the Great Martian Volcanoes.

46 citations