The Ultraviolet and Visible Spectrometer (UVIS) instrument development process requires the construction of an atmospheric model to provide synthetic UV transmission spectra. We discuss the requirements of the model to enable observational limits to be found, and the potential for certain atmospheric parameters to be further constrained

Dawson, D. G.

Lewis, S. R.

Patel, M. R.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsAtmospheric modelling for NOMAD-UVIS on boardthe ExoMars Trace Gas Orbiter missionConference or Workshop ItemHow to cite:Dawson, D. G.; Patel, M. R. and Lewis, S. R. (2012). Atmospheric modelling for NOMAD-UVIS on boardthe ExoMars Trace Gas Orbiter mission. In: EPSC 2012, 23-28 Sep 2012, Madrid, Spain.For guidance on citations see FAQs.c© 2012 The AuthorsVersion: Version of RecordLink(s) to article on publisher’s website:http://meetingorganizer.copernicus.org/EPSC2012/EPSC2012-180.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukAtmospheric modelling for NOMAD-UVIS on board theExoMars Trace Gas Orbiter missionD. G. Dawson, M. R. Patel and S. R. LewisDepartment of Physical Sciences, The Open University, UK (daniel.dawson@open.ac.uk)AbstractThe Ultraviolet and Visible Spectrometer (UVIS) in-strument development process requires the construc-tion of an atmospheric model to provide synthetic UVtransmission spectra. We discuss the requirements ofthe model to enable observational limits to be found,and the potential for certain atmospheric parameters tobe further constrained.1. IntroductionThe Nadir and Occultation for MArs Discovery (NO-MAD) instrument is currently being developed for theExoMars Trace Gas Orbiter mission. In preparationa radiative transfer model is being constructed to pro-vide synthetic spectra, to simulate the observations ofthe UV channel.Using spectroscopy to study atmospheric con-stituents has been a widely used technique for manydecades. It is by using this method we learn the com-position of non-terrestrial atmospheres. Spectrometerscan either be Earth bound, or sent on spacecraft for re-mote observations. Observatories on Earth, such as theNASA Infrared Telescope Facility in Hawaii providelong term observations to compliment the remotely re-covered data [1]. Other bodies can be observed froma lander on the surface, or from an orbital position.Mars has been observed in this way since the days ofMariner, and most recently with the SPICAM instru-ment on board Mars Express [2].2. RationaleWe currently have a limited understanding of manyfeatures of the atmosphere of Mars, specifically dustand aerosols. The parameters describing the sizedistribution, vertical distribution and composition ofdust require further investigation, although estimationshave been made [3, 4]. Based on certain assumptionswe have potential values for the dust optical proper-ties of single scattering albedo and the asymmetry fac-Figure 1: Overview of NOMAD, the UVIS channel isthe lower right hole and periscope.tor [5], although more time has been spent investigat-ing these for visible and IR wavelengths as opposedto UV. Better estimates of these parameters leads tobetter characterization of dust for global climate mod-elling and to a better understanding of dust composi-tion, shape and population and so its role in the martianclimate system. This would benefit future missions,for example through improved accuracy of aerobreak-ing calculations.Another atmospheric constituent active at shorterwavelengths is ozone. We have some idea of whenand where ozone is found, but predictions do not al-ways match observations [6, 7]. Further sensitive mea-surements will continue to aid our understanding ofhow ozone behaves on Mars, expanding the spatial andtemporal data set to increase our understanding of thesystem as a whole.3. The UVIS instrumentThe ExoMars TGO is planned for a 2016 launch. Onboard will be UVIS, an ultra violet and visible lightEPSC AbstractsVol. 7 EPSC2012-180 2012European Planetary Science Congress 2012c© Author(s) 2012EPSCEuropean Planetary Science Congressspectrometer forming part of the NOMAD instrument.UVIS will take frequent, high resolution (1 nm) spec-tra in both nadir and occultation viewing orientationsover the wavelength range of 200 - 650 nm. Thesehighly resolved spectra will improve analysis of manyatmospheric features, for example the Hartley bandof ozone absorption which requires accurate measure-ment. As a significant absorber of UV, determiningthe spatiotemporal distribution of ozone will assist inquantifying the amount of UV radiation reaching thesurface. This needs to be known due to the damagingeffect short wavelength radiation could have on poten-tial life [8]. The instrument will also be able to detectthe presence of clouds.Figure 2: Overview of the UVIS instrument, showingthe two measurement modes of solar occultation andnadir.4. The modelA forward model will be used to solve this inverseproblem of atmospheric retrievals. Existing core radia-tive transfer code will be modified to simulate variousdust loading scenarios, cloud formations and viewinggeometries as accurately as possible. The latest ex-perimental results will be used where appropriate, forexample molecular absorption cross sections will beneeded for all relevant gases.The model will also provide details of detection lim-its for a given set of climatic conditions, for examplethe lowest operational altitude achievable during oc-cultation measurements. In addition the model will al-low constraints to be placed on certain parameters ordistributions, such as the vertical distribution of dust.The aim of this work is to both assist the instru-ment team and to constrain parameters through spec-tral analysis of different atmospheric scenarios in or-der to maximise the scientific outputs from the instru-ment data.AcknowledgementsThis work has been supported by the UK Science andTechnology Facilities Council.References[1] Fast, K., Kostiuk, T., Espenak, F., Annen, J., Buhl, D.,Hewagama, T., A’Hearn, M. F., Zipoy, D., Livengood,T.A., Sonnabend, G. and Schmülling, F.: Ozone abun-dance on Mars from infrared heterodyne spectra: I. Ac-quisition, retrieval, and anticorrelation with water vapor,Icarus, Vol. 181, Issue 2, pp. 419-431, 2006.[2] Bertaux, J.-L., et al.: SPICAM on Mars Express: Ob-serving modes and overview of UV spectrometer dataand scientific results, J. Geophys. Res., Vol. 111, E10S90,2006.[3] Smith M. D.: Spacecraft Observations of the MartianAtmosphere, Annu. Rev. Earth Planet. Sci., Vol. 36, pp.191-219, 2008.[4] Kahre, M. A., Hollingsworth, J. L., Haberle, R. M. andMurphy, J. R.: Investigations of the variability of dustparticle sizes in the martian atmosphere using the NASAAmes General Circulation Model, Icarus, Vol. 195, Issue2, pp. 576-597, 2008.[5] Wolff, M. J., Clancy, R. T., Goguen, J. D., Malin, M. C.and Cantor, B. A.: Ultraviolet dust aerosol properties asobserved by MARCI, Icarus, Vol. 208, Issue 1, pp. 143-155, 2010.[6] Lefèvre, F., Lebonnois, S., Montmessin, F. and Forget,F.: Three-dimensional modeling of ozone on Mars, J.Geophys. Res., Vol. 109, E07004, 2004.[7] Perrier, S., Bertaux, J. L., Lefèvre, F., Lebonnois, S.,Korablev, O., Fedorova, A. and Montmessin, F.: Globaldistribution of total ozone on Mars from SPICAM/MEXUV measurements, J. Geophys. Res., Vol. 111, E09S06,2006.[8] Margulis, L., Walker, J. C. G. and Rambler, M.: Re-assessment of roles of oxygen and ultraviolet light in Pre-cambrian evolution, Nature, Vol. 264, pp. 620-624, 1976.

Atmospheric modelling for NOMAD-UVIS on board the ExoMars Trace Gas Orbiter mission

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Atmospheric modelling for NOMAD-UVIS on board the ExoMars Trace Gas Orbiter mission

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