Methane on Mars: new insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of t...

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Autores: Liuzzi, Giuliano, Villanueva, Geronimo L., Mumma, M.J., Smith, M. D., Daerden, Frank, Ristic, Bojan, Thomas, Ian R., Vandaele, Ann Carine, Patel, Manish R., López-Moreno, José Juan, Bellucci, Giancarlo, Allen, M., Alonso-Rodrigo, G., Altieri, F., Aoki, Shohei, Bauduin, S., Bolsée, D., Clancy, T., Cloutis, E., D'Aversa, Emiliano, Depiesse, C., Erwin, Justin T., Fedorova, A., Formisano, V., Funke, Bernd, Fussen, D., García Comas, Maia, Geminale, A., Gérard, Jean-Claude, Gillotay, D., Giuranna, M., González-Galindo, F., Hewson, W., Homes, J., Ignatiev, N., Kaminski, J., Karatekin, O., Kasaba, Y., Lanciano, O., Lefèvre, F., Lewis, S., López-Puertas, Manuel, López-Valverde, M. A., Mahieux, A., Mason, J., Mc Connell, J., Hiromu Neary Nakagawa, L., Neefs, E., Novak, R., Oliva, F., Piccialli, A., Renotte, E., Robert, S., Sindoni, G., Stiepen, A., Trokhimovskiy, A., Vander Auwera, J., Viscardy, S., Whiteway, J., Willame, Y., Wilquet, V., Wolff, Michael T., Wolkenberg, P., Aparicio del Moral, Beatriz, Barzin, P., Beeckman, B., BenMoussa, A., Berkenbosch, S., Biondi, D., Bonnewijn, S., Candini, G. P., Clairquin, R., Cubas, J., Giordanengo, B., Gissot, Samuel, Gomez, A., Hathi, B., Jeronimo Zafra, J., Leese, M., Maes, J., Mazy, E., Mazzoli, A., Meseguer, J., Morales, Rafael, Orban, A., Pastor, Carmen, Pérez Grande, Isabel, Queirolo, C., Rodríguez Gómez, Julio, Saggin, B., Samain, V., Sanz Andres, A., Sanz Mesa, Rosario, Simar, J.-F., Thibert, Tanguy
Tipo de recurso: artículo
Estado:Versión enviada para evaluación y publicación
Fecha de publicación:2019
País:España
Institución:Consejo Superior de Investigaciones Científicas (CSIC)
Repositorio:DIGITAL.CSIC. Repositorio Institucional del CSIC
OAI Identifier:oai:digital.csic.es:10261/190687
Acceso en línea:http://hdl.handle.net/10261/190687
Access Level:acceso abierto
Palabra clave:Methane
NOMAD
Infrared spectroscopy
Instrumentation
Mars atmosphere
Descripción
Sumario:The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.© 2018 Elsevier Inc.

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