Use of TGO-NOMAD nadir observations for ices detection

Ruiz Lozano, L. (1,2), Karatekin, Ö. (2), Caldiero, A. (2), Imbreckx, A.-C. (1,2), Temel, O. (2), Dehant, V. (1,2), Daerden, F. (3),Thomas, I. (3), Ristic, B. (3), Patel, M. (4), Bellucci, G. (5) , López Moreno, J. J. (6), and Vandaele, A. C (3)

(1) Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium, (2) Royal Observatory of Belgium (ROB),Brussels, Belgium, (3) Royal Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium (4) Open University (OU),Milton Keynes, the UK (5) Istituto Nazionale di Astrofisica (INAF-IAPS), Rome, Italy (6) Instituto de Astrofísica de Andalucía(IAA-CSIC), Granada, Spain

Introduction and background Methodology

Result and discussion Conclusion

Introduction and background

Seasonal and interannual variability of the CO2 and H2O ices onthe Martian surface is important for the understanding of Mars’current atmospheric dynamics and its variability.

Understanding the process of ice sublimation and condensationon Mars has implications on both short and long term climatechanges. Indeed, CO2 and H2O cycles play a major role in thecurrent Martian climate.

In addition, changes in polar cap variations have implications onthe rotation of the planet through atmospheric angularmomentum variations [1].

Objective: Better understand seasonal and interannual changes in the atmosphere and icecaps from H2O (almost permanent icecaps)and CO2 (icecaps very much changing) surface deposit evolutions on the Martian surface as a function of the seasons and years.

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Figure 1: Nadir view of the Martian South Pole, image using MGS/MOLA and MGS/MOC data [2].

Methodology

This project takes advantage of the NOMAD spectrometer nadir observations (LNO), on board the 2016 ExoMars Trace Gas Orbiter, to study the surface ice deposit evolutions on Mars.

The Nadir and Occultation for Mars Discovery (NOMAD) [3]:• One of the four instruments on board ExoMars Trace Gas Orbiter• Suite of three spectrometers designed to observe the atmosphere and the surface of Mars (SO, LNO, UVIS)

The Limb Nadir and solar Occultation channel (LNO channel):• Infrared spectrometer operating in the 2.3 – 3.8 µm range • Capable of doing nadir (1), solar occultation (3) and limb observations (2)

• LNO observations through different diffraction orders • Max 6 diffraction orders for one LNO observation

Surface ice deposits• Specific infrared signatures in the 2.3 – 3.8 µm range• Information on their composition (CO2/H2O ice), texture and grain size [4][5]

Detection• Definition of spectral indices based on spectral features similar to G. Bellucci et al., 2019 [6]• Combination of diffraction orders

Martian surface information

Figure 2: NOMAD observation geometry [3]

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Methodology

Ice Index:• Definition of two spectral indices using two diffraction orders

one in the spectral continuum, free from gaseous absorption, and the other on the basis of a CO2/H2O ice absorption band

• Ratio between the two previous spectral indices to remove the atmospheric effects

𝑆𝐼 =𝐿𝑀𝑎𝑟𝑠

𝐿𝑆𝑢𝑛 ∗ 𝐴𝑀

𝐼𝑐𝑒 𝐼𝑛𝑑𝑒𝑥 =𝑆𝐼𝑂𝑟𝑑𝑒𝑟 1𝑆𝐼𝑂𝑟𝑑𝑒𝑟 2

𝐿𝑀𝑎𝑟𝑠: spectral radiance of Mars (W/m²/sr/cm-1)

𝐿𝑆𝑢𝑛: spectral irradiance of the Sun at 1AU (W/m²/sr/cm-1)

AM: Martian albedo derived from Thermal EmissionSpectrometer (TES) onboard Mars Global Surveyor (MGS) [7]

NOMAD LNO spectral range

Figure 3: SNICAR simulated spectra [8]

Selection of diffraction orders (different LNO observations, different surface coverage) • Continuum part

194 [2275–2293.2 nm]; 190 [2322.9–2341.5 nm]; 189 [2335.2–2353.8 nm]• On the basis of the 2.7 µm CO2/H2O ice absorption band

169 [2611.8–2632.7 nm]; 167 [2642.8–2663.9 nm]

2.7 µm

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Result and discussion

Nadir data analysis

• Ice indices defined as 𝑆𝐼190

𝑆𝐼169(update of G. Bellucci et al., 2019 [6]),

𝑆𝐼189

𝑆𝐼167(update of L. Ruiz Lozano et. al, 2019 [9]) and

𝑆𝐼194

𝑆𝐼167

• Data for MY34 (Ls: 150°- 360°) and MY35 (Ls: 0°- 210°)• Seasonal plot (Latitude - time) • Binning 1° x 1°• SZA < 80°

Seasonal map using three ice indices for better coverage in time and space

• Observation of the sublimation process for the southern polar cap for MY34 (Ls = 150°- 250°) and MY35 (Ls = 150°- 210°, with a better coverage after Ls = 190°)

• No detection of the northern polar cap due to the lack of observations for MY34 (Ls = 300° - 360°) but observation of the sublimation process for MY35 (Ls = 0° - 40°)

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Conclusion

NOMAD LNO can observe surface ices and the sublimation process of the two polar caps (MY34 and MY35).

The analysis is ongoing to define the optimal combination of indices considering uncertainties related to the sensitivity of the instrument (AOTF, calibration) as well as the observational constraints.

The investigation of the polar cap sublimation/condensation process and interannual variations will be done using also other datasets (additional observations, GCM, ...).

UVIS and LNO combination can give further insight on the dynamics of surface ice deposits.

AcknowledgementsThe NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). Thisproject acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by Spanish Ministry ofScience and Innovation (MCIU) and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/R005761/1, ST/P001262/1,ST/R001405/1 and ST/R001405/1 and Italian Space Agency through grant 2018-2-HH.0. This work was supported by the Belgian Fonds de la Recherche Scientifique – FNRS under grant number 30442502(ET_HOME). The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica deAndalucía (SEV-2017-0709). US investigators were supported by the National Aeronautics and Space Administration. Canadian investigators were supported by the Canadian Space Agency.

References[1] Karatekin et al., 2005, Adv. Space Res., 38(4),739-744.[2] Mars Roll, Scientific Visualization Studio by NASA. https://svs.gsfc.nasa.gov/3896[3] Vandaele, A.C., et al., 2018. NOMAD, an Integrated Suite of Three Spectrometers for the ExoMars Trace Gas Mission: Technical Description, Science Objectives and Expected Performance. Space Sci Rev 214(80). https://doi.org/10.1007/s11214-018-0517-2 [4] Langevin et al., 2007. Observations of the south seasonal cap of Mars during recession in 2004–2006 by the OMEGA visible/near-infrared imaging spectrometer on board Mars Express. Journal of Geophysical Research: Planets, 112(E8), DOI: 10.1029/2006JE002816.[5] Pelkey, S.M., et al., 2007. CRISM multispectral summary products: Parameterizing mineral diversity on Mars from reflectance. Journal of Geophysical Research: Planets, 112(E8), DOI: 10.1029/2006JE002831.[6] Bellucci, G., et al., 2019. TGO/NOMAD Nadir observations during the 2018 global dust storm event, EPSC Abstracts, Vol. 13, EPSC-DPS2019-552-1. [7] Mars Global Data Sets, http://mars.asu.edu/data/tes_albedo/[8] The Snow, Ice, and Aerosol Radiative Model (SNICAR). https://github.com/mflanner/SNICARv3[9] Ruiz Lozano, L., et al., 2019. Use of NOMAD Observations (Trace Gas Orbiter) for Mars surface depositions, EPSC Abstracts, Vol. 13, EPSC-DPS2019-1781-1. Luca Ruiz Lozano

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https://svs.gsfc.nasa.gov/3896http://mars.asu.edu/data/tes_albedo/https://github.com/mflanner/SNICARv3