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Study of Martian Dust Aerosol with Mars Science Laboratory Rover Engineering Cameras

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Study of Martian Dust Aerosol with Mars Science Laboratory Rover Engineering Cameras UNIVERSIDAD DEL PAÍS VASCO – EUSKAL HERRIKO UNIBERTSITATEA (UPV/EHU) STUDY OF MARTIAN DUST AEROSOL WITH MARS SCIENCE LABORATORY ROVER ENGINEERING CAMERAS Hao CHEN CHEN Supervisors: Prof Agustín SÁNCHEZ LAVEGA Dr Santiago PÉREZ HOYOS MAY 2019 (c)2019 HAO CHEN CHEN UNIVERSIDAD DEL PAÍS VASCO – EUSKAL HERRIKO UNIBERTSITATEA (UPV/EHU) Departamento de Física Aplicada I - Escuela de Ingeniería de Bilbao Grupo de Ciencias Planetarias STUDY OF MARTIAN DUST AEROSOL WITH MARS SCIENCE LABORATORY ROVER ENGINEERING CAMERAS A dissertation submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy by Hao CHEN CHEN Supervisors: Prof Agustín SÁNCHEZ LAVEGA Dr Santiago PÉREZ HOYOS MAY 2019 I II Abstract Planetary atmospheres other than that of Earth provide natural laboratories to test our theories and models for climate studies and can help to identify the physical processes involved in the behaviour and evolution of a planet’s climate. Mars has always played a predominant role in comparative studies with Earth: the existing similarities allows to apply our terrestrial models, whereas the differences can provide us a better understanding of present atmospheric processes and characterise its past climate, in order to study why the two planets have followed different evolutionary paths, and even shedding light whether Mars could once have supported life. Extensive exploration efforts in the robotic exploration of Mars have retrieved large amount of data of Mars’ atmosphere. Dust aerosol is the main driver of Mars’ atmospheric variability, and the determination of the particles’ properties is of high relevance for estimating its climate forcing. In particular, the angular distribution of sky brightness can be evaluated to retrieve valuable information regarding the physical properties of the aerosol particles and atmospheric dust loading. In this study we show that images retrieved by the Mars Science Laboratory (MSL) engineering cameras (Navcam and Hazcam) can be used to constrain the size and shape of dust aerosol particles, and to derive the column dust optical depth. A radiative transfer based iterative retrieval method was implemented in order to determine the aerosol modelling parameters that best reproduce the sky radiance as a function of the scattering angle observed by MSL engineering cameras. Dust aerosol particles’ size were derived from measurements of the intensity decay within the solar aureole region (scattering angles < 30º), whereas the sky radiance at intermediate and large scattering angles were evaluated to derive the single scattering phase function. Particle’s shape was characterised then by comparing the retrieved phase functions with Double Henyey-Greenstein (DHG) analytical phase functions, T-matrix calculations of light scattering properties by randomly oriented non-spherical particles and experimental phase function retrievals of different Martian dust analogue samples. Dust size results show a seasonal behaviour with a positive correlation between dust column opacity and particle’s size, with effective radius reff ranging 0.75 to 2.00 μm. Best fitting DHG parameters generated a phase function with asymmetry parameter g ~ 0.65. Differences in the backscattering region were observed in the retrieved phase functions during the non-dusty season; however, no clear evidences of seasonal or interannual variability were detected. T- matrix results describe particles with diameter-to-length (D/L) ratios of 0.7 and 1.9 for cylinders, and D/L = 2.0 for spheroids (“disk shaped”); and the best fitting Martian dust analogue corresponded to the basalt sample. Results show an overall good agreement with previous studies and have contributed to extend the available observational data and to parameterise dust phase functions. The tools and procedures developed during this research can be implemented for the analysis of retrievals from future Mars exploration missions. Keywords: Martian atmosphere, dust aerosol, MSL engineering cameras, Navcam, Hazcam, radiative transfer. UNESCO codes: 2104.03, 2104.07, 2202.07, 2209.14, 2209.20, 2209.23, 2501.23 III IV Acknowledgements En las siguientes líneas quiero mostrar mi más sincero agradecimiento a las diferentes personas que me han apoyado a lo largo de estos años de doctorado. En primer lugar, a mis directores de tesis Santiago Pérez Hoyos y Agustín Sánchez Lavega. Gracias haberme dado la oportunidad de investigar y trabajar en el estudio de la atmósfera de Marte durante todo este tiempo. Vuestros útiles y sabios consejos han sido siempre una constante. Extiendo este agradecimiento a todas las personas del Grupo de Ciencias Planetarias. Gracias por haberme transmitido la pasión y dedicación que ponéis día a día en vuestra labor de investigación, además del excelente ambiente de compañerismos y colaboración. Muchísimas gracias también a Scot Rafkin, por recibirme y darme la fantástica oportunidad de realizar parte de mis tareas en Southwest Research Institute en Boulder, Colorado (USA). Ha sido todo un privilegio para mí el haber podido compartir este tiempo con todos vosotros. También quiero dar gracias a todas las personas del Departamento Física Aplicada I de la Escuela de Ingenieros de Bilbao. Gracias por haberme acogido como uno más. Del día a día en el departamento, tampoco podría olvidarme de toda la gente con los que he compartido despacho, cafés, congresos, comidas y debates de la más diversa y variada naturaleza durante este tiempo. Gracias Iñaki, Jon, Ander, Arrate, Macarena, Itsaso, Itziar, Naiara, Jorge, Peio, Aritz, Laura y Mateu. Quiero acordarme también de todas las personas que a lo largo de estos años me han ayudado y han hecho todo lo posible para que yo esté escribiendo estas líneas ahora mismo. Gracias de corazón. Por último, quiero expresar mi gratitud a mi familia y amigos, que siempre han estado ahí conmigo y nunca han dejado de apoyarme. Infinitas gracias. Hao CHEN CHEN, Donostia-San Sebastián, Mayo 2019 V VI Index Abstract ....................................................................................................................................... III Acknowledgements ..................................................................................................................... V Index ........................................................................................................................................... VII List of figures .............................................................................................................................. XI List of tables ............................................................................................................................. XIII Acronyms and abbreviations .................................................................................................. XV 1. INTRODUCTION ................................................................................................................. 17 1.1. Dust in the Martian atmosphere .................................................................................. 20 1.1.1. Timekeeping on Mars .......................................................................................... 20 1.1.2. The atmosphere of Mars ..................................................................................... 21 1.1.3. The dust cycle and its effects .............................................................................. 24 1.2. Atmospheric dust observations and missions ............................................................. 28 1.2.1. The Mars Science Laboratory mission ................................................................ 30 1.3. Research motivation .................................................................................................... 32 1.4. Aim and objectives ...................................................................................................... 32 1.4.1. Observational data review and image processing .............................................. 32 1.4.2. Radiative transfer model of Mars’ atmosphere ................................................... 33 1.4.3. Retrieval of atmospheric dust loading and aerosol particle properties ............... 33 1.4.4. Preparation of outcomes, procedures and tools for future studies ..................... 33 1.5. Structure of the thesis ................................................................................................. 33 2. RADIATIVE TRANSFER AND LIGHT SCATTERING ........................................................ 35 2.1. Radiative transfer in planetary atmospheres ............................................................... 36 2.1.1. Definitions and equation of radiative transfer ...................................................... 36 2.1.2. Separation of azimuthal dependence .................................................................. 38 VII 2.1.3. Discrete Ordinate Approximation: Matrix formulation .......................................... 39 2.1.4. Discrete Ordinate Approximation: Solution ......................................................... 42 2.2. Light scattering by aerosol particles ............................................................................ 48 2.3. Calculation of radiative properties ............................................................................... 50 2.3.1. Mie theory ............................................................................................................ 51 2.3.2. Rayleigh scattering .............................................................................................
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