Subject: 25-121 Satellite observation of aquatic ecosystems using innovative hyperspectral technology

The study of coastal and inland waters is of considerable importance on a global scale given that nearly 40% of the world's population is located less than 100 km from the coast and 90% less than 10 km from inland waters. These highly dynamic ecosystems have a significant influence on productivity, the carbon cycle but also on society and the economy (e.g., flooding, pollution). In addition, access to drinking water is already and will become a critical problem in many parts of the world. The current and future needs to deepen their study are multiple: (i) better understanding of the functioning of these ecosystems, (ii) prediction of their evolutionary dynamics, particularly in the context of global changes, (iii) definition of strategies for mitigation of the risks of their degradation. There is then a significant interest in developing flexible and versatile satellite sensors dedicated exclusively to the optimal observation of these aquatic ecosystems on a global scale.

In this context, a future innovative satellite space mission from both a scientific and technological point of view (GALENE-Global Assessment of Limnological, Estuarine and Neritic Ecosystems project, Coordinator: M. Chami) is proposed to the European Space Agency (ESA) by an international scientific consortium of 50 experts from 13 countries in partnership with the company Thales Alenia Space (Cannes, France). The GALENE mission, which consists of a synergy of 3 instruments: a hyperspectral camera, a panchromatic camera and a multidirectional polarimeter, has the following scientific objectives: (i) observation of the properties and dynamics of coastal aquatic ecosystems and inland waters (e.g., lakes), (ii) the study of the carbon cycle, (iii) the spatio-temporal characterization of biodiversity and the assessment of water quality, (iv) the study of the impact of natural and societal processes, (v) the contribution to a better definition of the sustainable management of water resources and to the Sustainable Development Goals (SDG) of the United Nations Organization (UNO).

The innovative features and added values of a GALENE-type mission can be summarized as follows:

a) multi-angular polarimetric measurements will make it possible to discriminate mineral materials from biogenic materials and to characterize the directional properties of the observed aquatic surface,

b) for the first time in the history of water color, nocturnal observations will make it possible to characterize the dynamics of highly turbid zones such as river discharges and to a lesser extent, to detect major bioluminescence phenomena,

c) hyperspectral observations at a spatial resolution of 30 m with an unprecedented high radiometric performance (Signal-to-Noise Ratio greater than 500 in the visible bands) will make it possible to observe both turbid and dark aquatic scenes, the latter representing the majority of in inland waters, to evaluate the composition of benthic habitats and to identify phytoplankton groups in the water column.

 

Objective of the thesis and work plan

The objective of the thesis is to increase the technical maturity of one of the components of the GALENE-type concept, as recommended by ESA, namely the hyperspectral sensor, to enable its integration into a future satellite mission dedicated to the observation of aquatic ecosystems. The main challenges rely both on the development and on scaling of new optical instrument technologies, and on the implementation of advanced methods for calibrating the envisioned hyperspectral satellite data. The work plan includes two main areas. First, the hyperspectral optical instrument will be scaled and optimized by considering the latest advancements in the associated technologies. Second, innovative calibration strategies of the hyperspectral sensor will be proposed and evaluated. The activities of each phase of the works that will be performed during the PhD are as follows.

1) Phase #1: characterization of the hyperspectral sensor

a) evaluation of the performance of a hyperspectral acquisition system designed by Thales Alenia Space Cannes (e.g., stray light quantification and correction strategy, inter-band disturbance, radiometric and spectral performances) and optimization of its operating point

b) definition of performance stability and evaluation of the calibration needs,

c) evaluation of the relevance of the algorithms existing in the literature for retrieving aquatic products (e.g., phytoplankton group, benthic composition) from satellite hyperspectral radiances based on the operating point of the hyperspectral system studied.

 

2) Phase #2: calibration of hyperspectral satellite data

On the basis of the instrument defined during the phase #1 of the PhD, calibration strategies of the hyperspectral data will be investigated based on the performance requirements established for optimized observations of aquatic ecosystems. The following calibration capabilities will be examined (in order of priority):

a) on-ground pre-launch calibration of the hyperspectral payload,

b) in-flight (i.e., on-orbit) vicarious calibration using specific areas of interest on Earth (e.g., oligotrophic open ocean waters),

c) on-board calibration method based on devices that could be integrated into the payload.

 

PhD outcomes

The studies performed during the PhD imply forward-looking topics that will provide the french industry involved in the space field with innovative technologies for observing coastal and inland waters with currently unmatched technical performances. A further selection of a GALENE-like mission by ESA will imply significant benefits from both a socio-economical point of view by creating and secure hundreds of jobs within french and international companies and an environmental point of view with respect to the global carbon cycle knowledge, water pollution, biodiversity, protection of resources and drinkable water management.

 

Education background of the applicant and searched skills

- Engineer in Aerospace or instrumental optics

- Master in physics, instrumentation, sensors

- Skills on a scientific computing language (Python, Matlab, Scilab or other).

- Ease of integration into a team

 

Particular observations

The work will take place within the framework of the Côte d'Azur Space Observation Laboratory (LOSCA) which is a partnership between Thales Alenia Space company (Cannes, France) and the Côte d'Azur Observatory (Nice). The PhD student will be based in the building of Thales Alenia Space (Cannes, France).

The thesis will be supervised by Frédéric Pistone (Thales Alenia Space) and Malik Chami (Professor at the Lagrange Laboratory of the Côte d’Azur Observatory).

 

Scheduled beginning of the thesis: Fall 2025

 

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For more Information about the topics and the co-financial partner (found by the lab !); 

The applications need to be sent (CV + cover letter) to Malik Chami : malik.chami@upmc.fr and Frédéric Pistone : frederic.pistone@thalesaleniaspace.com.

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 14th, 2025 Midnight Paris time !

Engineer in Aerospace or instrumental optics  - Master in physics, instrumentation, sensors 

LAGRANGE