[LUM#16] Before us, the flood

[LUM Magazine] - Published on October 31, 2022 in Science-Society

Since they can't be predicted, every year or so, the heavy rains that hit the Mediterranean region cause serious damage to people and property. An ambitious plan involving a nanosatellite, a ferry, and a few smart people could change all that by 2023.

October 15, 2018: torrential rain falls overnight in the Aude region. The toll is heavy: 13 dead (France Bleu Occitanie). In 2015, 20 people lost their lives in Mandelieu-la-Napoule, including a dozen trapped in their cars by the sudden rise in water levels (France Bleu Azur). How can we explain the occurrence of such violent and sudden storms? They are caused by a conflict between warm, humid air masses from the sea and cold air at high altitude coming from the Cévennes, hence their name: Cévenol episodes.

"By detecting these masses of warm air as soon as they form over the sea and using a very fast data transmission chain, we could better anticipate these episodes and better protect populations," explains Laurent Dusseau*. And to accomplish this mission, the director of the Montpellier University Space Center (CSUM) already has his champion! Robusta 3A Méditerranée, a 30 cm high nanosatellite, entirely designed by the CSUM with the help of more than 150 students, apprentices, and interns since 2013 and the support of the Van Allen Foundation, a partner foundation of the University of Montpellier.

Mobile sensors

Detecting humid air masses is nothing new. Météo-France, a partner in the project, already has sensors that use signals emitted by our phones' satellite navigation systems (GNSS). "The presence of water in the atmosphere modifies these signals and makes it possible to calculate the amount of vapor at a given location," explains Laurent Dusseau. There are more than 800 humidity sensors on French soil. On land, but not at sea, where the air masses that cause Cévenol episodes form.

To collect this data offshore, researchers will take one of these sensors aboard a ferry crisscrossing the Mediterranean from Sète. It's a simple idea for a major technological challenge being tackled by the École Nationale Supérieure de Techniques Avancées (ENSTA Bretagne) and the Institut National de l'Information Géographique et Forestière (IGN), both of which are involved in the venture. "The fact that the sensor is mobile involves many more variables, such as wave and boat movements," explains Laurent Dusseau. "A thesis is currently being written at ENSTA on this issue."

Data freshness

Second technological challenge: data speed and freshness. "For the information captured by Robusta to be valid, we will have to demonstrate that we can process it and send it back to end users within an hour, an hour and a half at most. " The end users? Météo-France, of course, but also the Hérault departmental fire and rescue service (Sdis 34), which joined the project last fall.

Robusta 3A, meanwhile, continues to prepare for its big flight : "The prototype has passed the critical design review, which means that the entire satellite design has been validated. We are now in the testing phase." Scheduled for the end of 2022, the launch of the nanosatellite will mark the beginning of a journey that will see it fly over the Mediterranean twice a day for a year. And what next? "In space, you have to be humble. We'll see how Robusta 3A performs and, if it does well, then yes, we'll continue the experiment, " concludes Laurent Dusseau.

*IES (UM -CNRS)

Keywords: LUM#16, Research, Science, Company, Technology