Calcul des volumes des coulées de lave au Piton de la Fournaise par la méthodologie SfM

This presentation by Nicolas Villeneuve, a researcher at the Observatoire Volcanologique du Piton de la Fournaise, details the methodology and results of calculating lava flow volumes at Piton de la Fournaise using Structure-from-Motion (SfM) photogrammetry. The need for accurate volume measurements is emphasized for understanding volcanic dynamics and magma production. Traditional methods include estimating average thickness multiplied by area, comparing digital elevation models (DEMs), and using thermal satellite data. The team has developed expertise in using aerial photography from ULM and drones, but these methods are limited by coverage and weather. To overcome these limitations, they utilize satellite imagery from Pléiades in stereo and tri-stereo modes, processed with the MicMac and Formataire chains. They acquired 15 stereo/tri-stereo Pléiades images from 2013 to 2024, complemented by aerial DEMs and Copernicus data, allowing them to constrain 31 eruptions. Errors were assessed by comparing DEMs to GNSS ground control points, yielding absolute errors of 3.5-4 meters, but relative errors of about 1 meter when using a reference DEM. They derived a power-law relationship between flow area and volume, enabling estimation of volumes for five eruptions that were too small or obscured. Cumulative volumes since 2010 were calculated, showing that previous estimates were slightly overestimated. The operational protocol via Formataire ensures continuous monitoring and specific satellite tasking. The presentation concludes with a Q&A session addressing periodicity in eruption volumes, application to river and landslide monitoring, and challenges with lava flows entering the ocean.