Volcanologists require robust gas sensors for field measurements, yet commercial devices falter under volcanic extremes—corrosion, pressure, vibration, and high humidity disrupt readings and damage equipment. To address this, CEA-Leti leveraged its background in toxic and greenhouse gas sensors, originally developed for environmental monitoring, and partnered with the Laboratoire Magmas et Volcans (LMV) at the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC). The result is the MUGS (MUltiGas Sensor) project, funded by the French National Research Agency via CEA-Leti’s Carnot Label. Its goal: a mug-sized, drone-mountable multisensor that withstands harsh volcanic terrain and measures gases directly in plumes.

The sensor uses photoacoustic spectroscopy. Miniaturization was a central challenge, solved with CEA-Leti’s silicon manufacturing expertise: the photoacoustic cell is just millimeters across, with integrated microphones that detect sound generated by gas absorption. Eventually, all components will be embedded in a single silicon chip; currently, modular electronics handle signal collection and control. Four quantum cascade lasers target the mid‑infrared (4–7 µm) region, matching the absorption bands of CO₂, CH₄, N₂O, CO, H₂O, plus volcanologically critical SO₂ and H₂S. The device operates on contact with air and needs only a tiny gas volume.

After months of lab calibration, the sensor was tested at La Soufrière volcano in Guadeloupe (December 4–12, 2025). It performed stably and repeatably in tough conditions. Comparison with volcanologists’ instruments showed convincing agreement on SO₂ and H₂S; notably, the MUGS sensor also measured CH₄, which existing equipment could not detect. The sensor operated near the summit crater, its case interior enabling leak detection with the second‑generation photoacoustic design.

Future work, supported by the European GENESIS and MILADO projects, aims to enable long-term fixed monitoring and drone‑based concentration mapping, transmitting data remotely.

Understanding and predicting volcanic activity is a complex undertaking. Volcanologists must collect and evaluate a wide range of data, such as magnetic and seismological data, and gas readings.

Volcanologists therefore use gas sensors when taking field measurements. Unfortunately, devices that are currently on the market are not intended for use in extreme volcanic conditions. Corrosion, pressure, vibrations, and high relative humidity can all disrupt measurements and damage equipment.

However, CEA-Leti has expertise in designing and manufacturing gas sensors, which were originally developed to measure toxic gases or low-level greenhouse gases. The application to volcanology was consequently an interesting option to explore for monetizing the technology. The MUGS (MUltiGas Sensor) project arose following conversations with the Laboratoire Magmas et Volcans (LMV, Laboratory of Magma and Volcanoes) at the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC, Clermont-Ferrand Earth Physics Observatory). It aims to develop a miniature (the size of a mug) portable multigas sensor capable of resisting the extreme conditions of volcanic land and of being embedded on a drone, to safely investigate volcanic plumes. The project is funded by the Agence Nationale de la Recherche (ANR, French National Research Agency), by way of CEA-Leti's Carnot Label of Excellence.

The multigas sensor relies on the principles of photoacoustic spectroscopy detection.

Although the research team was already proficient in the field, the MUGS project required overcoming several challenges, such as miniaturization. Thanks to CEA-Leti's expertise in silicon manufacturing, the scientists were able to design a photoacoustic cell measuring just a few millimeters which integrates microphones that can measure sound that is produced. Relying on silicon will ultimately have the advantage of embedding everything into a single component. Currently, signal collection and control rely on modular electronics made up of interconnected boards that were developed at CEA-Leti.

Finally, the assembly features four quantum cascade lasers. These make it possible to ​cover mid-infrared wavelengths, particularly in the 4 to 7 µm band, which is adapted to the targeted gases.

The MUGS project has therefore resulted in creating a compact, multigas sensor that can measure ​greenhouse gases: CO2, CH4, N2O, CO and H2O, along with two gases that are of particular interest to volcanologists: SO2and H2S. What is more, the device functions upon contact with air, and only requires a small volume of gas to take measurements.

Following several months of laboratory calibrations, the sensor was tested at La Soufrière volcano, Guadeloupe, last December 4th to 12th, 2025. This step demonstrated that the device works in a stable and repeatable​ way in difficult environmental conditions. Collected data was then processed and compared with measurements taken by the volcanologists. This yielded convincing results on SO2and H2S, two of the three targeted gases. However the volcanologists' devices were unable to measure the third one, CH4. The MUGS sensor, whereas, performed this task successfully.

Researchers now wish to improve the device in​ order to take and transmit measurements when it is installed on a fixed location for several months at a time, or from a flying drone, to map concentrations. These prospects are being researched thanks to European funding for theGENESISandMILADO​ projects.

​Both sensors are operating in the area of the crater near the summit​​​​​

The interior of the case allows for the detection of gas leaks using ​​​th​e second-generation multi-gas sensor based on the photoacoustic principle.​​​​