Supporting detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation

Significance Statement

Explosive volcanic eruptions generate huge amounts of ash clouds, inject an avalanche of aerosols, gases and ash into the troposphere, and can even reach into the stratosphere. Major eruptions can cause short-time climate change in case sulfur dioxide is emitted to the atmosphere forming sulfate aerosols with extensive residence times of approximately 1 to 3 years. The impact however depends on the location of the volcano, total mass erupted, the extent of the dispersion due to atmospheric circulation, and the altitude reached by the ash and sulfur dioxide.

Ash clouds pose a threat to aviation considering that they can damage aircraft engines even far away from the eruptions. Therefore, research attention has centered on the enhancement of detection as well as monitoring of volcanic ash clouds. However, observing the density of the ash clouds as a function of height becomes a major challenge considering that values more than 2 mg/m3 could be rendered dangerous for aircraft engines. Previously, this parameter could only be detected by flying into the clouds with all the relevant risks until recently when infrared spectral imaging indicated promising results.

A good understanding of the cloud top altitude is important in order to offer information on ash-free altitude regions for air traffic as well as on potential overshooting and sulfur dioxide spread into the atmosphere. However, the discrimination of ash clouds from other forms of clouds can be challenging. Researchers at the Wegener Center of the University of Graz in Austria, Riccardo Biondi, Andrea Steiner, Gottfried Kirchengast, and Therese Rieckh, in collaboration with Hugues Brenot at the Belgian Institute for Space Aeronomy studied the potential capacity of the radio occultation method for supporting volcanic cloud monitoring and detection. The research team used geographically co-located Global Navigation Satellite System radio occultation profiles in order to detect the top altitude of volcanic clouds and to assess their effect in terms of temperature change signatures. Their research work is published in Advances in Space Research.

The authors adopted, at the first step, radiometric imaging observations in the thermal infrared as well as UV-visible for detecting volcanic ash as well as sulfur dioxide clouds and for isolating against water clouds. In the second step, the authors adopted geographically co-located profile observations from radio occultation for identifying the cloud top altitude and assessing the thermodynamic effect of volcanic clouds.

In their pioneering demonstration study, the researchers used approximately 1300 radio occultation profiles co-located with two eruptions in 2011 (Puyehue and Nabro) and realized that an anomaly method they developed recently for identifying convective cloud tops and analyzing the vertical thermal structure of deep convective systems could be applied for volcanic clouds. “Assessing the atmospheric thermal structure after volcanic eruptions, we found clear cooling signatures induced by volcanic ash cloud tops in the troposphere for the Puyehue case,” says Andrea Steiner, corresponding author from the University of Graz, and her senior author colleague Gottfried Kirchengast adds “Another exciting finding is that for the Nabro case we detected a considerable warming in the stratosphere over several months, implying that we could see the sulfate cloud’s local warming effect.”

The outcomes of their study are impressive for future large-scale implementation of radio occultation data for supporting the detection and monitoring of volcanic clouds as well as their effects on weather and climate.

detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation-Advances in Engineering

About The Author

Riccardo Biondi holds a master’s degree in electronic engineering from University of Perugia, Italy and a PhD degree in atmospheric physics from the Danish Technical University (DTU) Copenhagen, Denmark. He defines himself a “freelance researcher” and during his career he worked for the University of Perugia, the European Space Agency (ESA), the Abdus Salam International Centre for Theoretical Physics (ICTP), the Wegener Center for Climate and Global Change, the National Research Council of Italy (CNR), and he was visiting scientist at the US National Center for Atmospheric Research (NCAR). He was Management Committee Member of the COST Actions GNSS4SWEC and TOPROF.

His research activity was recognized and granted with a Marie Curie fellowship (2013-2015) and an AXA Research Fund fellowship (2015-2017). His main research interest is in extreme atmospheric events such as deep convection and volcanic eruptions, topics in which he also leads an international school.

About The Author

Andrea K. Steiner holds a PhD degree in meteorology and geophysics from the University of Graz, Austria. She studied in Biosphere 2, AZ, USA, and was visiting scientist at the Danish Meteorological Institute (DMI), Copenhagen, Denmark, University Corporation for Atmospheric Research (UCAR) and the National Center for Atmospheric Research (NCAR), Boulder, CO, USA. Lecturing since 2003 at the University of Graz, she obtained in 2013 the venia docendi in geophysics and environmental system sciences and was appointed tenured professor in 2017.

She is Vice Director of the Wegener Center for Climate and Global Change at the University of Graz and Vice Head of its Atmospheric Remote Sensing and Climate System (ARSCliSys) Research Group. Her research in atmospheric and environmental physics focuses on atmospheric remote sensing and use for climate change monitoring and research. She is an expert on radio occultation and its application for atmosphere and climate.

About The Author

Gottfried Kirchengast studied physics, geophysics and meteorology at the University of Graz, Austria, receiving 1992 his natural sciences PhD. Building on a tenure-track assistant professorship and many research stays abroad, together with obtaining prestigious research awards and major international project leads, he is since 2003 professor of geophysics (Alfred Wegener’s Chair) and since 2005 director of the Wegener Center for Climate and Global Change at the University of Graz. He is also honorary professor at the National Space Science Center of the Chinese Academy of Sciences, adjunct professor at the Royal Melbourne Institute of Technology (Australia), and member of the Austrian Academy of Sciences. He is author or co-author of more than 300 scientific publications, adviser of more than 40 PhD students, and repeatedly made and continues to make pioneering research and international and national leadership contributions in the fields of Earth observation and climate science.

About The Author

Hugues Brenot has a background in Geodynamics (Postgraduate Degree about the implementation of reological model of Mars planet at EOST/University of Strasbourg, 2002), in Geodesy and GNSS meteorology (PhD at the University of Grenoble IsTerre/OSUG and Météo-France/CNRM Toulouse, 2006). Involved in GALOCAD/ESA project (2006-2008) at IRM-KMI, he is developing since 2010 the monitoring of volcanic plumes using remote sensing at BIRA-IASB (

His research still focuses on the detection of tropospheric/ionospheric signatures in the GNSS signals; work achieved in the frame of the Solar-Terrestrial Centre of Excellence (STCE) and the GNSS4SWEC COST Action. Recently, he has been involved in the detection of SO2 emission from Nyiragongo volcano, North Kivu ( using ground based UV camera and DOAS-spectroscopy.

More information about DOAS team:

About The Author

Therese Rieckh completed her master’s degree in physics in 2013 from the University of Graz, Austria. As a member of the research group ARSCliSys at the Wegener Center for Climate and Global Change, she studied the global tropopause using GPS radio occultation. In collaboration with the Wegener Center at the University of Graz, she has spent the past three years as a visiting scientist at the University Corporation for Atmospheric Research (UCAR) in the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Program in Boulder, CO, USA, where she is working on her PhD studying the value of radio occultation for observing tropospheric water vapor.


Riccardo Biondi, Andrea K. Steiner, Gottfried Kirchengast, Hugues Brenot, Therese Rieckh. Supporting the detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation. Advances in Space Research, Available online 28 June 2017.

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