Hans Liebe Lecture

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Title: "Microwave and Millimeter-wave Earth Surface Emissivity: Modeling Challenges for Surface and Atmospheric Characterization"

Satellite passive microwave observations are widely used to characterize both the Earth’s atmosphere (e.g., temperature and humidity profiles, precipitation) and its surface (e.g., ocean surface temperature and wind speed, soil moisture, and sea ice concentration). In atmospheric applications, the surface contribution can be a source of uncertainty, whereas in surface applications it provides the signal of interest. In both cases, however, proper interpretation of the measurements requires an accurate description of atmospheric radiative properties and surface emissivity.

This talk will focus on Earth’s microwave surface emissivity. With the increasing use of microwave and millimeter-wave observations from ~1 to ~700 GHz for meteorological and climate applications, a robust and consistent description of surface emission is needed across a wide range of environments, including the ocean, sea ice and snow, arid regions, and vegetated surfaces. Different approaches have been developed, ranging from physical models to satellite-derived emissivity atlases. We will discuss an emissivity parameterization that combines physical understanding with constraints from satellite observations, and examine challenges such as atmospheric absorption and emission, the surface emitting temperature, and potential subsurface contributions.

This perspective naturally connects surface emissivity modeling with the fundamental problem of atmospheric microwave absorption and propagation, highlighting the continuing relevance of the pioneering work of Dr. Hans Liebe and its importance for interpreting modern microwave and millimeter-wave satellite observations.

Dr. Prigent received her Ph.D. in Physics from the University of Paris, France, in 1988. Since 1990, she has been a Research Scientist with the Centre National de la Recherche Scientifique (CNRS), based at Paris Observatory. From 1995 to 2000, she was on leave from CNRS and worked at NASA’s Goddard Institute for Space Studies (GISS), Columbia University, New York. She is co-founder of Estellus, a Paris-based small company specializing in satellite Earth observation. Her research focuses on microwave remote sensing of the Earth’s surface and atmosphere, for global applications. Her work includes microwave radiative transfer modeling and parameterization (e.g., ocean and land surface emissivity), retrieval of key surface variables (e.g., ocean and land land surface temperature, surface water extent, sea ice concentration), and the development of millimeter-wave cloud products. She is involved in several satellite missions and instruments with ESA and EUMETSAT, including the MicroWave Imager (MWI) and Ice Cloud Imager (ICI) on board MetOp-SG and the Copernicus Imaging Microwave Radiometer (CIMR) mission.