Jean-Philippe Combe

Professional History

Birth: 10 km from Juvinas, France, where the fall of a meteorite was witnessed on June 15, 1821.   Childhood: In the Ardèche département, where the first human flight by Étienne Montgolfier took place in a hot air balloon, la Montgolfière, on September 19, 1783.   First interest in space science: At the age of 8 from a book called Le Petit Livre du Ciel (The Small Book of the Sky), again at the age of 11 from a book called Le Grand Livre du Ciel (The Big Book of the Sky), and from looking at the rings of Saturn through a 75 mm telescope on equatorial mount at the age of 13.   General university studies diploma: Science of matter, specialty in physics in Valence, France.   Bsc in Physics and Physics applied to Geophysics in Grenoble, France, including an internship under the supervision of Dr. David Mouillet for the evaluation of a Performance Estimator software for the Nasmyth Adaptive Optics System (NAOS) of the Near-Infrared Imager and Spectrograph (CONICA) on the Very Large Telescope (VLT) of the European Southern Observatory in Paranal, Chile.   MSc in Science of the Earth and the Environment, speciality in terrestrial and planetary sciences in Toulouse, France, including an internship under the supervision of Claude d'Uston and Serge Chevrel on mapping the elemental composition of the Aristarchus Plateau with the Gamma-Ray Spectrometer of the Lunar Prospector space mission.   PhD thesis entitled "Studies of planetary surfaces by hyperspectral visible infrared remote sensing" at the Laboratory of Planetology and Geophysics of Nantes (now Laboratory of Planetology and Geosciences), France, under the supervision of Pr. Christophe Sotin, Pr. Patrick Launeau and Dr. Daniela Despan. At the time (at the turn of the millennium), the objective of this thesis was to get ready for the analysis of (then future) data from imaging spectrometers onboard the Mars Express and Cassini missions. Three separate studies eventually constituted this thesis.   - First, the LPGN acquired hyperspectral airborne data of a portion of the western shore of France near Nantes, over the Bourgneuf bay) with the Digital Airborne Imaging Spectrometer DAIS 7915, in collaboration with biologists Laurent Barillé and Vona Melder from the nearby institute ISOmer Nantes. The objective was to map the biomass of microphytobenthos (benthic microalgae). Ground calibration was obtained by in-situ measurements with a portable point spectrometer, as well as sampling and laboratory measurements of the biomass. Spectral analysis was done by by adapting the Modified Gaussian Model (MGM, Sunshine et al., 1990) that was designed to fit the absorption bands absorptions in spectra of mafic minerals such as pyroxenes and olivines. These bands are due to ligand-to-metal electronic charge transfer absorptions, and they result in Gaussian as a function of wavelengths. MGM was relevant to this study (Combe et al., 2005) because in photosynthetic systems, light absorption by chlorophyll induces electron transfer (Berg et al., 2002).   - Second, the LPGN acquired an hyperspectral airborne data of the Oman ophiolite complex with the HySpex imaging spectrometer, in order to map the mineral composition of the altered rock surface and infer on the nature and composition of the rocks. The MGM was used mostly to remove the continuum for the minimization of photometric effects, and spectral indices were developed to characterize the narrow bands of alteration in the near-infrared (Combe et al., 2006).   - Third, Mars Express and Cassini were inserted in orbit at their respective destinations only a few months apart, and the LPGN received data from the two respective imaging spectrometers Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) and the Visual and Infared Mapping Spectrometer (VIMS). Both datasets required exploring and optimizing the instrument calibration before starting to interpret the data. For the thesis, the focus was to improve the technique of spectral mixture analysis (SMA) by developing a tool that was later named Multiple-Endmember Linear Spectral Unmixing Model (MELSUM, Combe et al., 2008), based on linear unmixing for mineral identification and mapping of the surface of Mars with OMEGA/Mars Express. For validation, MELSUM results were tested on AVIRIS data of the Cuprite mining site in Arizona and compared with spectral classification and mapping obtained with the expert system Tetracorder (Clark et al., 2003).   Before the defense of this thesis, Pr. Tom McCord, in visit to LPGN, was looking for a new scientist at the Bear Fight Center (later the Bear Fight Institute or BFI) in Winthrop, WA, United States.   Three-week visit at the BFI to work on the calibration of the High-Resolution Stereo Camera (HRSC) on Mars Express and mapping of H2O ice.   PhD thesis defense in Nantes three weeks after coming back from Winthrop.   Research Scientist at the Bear Fight Institute (2006 - 2021).   Senior Scientist at the Planetary Science Institute (2021 - present)   To be continued.   Please be patient.