Poster de conférence
Résumé : Large fire events are known to inject important amounts of pollutants into the atmosphere. Those pollutants are concentrated in plumes and can be transported far from the fire source, especially when the injection is directly into the free troposphere. The knowledge of fire injection height, which is important for atmospheric chemistry models and dispersion models, is often inaccurate. In this work we explore the possibility to obtain information about the altitude of fire plumes, using IASI radiances, and in particular the information they carry on the carbon monoxide (CO) vertical profile and the ethylene (C2H4) total column. For CO it is well known that IASI allows retrieving a weakly resolved profile in most situations with, in the best cases, about two independent pieces of information. The retrieval of CO profiles is achieved operationally and globally with the FORLI software, which relies on the Optimal Estimation method. The use in FORLI of an a priori profile representative of background conditions, and of an associated covariance matrix with significant correlation between vertical levels, results in generally smoothed retrieved CO profiles, without a pronounced maximum. We will show that the use of an alternative choice of a priori constrain (with less correlation) allows capturing local enhancements in CO over a narrow range of altitudes, which can then be assigned to a plume altitude. A series of well-documented fire events, with varying injection heights, will be discussed to evaluate the reliability of the method; the validation will be performed mainly with measurements from CALIPSO. In addition to CO, we will show that C2H4 measurements from IASI can be used as a robust indicator of fire plumes injected above the boundary layer. This is based on the fact that the sensitivity of IASI to boundary layer C2H4 is generally too low to produce a detectable signal in the radiances, while the opposite prevails when C2H4 is found at higher altitude. The availability of a decadal set of C2H4 from IASI allows to verify this on a very large set of situations. We will discuss the results mainly by correlating the C2H4 columns from IASI to injection heights from the Global Fire Assimilation System (GFAS), which operationally assimilates Fire Radiative Power from different satellite sensors.