11:30 AM - 11:45 AM
[MIS02-04] A refractive index model of volcanic ash derived from satellite infrared sounder measurements for applications of HIMAWARI-8 retrieval algorithm
Keywords:volcanic ash, refractive index, Himawari-8
Japan Meteorological Agency (JMA) has been developing a retrieval system to provide volcanic ash products from HIMAWARI-8 infrared measurements through a volcanic ash detection/evaluation algorithm. For the estimation of ash cloud parameters, i.e. cloud top height, optical depth, particle size, and associated mass loading, accurate radiative transfer calculations in the modeled atmosphere are important. Because optical properties of the ash clouds strongly depend on the ash refractive index, a dataset of spectral refractive index in the infrared region for various types of volcanic ash materials is desirable. The current models of refractive index for volcanic ash, which were published more than thirty years ago, are insufficient in spectral resolution as well as in the number of alternatives for the use of multi-channel satellite remote sensing.
As reported in the literatures, refractive index of volcanic rocks and/or ash materials at infrared wavelengths had been estimated in laboratory from the spectral reflectance for the applied infrared light. The situation of satellite infrared sounder measurements for volcanic ash clouds in the atmosphere over land/ocean is essentially similar to the laboratory measurements. It suggests that the ash refractive index can be estimated from the infrared spectroscopy by satellites in condition of no ice/water clouds contamination and if the other unknown parameters, i.e. the ash cloud parameters, the atmospheric profile, and surface temperature/emissivity, are determined in advance or derived simultaneously. The estimated refractive index of the ash material by satellite infrared sounder has a potential to improve volcanic ash retrieval by HIMAWARI-8 for the same ash clouds and also for the ash clouds erupted from the same type of volcanos. In this work, a refractive index model, which derived from the measurements of infrared sounders, AIRS and IASI, for some volcanic events is proposed.
As reported in the literatures, refractive index of volcanic rocks and/or ash materials at infrared wavelengths had been estimated in laboratory from the spectral reflectance for the applied infrared light. The situation of satellite infrared sounder measurements for volcanic ash clouds in the atmosphere over land/ocean is essentially similar to the laboratory measurements. It suggests that the ash refractive index can be estimated from the infrared spectroscopy by satellites in condition of no ice/water clouds contamination and if the other unknown parameters, i.e. the ash cloud parameters, the atmospheric profile, and surface temperature/emissivity, are determined in advance or derived simultaneously. The estimated refractive index of the ash material by satellite infrared sounder has a potential to improve volcanic ash retrieval by HIMAWARI-8 for the same ash clouds and also for the ash clouds erupted from the same type of volcanos. In this work, a refractive index model, which derived from the measurements of infrared sounders, AIRS and IASI, for some volcanic events is proposed.