| Abstract: |
Volcanic ejections during an eruption can be divided into gas and solid emissions. The latter are made by mineral fragments with size from micrometers to several centimeters, generally referred as tephra. Tephra can be schematically distinguished into very fine ash, fine ash, coarse ash, lapilli and large lapilli. Both emissions represent one of the most impacting sources of natural pollution as well as a natural hazard for nearby communities and activities. In addition, the prediction of time-space dispersion of volcanic particle emissions is crucial for better assessing the solar-Earth energy budget in the climatic trend as well as for ensuring an enhanced safety standard for flight routing.
Satellite observation of near-source volcanic plumes and distal ash clouds at a global scale is typically carried out by exploiting mainly thermal infrared (TIR) radiometric sensor imaging both from low-Earth-orbit (LEO) and geosynchronous Earth orbit (GEO) platforms. Techniques based on two-channel TIR brightness temperature difference (BTD) are used for quantitative detection and estimates of the tephra mass loading. However, there are evidences that BTD techniques cannot be applied to particle size larger than about 20 microns due to saturation effects, unless exploiting fluid dynamics plume models. In this respect, space-borne microwave (MW) and millimeter-wave (MMW) radiometers can be complementary observation techniques since microwave and millimeter-wave radiation is sensitive to larger particles and hardly saturate since the optical extinction is significantly lower than in the TIR. The drawback is the spatial resolution, which is about 10 times larger for MW than TIR, reducing the capability of plume detection due to beam filling problems. Moreover, the temporal sampling of the acquisitions performed in the MW spectrum can be sensibly lower than that obtained when considering TIR sensors because of a reduced coverage of the former with respect of the latter.
The recent Calbuco volcanic subPlinian eruption in Southern Chile is an excellent case study where previously mentioned issues can be explored due to the large number of available spaceborne measurements. The 2015 Calbuco eruption was observed by the cross-track scanning Visible Infrared Imaging Radiometer Suite (VIIRS) and the Advanced Technology Microwave Sounder (ATMS), both of them on board the LEO Suomi National Polar-orbiting Partnership (S-NPP) platform. Moreover, it was observed by the Moderate-resolution Imaging Spectroradiometer (MODIS), on board Terra and Aqua satellites and the visible (VIS) and near-infrared (NIR) Lidar aboard the LEO-based Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), part of the so called A-Train.
The above list of active and passive satellite instruments provides an unprecedented picture of the Calbuco subPlinian eruption ranging from visible-infrared (0.512 – 12.013 microns) to microwave (23.8 – 183.31 GHz) spectra. The goal of this work is to show quantitatively: i) how satellite MW radiometric measurements can complement satellite TIR measurements for the detection and estimation of near-source volcanic plume parameters; ii) how TIR-based volcanic products, derived from different sensors and algorithms, can provide a physically-consistent characterization of distal ash clouds and can be coupled with LEO spaceborne lidar retrievals, properly tuned for volcanic ash particles; iii) how satellite-based products of near-source tephra plume and distal ash cloud mass loading are in a fairly good agreement with available ground-based sampling of volcanic deposits due to the 2015 Calbuco eruption.
The presentation will illustrate the 2015 subPlinian Calbuco eruption and the considered satellite datasets in the MW, TIR and VIS-NIR ranges. It will introduce and apply the tephra ATMS MW detection and parametric retrieval of near-source parameters showing the useful complementary information given by VIIRS and including the VIS-TIR ash retrieval intercomparison for the distal ash cloud. |
