Remote sensing of volcanic ash: Synergistic use of ash models and microwave observations of the erupting plumes

The goal of this work is to show potentials and drawbacks of Dual Polarization measurements of volcanic plume from microwave ground-based X-band radar (DPX). Measurements of brightness temperature (BT) from the space-orbiting microwave radiometer are used as well and compared with DPX retrievals of total columnar content (TCC). The latter is estimated from the radar variables using the volcanic ash radar retrieval for dual-polarization X band systems (VARR-PX) algorithm whereas BT's have been acquired from the Special Sensor Microwave Imager/Sounder (SSMIS). Model simulations of volcanic plume evolution are generated to carry out comparisons with radar estimates of TCC. The Active Tracer High-Resolution Atmospheric Model (ATHAM) of eruption plume is used for this purpose. Results show that high- spatial-resolution DPX radar data identify an evident volcanic plume signature, even though the interpretation of the polarimetric variables and the related retrievals is not always easy, likely due to the possible formation of ash and ice particle aggregates, the radar signal depolarization induced by turbulence effects, and the partial filling of the radar beam. A forth degree polynomial relationship is in good agreement with BT - TCC measured samples with correlation of -0.71. The variability of TCC, described by the ATHAM simulations, seems to include the spatial and temporal variation of the radar retrievals.