Identifying Surface Materials on an Active Volcano by Deriving Dielectric Permittivity From Polarimetric SAR Data

Dielectric permittivity $varepsilon_r$ measured on the Earth’s surface is an effective property for characterizing surface materials in terms of rock type and water content, particularly in highly changeable environments such as active volcanoes. We propose a technique termed dielectric permittivity from polarimetric synthetic aperture radar (dPSAR) to quantify $varepsilon_r$ using a single scene of polarimetric SAR data, based on the small perturbation model of backscattering (SPMB) . For an optimal solution, the Nelder–Mead simplex method was combined with SPMB. The application of dPSAR to a scene of ALOS PALSAR data from the vicinity of Mt. Merapi, Indonesia, correctly identified the relative value ranges of $varepsilon_r$ for pyroclastic flow and tephra deposits accompanying large eruptions that occurred on November 5, 2010; their means were 2.55 and 3.07, respectively. Pore water within porous ashes is a plausible factor for increases in the $varepsilon_r$ of the tephra.