Feasibility of three-dimensional density tomography using dozens of muon radiographies and filtered back projection for volcanos

Abstract

This study is the first trial to apply the method of filtered back projection (FBP) to reconstruct three-dimensional (3-D) bulk density images via cosmic-ray muons. We also simulated three-dimensional reconstruction image with dozens of muon radiographies for a volcano using the FBP method and evaluated its practicality. The FBP method is widely used in X-ray and CT image reconstruction but has not been used in the field of muon radiography. One of the merits of using the FBP method instead of the ordinary inversion method is that it does not require an initial model, while ordinary inversion analysis needs an initial model. We also added new approximation factors by using data on mountain topography in existing formulas to successfully reduce systematic reconstruction errors. From a volcanic perspective, lidar is commonly used to measure and analyze mountain topography. We tested the performance and applicability to a model of Omuroyama, a monogenetic scoria cone located in Shizuoka, Japan. As a result, it was revealed that the density difference between the original and reconstructed images depended on the number of observation points and the accidental error caused by muon statistics depended on the multiplication of total effective area and exposure period. Combining all of the above, we established how to evaluate an observation plan for volcanos using dozens of muon radiographies.