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Joint inversion of muon tomography and gravimetry - a resolving kernel approach
Both muon tomography and gravimetry are geophysical methods that provide
information on the density structure of the Earth's subsurface. Muon tomography
measures the natural flux of cosmic muons and its attenuation produced by the
screening effect of the rock mass to image. Gravimetry generally consists in
measurements of the vertical component of the local gravity field. Both methods
are linearly linked to density, but their spatial sensitivity is very
different. Muon tomography essentially works like medical X-ray scan and
integrates density information along elongated narrow conical volumes while
gravimetry measurements are linked to density by a 3-dimensional integral
encompassing the whole studied domain. We develop the mathematical expressions
of these integration formulas -- called acquisition kernels -- to express
resolving kernels that act as spatial filters relating the true unknown density
structure to the density distribution actually recoverable from the available
data. The resolving kernels provide a tool to quantitatively describe the
resolution of the density models and to evaluate the resolution improvement
expected by adding new data in the inversion. The resolving kernels derived in
the joined muon/gravimetry case indicate that gravity data are almost useless
to constrain the density structure in regions sampled by more than two muon
tomography acquisitions. Interestingly the resolution in deeper regions not
sampled by muon tomography is significantly improved by joining the two
techniques. Examples taken from field experiments performed on La Soufri\`ere
of Guadeloupe volcano are discussed.Comment: Submitted to Geoscientific Model Developmen
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