Abstract: This paper studies the reconstruction of the absorptionproperties of a dense scattering medium fromtime-resolved data. A Progressive Expansion (PE)Algorithm, similar to a layer-stripping approach, hasbeen developed. The method progressively evaluatesincreasing depths within the medium by successivelyconsidering signals entering the detector at increasingtime following an incident pulse. In order to reducethe propagation of reconstruction errors occurring atshallower depths, an overlapping scheme is introducedwhich uses readings from several consecutive timeintervals in the reconstruction. In each overlappingtime interval, the region under consideration is solvedusing a perturbation approach recently described by ourgroup. The proposed algorithm is applied to severalinhomogeneous media containing simple structures. Twosets of data have been tested: one calculated accordingto the perturbation model; and the other by Monte Carlosimulations. The results show that the PE method, whencombined with proper overlapping, can make effectiveuse of the time-resolved data. Compared to our previousresults with steady-state data, the present methods canprobe deeper below the surface and produce a moreaccurate estimate.!22
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