2-D Acoustic Full Waveform Ambient Noise Inversion

We present a 2-D ambient noise full waveform inversion technique based on noisecross-correlation sensitivity kernels. These kernels are constructed through the adjoint statemethod, using a time-domain finite-difference solver to simulate both forward andadjoint acoustic wavefields. Both the ambient noise source distribution and velocity structureare treated as unknown. The inversion for source, and then structure parameters iscarried out sequentially. This sequential inversion is based on waveform energy misfit inthe case of noise source and cross-correlation travel time misfit in the case of velocitystructure. The present study focuses on applying this ambient noise full waveform inversionmethodology at local scales.We use this approach to image the velocity structure beneath the Lonar crater in India.This basaltic impact crater has close geological analogs on the Moon, and its internal structureprovides an important benchmark for assessing geometric models of crater formation.We compare the results from our inversion with those obtained using conventional ambientnoise interferometry, which relies on Green’s function retrieval.