Resolution and denoising in near-field imaging

We consider the inverse problem of reconstructing surface displacements from noisy acoustic measurements collected at a distance from the surface that is comparable to the wavelength. As the detectors move closer to the surface and information from evanescent waves is recorded, the resolution of the image improves up to a level that is limited by the signal-to-noise ratio (SNR). We review this basic trade-off in near-field imaging with narrowband signals and then extend it to broadband signals. We find that the resolution in broadband near-field imaging is enhanced because the SNR effectively increases with increasing bandwidth. We present the results of numerical simulations to illustrate this enhancement of the resolution.