Smooth 2-D frequency estimation using covariance fitting
In this paper, we introduce a non-parametric 2-D spectral estimator for smooth spectra, allowing for irregularly sampled measurements. The estimate is formed by assuming that the spectrum is smooth and will vary slowly over the frequency grids, such that the spectral density inside any given rectangle in the spectral grid may be approximated well as a plane. Using this framework, the 2-D spectrum