These routines estimate the wavenumber-frequency spectrum S(K,f) using the method described in J. M. Beall et al, Estimation of wavenumber and frequency spectra using fixed probe pairs
Journal of Applied Physics 53, 3933 (1982).
pip install git+https://github.com/smartass101/xrbeall
See this usage example Jupyter notebook for an example with 2 signals containing harmonics with a cubic dispersion relation.