A 2D synchronous spectrum expresses the similarity between spectral of the data in the original dataset. In generalized 2D correlation spectroscopy this is mathematically expressed as covariance (or correlation).
where:
*Φ is the 2D synchronous spectrum
*ν and ν are two spectral channels
*y is the vector composed of the signal intensities in E in column ν
*n the number of signals in the original dataset