Pearson correlation coefficient ${\mathcal{C}}_{LL\prime }/\sqrt{{\mathcal{C}}_{\mathit{LL}}{\mathcal{C}}_{L\prime L\prime }}$ where 𝒞_LL′ is the covariance matrix. White noise and foreground removal systematic effects included. As in the pure 21 cm case, the correlation decreases with frequency channel. For the latest frequency channels, the correlation decreases for multipoles above ℓ ≈ 100 due to the deacrease of the signal-to-noise ratio. Additionaly for the earliest channels, the correlations remain high as an effect of foreground removal.