Fig. 1.

Temperature in k-space: $\widehat{T}\left(k,t\right)$ shows an exponential decay in time with $\text{exp}(-k^2\mathit{\alpha }t)$. At $k_{\mathrm{cut}}$ it goes below the noise level. For the reconstruction only the wavenumbers less than $k_{\mathrm{cut}}$ are taken