Example of synthetic dataset analysed in Simulation 1 (containing wavelength-independent systematics) showing some simulated light curves (left) and recovered transmission spectrum (right). Left: the three shortest wavelength light curves in the dataset being fit by the transit model combined with a 2D GP noise model (the other 13 light curves were simultaneously fit but not plotted). Right: resulting transmission spectrum from the joint fit of all 16 light curves, with the three leftmost points corresponding to the light curves in the left plot. The recovered transmission spectrum was consistent with the injected spectrum (${\chi }_r^2=1.04$). An atmospheric retrieval was performed on the recovered transmission spectrum (with the best-fit model plotted) and was consistent with the flat slope and strong K feature of the injected spectrum.