Number of transits required to reach a S/N of 5 for the corresponding spectral features in a cloud free atmosphere with thin (solid lines) and thick (dashed lines) hazes using low-resolution transmission spectroscopy with JWST NIRSpec PRISM (upper and middle panels) and the cross-correlation technique with high-resolution transmission spectroscopy using ELT HIRES or METIS (lower panels). The x-axis of the upper panel is different from the middle and lower panels. Each colored circle corresponds to one scenario from Table 3. Blue lines and circles show low CH₄ scenarios, green lines and circles show medium CH₄ scenarios, and orange lines and circles show high CH₄ scenarios.