Noise analysis for ULTRASAT×DESI (pink), GALEX NUV×SDSS and ×DESI (light blue, dashed and continuous), and GALEX FUV×SDSS and ×DESI (dark blue, dashed and continuous). Left: 𝒩_CBR from Eq. (25). Here, we consider different sizes for the effective pixels. For each detector, the dot indicates the noise for L_pix as in Table 1, while the cross indicates the value adopted in the analysis. Right: S/N obtained from Eqs. (19) and (25).