The gradient’s norm measure of eq. E.2 is multiscale. Singularity spectra computed from the gradient norm measure as defined in eq. E.2 over three consecutively downscaled versions of the Musca observation map (filtered with parameters p = 1.5, q = −1, λ = 0.1) using a reverse bi-orthogonal discrete wavelet transform of order 4.4. The three spectra coincide, which means that the gradient’s norm measure is multiscale.