Hapke's photometric theory is fitted to Voyager whole disk observatios of Miranda, Ariel, Umbriel, Titania, and Oberon to obtain better determinations of the satellites' geometric albedos and phase integrals. Our analysis demonstrates that in terms of large-scale roughness, Umbriel, Titania, and Oberon are comparable to our Moon, but Ariel is significantly rougher. The most conspicuous difference among regolith parameters is the particle single scattering albedo (values range from 0.3 for Umbriel up to 0.7 for Ariel). On the other hand, the degree of backscattering of regolith particles is found to be very similar (values of the Henyey-Greenstein parameter g are all close to −0.3). Umbriel's opposition surge appears to be marginally detectable in Voyager observations. Our tentative results suggest that Umbriel's opposition surge is lunar-like and distinctly broader than Titania's. This would imply that Umbriel's regolith is less porous than Titania's and its solid particles are less strongly backscattering (g = −0.2).
