The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images

► HF-radar reflectors were observed in the limited areas consisting of about 9% of the whole maria. ► Model calculations indicate that the reflectors are not compositional interfaces but porosity boundaries. ► The reflectors in Mare Serenitatis lie on the boundaries between basalt units with different chemical compositions. ► The reflectors in Mare Serenitatis seem to be regolith accumulated during the long hiatus of mare volcanisms.