Laboratory photometry of planetary regolith analogs -: II.: Surface roughness and extremes of packing density

Laboratory phase curves of planetary regolith analog materials are presented. A study is made of the effect of compaction of the material on its backscattering properties. Further study is also made of the contribution of material surface roughness on its light scattering. First photometric light backscattering measurements in a microgravity environment are introduced as well as some improvements of the laboratory experiment techniques. The measurements show a strong increase in both reflectance and opposition effect amplitude under compaction. Also a broadening of the opposition effect width is observed. These results are in contrast with some of the previous studies on the subject. The surface roughness of a sample is found to be an important factor in measurements of samples with the same packing density. This should be taken into account in further studies.