Spectral trend due to soil compaction computed based on the model by Hapke (2008). The darkest line in each plot corresponds to the measured spectrum. The brighter spectra are modeled based on the filling factor of the model by Hapke (2008) with increasing soil compaction. Panel a: mature mare spectrum (average of 1 km² area at 14.167° E, 21.700° N). Panel b: mature highland spectrum (average of 1 km² area at 182.400° E, 2.233° N). The filling factor ranges from 0 (bottom curve) to 0.6 (top curve) in steps of 0.1.