Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The process that changed the radar backscatter between the pre- and the post-event images is ascribable to the changes of the land cover structure, roughness at the wavelength scale of the C band, and the change of the land dielectric constant (moisture content) in the passage from dense canopy to bare soil [13,19] caused by event landslides.
Category: