Multiple Scattering Visibility Specify the data to use to calculate directional visibility for multiple scattering:
• StrandProbe: Use strand count probes. This is the default mode.
• Shadowmap: Use the shadow map.

Both modes use strand count probes for the omnidirectional visibility term for multiple scattering. This property is visible only when you enable the Physical Material Type, the Strands Geometry Type, and Physical Scattering Mode.