Although there is a geometrical relationship between slant visual range and RVR (or met vis), SVR is specific to the met conditions at that time; these vary considerably due to the nature of the fog structure (thickness/density), cloud type, snow, rain, etc. Thus SVR is not used for reporting – for practical purposes in normal operation it cannot be determined.
The first fig shows that SVR is independent of GS, depending on altitude, ‘fog thickness’, and RVR / met vis.
The second fig indicates the range of variation of SVR against RVR for extremes of ‘fog thickness’.
