Final answer:
In aviation, when RVR data is not available, the alternative minimum ground visibility is ¾ SM. This standard is specified in the Federal Aviation Regulations for cases where RVR is not reported.
Step-by-step explanation:
The question relates to aviation visibility requirements, specifically when Runway Visual Range (RVR) is not reported. In aviation, RVR is a measure of the range over which a pilot of an aircraft on the centerline of a runway can see the runway surface markings or the lights delineating the runway or identifying its center line. When RVR data is not available, there are alternative minimum ground visibility standards that can be used. According to the Federal Aviation Regulations (FARs), the minimum ground visibility that may be used instead of a prescribed visibility criteria when that RVR value is not reported is ¾ SM (statute miles).