Type of scan tells azimuth (a=) and elevation (e=) angles of VIL scanning patterns :
RHI = Range Height Indicator scan, i.e. elevational scan.
PPI = Plane Position Indicator scan, i.e. azimuthal scan.
VOL = Volume scan, several subsequent RHI's or PPI's forming a volume.
Comments tells visual observations or additional information about data cases. All times are in UT.