In radar meteorology, the motion of the radar antenna during data collection. Scanning usually follows a systematic pattern involving one of the following: 1) In horizontal scanning, used to generate PPI displays, the antenna is continuously rotated in azimuth around the horizon or is rotated back and forth in a sector (sector scanning); at the completion of each 360° or sector scan, the elevation angle of the scan typically is increased; 2) Vertical scanning, used to generate RHI displays, is accomplished by holding the azimuth constant while continuously varying the elevation angle of the antenna; at the completion of each vertical scan, the azimuth typically is incremented and the vertical scan proceeds in the opposite direction. See also volume scan.