Abstract
Marine radar set at present uses the system of the P.P.I. presentation, which rotates continuously the scanner transmitting pulses in a narrow horizontal beamwidth, and which detects the targets in all directions while the set is in operation. Some seconds, however, are required for each revolution of the scanner, and the ship being under way for the time, and distortion of radar display by relative motion is produced in a short range. Nevertheless it has not been obvious, so we would research how much distortion will be produced by it. And taking this in a broad sense, we can consider that the change of a target's display between each revolution of a scanner is also the distortion. Some photographs are shown here, indicating these distortions described previously. We conclude that about 15 r.p.m. is the minimum speed of a scanner's rotation for the high speed vessel. Because the higher the speed of a vessel and the lower the one of a scanner's rotation, the larger is the distorting tendency.
