The detection of objects and the determination of their distance and speed by measuring the transit time, phase or frequency of the re-radiated electromagnetic waves. In most cases also the horizontal angle of radiation is measured.
Reference: N.T.G. (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
centre of gravity
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM