1. In radio, a measure of the received radio frequency power; generally expressed in decibels relative to some standard value, normally either one milliwatt or that power that would have resulted at the same distance under free space transmission. Could also be applied to the strength of an optical signal transmitted or received by a lidar or an acoustic signal transmitted or received by a sodar. The term field strength is commonly used as a synonym. 2. In radar, the strength of the received signal, usually expressed in logarithmic power units, in particular decibels relative to 1 mW, that is, dBm.