An explicit second-order formula for radar echo time

In the radar ranging, the echo delay depends on the movements of the target and the transceiver during wave propagation. Thus, the exact formula for d etermining the radar echo time is implicit. In this investigation, the forw ard and the backward propagation times are expressed in terms of the separa tion distance of the target and the transceiver at the instant of wave emis sion. Thereby, an explicit second-order formula for the radar echo time is derived, which is helpful in high-precision radar, such as the interplaneta ry radar.