Echo Time Delay and Doppler Frequency

The time between transmission of a radar signal and reception of the echo is called the echo s roundtrip time delay, r, and is of order 2R/c, where c is the speed of light, 299,792,458 m sec . Since planetary targets are not points, even an infinitesimally short transmitted pulse would be dispersed in time delay, and the total extent Attarget of the distribution a(r) of echo power (in units of radar cross section) would be D jc for a sphere of diameter D and in general depends on the target s size and shape. 

FIGURE 5 Time-delay and Doppler-frequency resolution of the radar echo from a rotating spherical target. 

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