Recovery of Spectral Moments from Overlaid Echoes in a Doppler Weather Radar

This paper presents a technique that enables the estimation of spectral moments of overlaid first and second trip weather echo signals in a pulsed Doppler radar. The transmitted pulses are phase coded with a sequence that allows manipulation of the signal spectrum in such a way that either the first or the second trip signal autocorrelation can be made zero, thus removing the bias error in mean velocity estimates due to overlaid echo. With a sufficiently large number of samples, desired mean velocities can be recovered using autocovariance processing provided that the interfering overlying echo power is not more than 10 dB higher than the desired echo power. Also presented is a spectral processing technique that, in conjunction with autocovariance processing, can recover all three spectral moments of both the first and second trip echoes, when their spectrum widths are narrow compared to the Nyquist interval and their power ratio is in the range ±15 dB. An algorithm is developed that can be easily implemented in existing Doppler radars, with the addition only of a lowpower switchable phase shifter and associated drive circuit.