This work deals with the spectrum parameters estimation of a weather radar signal, namely velocity, variance and spectrum width. A new tool - based on the Ramanujan sums, cq(n), which come from the arithmetic functions of the number theory - has been introduced in signal processing. As compared to pulse pair and Fourier algorithms, new results have been obtained by the use of the Ramanujan-Fourier Transform (RFT) for the Doppler spectrum estimation of a real weather data provided by terminal pulse Doppler radar (WSR-88D).