Signal and noise level estimation for narrow spectral width returns observed by the Indian MST radar

Use is made of five sets of multibeam observations of the lower atmosphere made by the Indian mesosphere-stratosphere-troposphere (MST) radar. Two asp ects of signal processing which can lead to serious underestimates of the s ignal-to-noise ratio are considered. First, a comparison is made of the eff ects of different data weighting windows applied to the inphase and quadrat ure components of the radar return samples prior to Fourier transformation. The relatively high degree of spectral leakage associated with the rectang ular and Hamming windows can give rise to overestimates of the noise levels by up to 28 dB for the strongest signals. Use of the Hanning window is fou nd to be the most appropriate for these particular data. Second, a techniqu e for removing systematic de biases from the data in the time domain is com pared with the more well-known practice of correction in the frequency doma in. The latter technique, which is often used to remove the effects of grou nd clutter, is shown to be particularly inappropriate for the characteristi cally narrow spectral width signals observed by the Indian MST radar. For c ases of near-zero Doppler shift it can remove up to 30 dB of signal informa tion. The consequences of noise and signal level discrepancies for studies of refractivity structures are discussed. It is shown that neither problem has a significant effect on Doppler shift or spectral width estimates.