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Signal and noise level estimation for narrow spectral width returns observed by the Indian MST radar
Author(s) -
Hooper D. A.
Publication year - 1999
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/1999rs900041
Subject(s) - doppler effect , radar , remote sensing , spectral leakage , signal (programming language) , doppler radar , noise (video) , acoustics , physics , optics , geology , mathematics , computer science , telecommunications , algorithm , fast fourier transform , astronomy , artificial intelligence , image (mathematics) , programming language
Use is made of five sets of multibeam observations of the lower atmosphere made by the Indian mesosphere‐stratosphere‐troposphere (MST) radar. Two aspects of signal processing which can lead to serious underestimates of the signal‐to‐noise ratio are considered. First, a comparison is made of the effects of different data weighting windows applied to the inphase and quadrature components of the radar return samples prior to Fourier transformation. The relatively high degree of spectral leakage associated with the rectangular 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 found to be the most appropriate for these particular data. Second, a technique for removing systematic dc biases from the data in the time domain is compared with the more well‐known practice of correction in the frequency domain. The latter technique, which is often used to remove the effects of ground clutter, is shown to be particularly inappropriate for the characteristically narrow spectral width signals observed by the Indian MST radar. For cases of near‐zero Doppler shift it can remove up to 30 dB of signal information. 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.