Correlation function measurements for incoherent scatter radar

Incoherent (Thomson) scattering is scattering of VHF or UHF radio waves produced by the thermal fluctuation of plasmas and is used as a diagnostic tool for studying the different regions of the ionosphere. There are two systems to receive the scattered signal: one, the filter-bank method (FBM), measures a power spectrum directly using a bank of filters; the other, the correlation-function method (CFM), calculates the autocorrelation function (ACF) from a time-varying signal, which is the Fourier transformation of the power spectrum. Systematic distortions of the spectrum due to the finite transmitted pulse duration are estimated using the radar ambiguity function. It is shown that in the CFM, the resolution in altitude is uniquely determined by the pulse duration and its frequency by the pulse spacing. The random statistical error in the 15 autocorrelation functions was also formulated.