Long-pulse incoherent scatter probing of the F-region ionosphere at Arecibo
Incoherent scatter radar (ISR) experiments probing the F-region ionosphere at Arecibo utilize three types of transmission envelopes having different range-mixing and error statistical models on their corresponding backscattered pulse returns. The binary-coded envelope with wide bandwidth (0.44 ms duration and 220 bauds) enables measurement of the electron density spectrum at each 300-m range gate of the ionosphere, but the resulting spectra suffer from poor signal-to-noise and signal-to-clutter ratios. In contrast, the uncoded envelopes (0.5 ms and 1 ms durations) range-mix the electron density spectra within the transmitted pulse durations, reducing the effective range resolution from 300 m to 75 km and 150 km, respectively. Both the excessive measurement uncertainties in coded pulse transmissions and the range-mixing in uncoded pulse transmissions hinder accurate retrieval of ionospheric state parameters such as electron and ion temperatures, densities, and bulk drift velocities. This dissertation focuses on developing inversion procedures to mitigate these limitations, with the first stage addressing the coded pulse transmissions. The radar ambiguity functions of the pulses are analyzed to properly separate the 300-m ion-line spectra of target range gates from the frequency-spread clutter originating from adjacent gates within the pulse duration. A procedure is developed to mitigate the temperature-composition ambiguity encountered when inverting the separated ion-line spectra for F-region ionospheric state parameters under low-SNR conditions, using insights derived from a multi-dimensional "landscaping study" of the parameter space relevant to the F-region ionosphere. The procedure is demonstrated on the coded long pulse ISR data collected at Arecibo Observatory during the September 23-26, 2016 campaign, and the reliable range of extracted parameters is extended to approximately 600 km altitude. In the second stage, we develop a joint data inversion procedure that combines the scattered F-region returns from coded and uncoded pulse transmissions. The three sets of measured lag profile matrices are jointly inverted in a maximum-likelihood framework to enable the estimation of high-resolution F-region plasma parameters that governs the scattered signal spectra. The procedure incorporates the covariance matrices of the lag profile estimators, as well as the range mixing kernels specific to each transmission mode. The inversion procedure is applied to data collected during the same campaign as the first stage, extending the range of reliably estimated parameters to approximately 1400 km.
Incoherent scatter radar, Remote sensing, Signal processing
University of Illinois - Urbana-Champaign
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