Factors affecting error bounds in the use of high frequency radar for the remote sensing of the ocean surface: an analusis incorportating pulsed and frequency modulated continuous wave source

Norga, Moses (2013) Factors affecting error bounds in the use of high frequency radar for the remote sensing of the ocean surface: an analusis incorportating pulsed and frequency modulated continuous wave source. Masters thesis, Memorial University of Newfoundland.

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Abstract

In recent years, there has been a variety of research which has addressed the factors affecting the measurement of error bounds when using high frequency (HF) radar for ocean parameter measurements. The study presented here is conducted in order to identify other important factors that should also be considered in establishing meaningful error bounds on any ocean parameter extracted from the received radar signal. Specifically, this research aims at investigating the fluctuations in the Bragg peaks of the HF radar received spectra based on recent cross section models. -- The first part of the research work reviews the electric field equations for the backscattered signals when pulsed and frequency modulated continuous wave (FMCW) waveforms are used as transmitting waveforms. The incident radar signal is assumed to be scattered from the ocean surface, which is represented as a zero-mean Gaussian random process. Various operating parameters are selected to simulate the time series electric field for different conditions, and the power spectral densities (PSD) are calculated by the periodogram method. Again, an investigation is carried out to examine the signal to noise relationship in the Doppler spectra when a pulsed radar system has a noise limited reception. The noise is assumed to be external with no attempt to address internal noise features. It is assumed that the noise is an additive white Gaussian process. To develop the noise contaminated signal, a suitable noise model is incorporated in the time domain of the electric field signal. The Doppler spectra are calculated and examined for various signal to noise ratios. -- The second part of the research work examines the fluctuations in the Bragg peaks of the received Doppler spectra from the ocean surface. An investigation is first carried out for an ideal noiseless radar system. Choosing various operating frequencies, pulse widths (pulse waveform) and frequency bandwidths (FMCW waveform) for the simulations, numerical examinations of the existence of spectral fluctuations and Bragg distributions are conducted. The centroid positions of the Bragg peaks are calculated and compared with theoretical values to reveal the relative difference. To check the significance of the fluctuations, the standard deviations of the centroid positions of the Bragg regions are analyzed and compared to the resolution imposed by the fast Fourier transform (FFT). The results show that the standard deviations vary for various operating parameters of the radar. -- Finally, using the noise model introduced in the first part of the analysis, the investigation of the Bragg fluctuations is extended to a noise limited pulsed radar waveform. The standard deviations of the centroid positions are observed for different signal-to-noise ratios, operating frequencies and pulse widths. The significance of the noise level in the Bragg fluctuations is considered at the end of the analysis.

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