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The Effect of Transmitter Pulse Width on Bragg Positions in Pulsed Doppler Radar


J. Zhang, E. Gill, and J. Walsh
Memorial University of Newfoundland, St. John's, NL Canada A1B 3X5


Abstract Recent cross section models of the ocean surface, which describe the first order scatter process when the transmitted signal is a pulsed sinusoid, naturally include broadened Bragg peaks in terms of sampling functions. While this is well-known to be the case in practice, the classical cross sections have described this phenomenon in terms of delta functions. If the ocean surface is cast as a zero-mean Gaussian random process, it is seen that Fourier transformation of the electric field for discrete time intervals results in fluctuation of the centroid frequencies of the Bragg regions in the resulting Doppler spectrum. Here, it is shown that a fundamental reason for this variability lies in the the fact that the contribution to the power spectrum at each Doppler frequency point is randomly affected by that at neighboring points. The standard deviation of the centroid frequency is determined to be a function of pulse width and operating frequency. This, of course, will provide one of the components necessary in developing error bars for surface currents deduced from pulsed radar data. Similar work is ongoing to extend these ideas to frequency modulated systems.

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