Noise--Measurement

This thesis describes a series of measurements that took place over the duration of one year on the South Florida Testing Facility (SFTF) range, Dania, in order to survey the shallow water ambient acoustic environment. Three groups of data sets were taken in December 1998, May 1999 and July 1999. The data was collected using the Ambient Noise Sonar (ANS) that was developed in the Ocean Engineering department at Florida Atlantic University. The ambient acoustic environment was found to be highly variable with two main components. Boat noise was found to primarily be associated with the inlet and a source of snapping shrimp situated on the shallow water 30ft reef became apparent through 24hr observation. The effects of adverse weather were not studied due to the absence of this source during the measurement periods.

A theoretical model has been developed to compute the vertical array directional response for surface generated ambient noise in a shallow water environment. The cross spectrum function is based on a normal mode solution to the wave equation in which the effective depth approximation is used to yield closed form solutions for two distinct mode types. The effective depth modes encompass the shallowest grazing angles where the bottom reacts as a pressure release surface to the incident plane waves. The rigid bottom solution takes over as the grazing angle increases and attenuation becomes significant. The computed vertical array beam output was compared to other models including a fast field wavenumber integration method and a multipath eigenray method with mixed results. The results indicated good agreement for both comparisons with the realization that the effective depth model is sensitive to the approximation discontinuity at the mode transition point.

It has been conjectured that the addition of negative
feedback in an oscillator can reduce the noise generated at
frequencies close to the oscillation frequency f0. In this
thesis the noise of a bipolar transistor used in a Hartley
oscillator configuration is measured for different values of
unbypassed emitter resistance. It is found that the noise is
substantially reduced as the negative feedback introduced by
the emitter resistance is increased. A detailed noise
analysis is included, the results of which predict t he
observed reduction in the oscillator noise. The oscillation
frequency of the test oscillator is approximately 50 Mhz, but
the results are general and can be applied at any frequency.
Included are two listings of computer programs that were u sed
to perform the noise analysis.