1. Sonar Engineering - An orientation is provided which will indicate the scope and range of scientific and engineering applications of acoustics. A broad, non-technical description of the many engineering applications of sonar and underwater acoustics will provide an introduction to the material in the remainder of the course.

2. "Back to Basics": The Physics of Sound Propagation - Computer animations of particle motion will be used to establish a comprehensive understanding of wave propagation. The central role played by density and elasticity in sound propagation will be emphasised. The presentation of this material will be largely non-mathematical, emphasis being placed on an understanding of the physical processes involved. We shall introduce the acoustic version of "Ohm's Law" and then examine acoustical reflection and refraction laws.

3. Ray-Trace Propagation Modelling - Using the results of the previous lecture, we shall investigate the basic concepts of ray modelling which is one of many methods of approximating practical solutions to the Wave Equation. Examples of propagation through numbers of different ocean channels will be discussed in detail, using ray-modelling as our tool.

4. Key Quantities, Units and Dimensions - The ground rules concerning the often confusing systems of units used in underwater acoustics will be carefully established, with emphasis being placed on international standards. Power and energy concepts are of central importance to acoustic propagation, transducer design and waveform analysis and processing. Ranges and scales of the "size of acoustic events" will be presented, in terms of energy and power. This module will conclude with a comparison of the energy and power levels associated with the detonation of seismic surevey airguns, on the one hand, and the biosonar "pings" of the sperm whale, on the other.

5. Vibrations and Modes - Our target in this section is NOT lots of clever maths concerning signal processing. Acoustic signal spectra are now easily computed from time waveforms by readily available FFT software. Consequently, we shall NOT cover the many and various algorithmic incarnations and recursion formulae for this very widely used algorithm. Instead, we shall employ a functional "block-diagram" treatment of "how to make a music synthesiser" followed by "how to make a music analyser". This will lead us to a simple formulation of the Fourier Series equations used for analysing periodic waveforms.

6. Time and Frequency Domains - In this section we shall investigate representations of sinusoid and cisoid basic building-blocks for waveform synthesis. This will lead us to a relatively non-mathematical appreciation of the Sampling Theorem and also the reason why the Discrete Fourier Transform exists and what it does. The development of the FFT from the DFT will be outlined but will not be studied in detail. More detailed mathematical material, which will underpin this lecture and which is best digested "off-line", will be found in the accompanying text.

7. Energy and Power Spectra - The proper scaling, windowing and dimensioning of Power and Energy spectra is usually only poorly understood and rarely, if ever, mentioned in the mathematical texts on the topic. This is particularly the case in underwater acoustics, because of the plethora of systems of units employed. Our target will be an understanding of how to obtain dimensionally correct and well-conditioned spectrograms for Finite Power and for Finite Energy waveforms.

8. Signal Conditioning - An overview - at the “functional block level” of a comprehensive range of sonar signal processing hardware will be presented. Electronic modules which provide signal amplification, filtering, A/D conversion, signal processing and data storage will be reviewed.

9. Ambient Noise - All sonars have to be able to compete with ocean noise. Quantitative assessment of noise level provides a crucial input to the sonar equations. Audio samples and spectrograms of noise caused by earthquakes, surface waves, cracking ice, lightning strike, marine organisms, shipping and civil-engineering activities will be studied.

10. Biological and Environmental Origins of Reverberation - If the power of a sonar is increased to such a level that noise is no longer a problem then, inevitably, reverberation becomes the dominant corrupting influence. The origins of reverberation and its effect on the sonar will be discussed and compared with the effect of noise.

11. The "Sonar Equations" - Acoustic signals in the ocean lose energy because of spreading, friction and reflection from poor targets. The Sonar Equations provide a simple but practical set of design formulae for determining the impact of such losses. The delegate will learn how to use the Sonar Equations to develop performance estimates for numbers of sonars in common use. We shall discover how system performance may be estimated in the presence of noise and reverberation. We shall obtain evaluations of signal-to-noise ratio and signal-to-reverberation ratio for typical sonars. The point is made that, almost always, one or other phenomenon will dominate operation of a sonar. The impact of these quantities on the choice between active and passive sonar for a given requirement will be discussed.

12. ElectroAcoustic Transducers - An introduction to the structure and functioning of transmitter transducers will be provided which will include a practical account of piezoelectricity and the frequency range, general construction, tuning and frequency response of numbers of the commoner kind of underwater projector transducers.

13. Transducer Matching and Measurements -

14. Hydrophones - The fabrication and characteristics of hydrophones and their practical use in signal detection and transducer calibration will be presented.

15. Seismic Sources - Explosive charges, sparkers, boomers, sleeve guns and water guns will be briefly described. The modern airgun - now almost exclusively used in seismic survey - will be considered in detail, with attention being given to its wideband signature and frequency content. Arrays of airguns, their polar response, source level and directivity will also be studied

16. Transducer Arrays - Array construction will be described and the behaviour of the array will be discussed. Examples of commercial and military fixed and towed arrays, their purpose and characteristics will be explained. We shall also examine the practical specification of array aperture shading and element interspacing so that sidelobe and grating level targets are achievable and will discuss procedures for optimising both the physical array and its in-water response.