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Acoustic waveguides: Applications to ocean science
598 ACOUSTIC
Chichester,
BOOK WAVEGUIDES:
Sussex:
John
APPLICATIONS
REVIEWS TO
SCIENCE by C. Allan Boyles 1984. Price X44.60. ISBN 0 471 887714.
OCEAN
Wiley & Sons Limited.
As will become apparent, C. Allan Boyles has written a book with an individual style and choice of material. His object is to expose the theory of acoustic propagation in oceanic waveguides. The work is intended to be used at the first-year graduate level as an introductory text, being based on a course taught at Johns Hopkins. First we will scan through the seven chapters. Chapter 1 on the fundamental equations of fluid motion includes a very detailed derivation of the acoustic wave equation. This careful presentation is stated to be one of the main reasons for the book, since everything else may be considered to flow from the wave equation. Thus, if the reader can understand the assumptions and methods here, all else is downhill. Chapter 2 is a mathematical review concentrating on differential equations. There is useful material here but it might be difficult for the novice working through the book to accept the relevance of all the difficult mathematics: e.g., in the long section on Bessel functions he does not admit at this stage to any connection with cylindrically spreading normal modes. At the end of these two chapters we are one-third of the way through the book, having encountered much mathematics but no waveguides. But in chapter 3 we really do start, seeking an exact solution to the wave equation in a homogeneous layered model. The first approach is by way of the complex A-plane representation of the Green’s function, and it may be wondered why the author is seeking the solution to a relatively trivial problem by the most difficult method he could find. In fact his solution is an eigenfunction expansion reached without mentioning eigenfunctions, though these are brought in with his second approach. The general viewpoint is illuminating in showing the relationships between approaches, and it is good to have this account available in an accessible form: Chapter 4 moves on to the inhomogeneous layered model, and together with chapter 3 could be considered the heart of the book. Interesting treatments of the ray and the WKB approximations appear in chapter 5. I have the impression that Boyles disapproves, and that he disapproves most strongly, of the approximations involved in the real world, which is notoriously unreliable as a producer of tidy solutions to the wave equation. It is in this chapter that he comes closest to sullying his book with experimental data-citing but not illustrating the agreement with a ray program corrected for smooth caustics. Chapter 6 shows applications of the previous theory, and does this by looking at length at just three realistic ocean environments: a Pacific profile with a single deep channel, an Atlantic profile with a double channel, and an Atlantic profile with a strong surface duct. As an example of the book’s style, note that there are for this last profile 53 normal modes trapped in the water column at 60 Hz, and for all 53 the eigenvalues and phase velocities are tabulated to 16 significant figures. Then we have a corresponding list at 30 Hz, and another at 10 Hz. Chapter 7 presents an account of Boyle’s own original coupled-mode work on a range-dependent waveguide. We learn that the work is so new that no numerical examples are available, which is a pity. Perhaps my major comment on the book is its selectivity in subject matter. The title is not very informative but we can deduce from the preface that we should expect nothing on ambient noise, nor reverberation, nor anything experimental. In practice we find nothing on the methods of the parabolic equation, fast field program, finite element method nor transport equation: nothing on the subjects of group velocity, coherence, fluctuations, shallow water, ice cover, etc. There is very little on the vital subject of bottom structure and properties. I do not ask for all these aspects to be treated, but for a graduate text would like to have seen some comments on what is omitted as well as what is covered.
BOOK REVIEWS
599
Is it an accurate book? Yes, I have not been struck by specific mistakes. Is it a difficult book to read? Yes, largely due to the subject matter. Sometimes Boyles leaves long pages of mathematics almost to speak for themselves and this can be very successful-but not always. Is it a useful book, suitable as a textbook? The answer is complicated-it could certainly be used as a textbook with a choice regarding the extras such as chapter 2, but I believe it should not be used alone. It is a nice book to have for a worker in theoretical acoustics.
D. E. WESTON
Chichester,
BOOK WAVEGUIDES:
Sussex:
John
APPLICATIONS
REVIEWS TO
SCIENCE by C. Allan Boyles 1984. Price X44.60. ISBN 0 471 887714.
OCEAN
Wiley & Sons Limited.
As will become apparent, C. Allan Boyles has written a book with an individual style and choice of material. His object is to expose the theory of acoustic propagation in oceanic waveguides. The work is intended to be used at the first-year graduate level as an introductory text, being based on a course taught at Johns Hopkins. First we will scan through the seven chapters. Chapter 1 on the fundamental equations of fluid motion includes a very detailed derivation of the acoustic wave equation. This careful presentation is stated to be one of the main reasons for the book, since everything else may be considered to flow from the wave equation. Thus, if the reader can understand the assumptions and methods here, all else is downhill. Chapter 2 is a mathematical review concentrating on differential equations. There is useful material here but it might be difficult for the novice working through the book to accept the relevance of all the difficult mathematics: e.g., in the long section on Bessel functions he does not admit at this stage to any connection with cylindrically spreading normal modes. At the end of these two chapters we are one-third of the way through the book, having encountered much mathematics but no waveguides. But in chapter 3 we really do start, seeking an exact solution to the wave equation in a homogeneous layered model. The first approach is by way of the complex A-plane representation of the Green’s function, and it may be wondered why the author is seeking the solution to a relatively trivial problem by the most difficult method he could find. In fact his solution is an eigenfunction expansion reached without mentioning eigenfunctions, though these are brought in with his second approach. The general viewpoint is illuminating in showing the relationships between approaches, and it is good to have this account available in an accessible form: Chapter 4 moves on to the inhomogeneous layered model, and together with chapter 3 could be considered the heart of the book. Interesting treatments of the ray and the WKB approximations appear in chapter 5. I have the impression that Boyles disapproves, and that he disapproves most strongly, of the approximations involved in the real world, which is notoriously unreliable as a producer of tidy solutions to the wave equation. It is in this chapter that he comes closest to sullying his book with experimental data-citing but not illustrating the agreement with a ray program corrected for smooth caustics. Chapter 6 shows applications of the previous theory, and does this by looking at length at just three realistic ocean environments: a Pacific profile with a single deep channel, an Atlantic profile with a double channel, and an Atlantic profile with a strong surface duct. As an example of the book’s style, note that there are for this last profile 53 normal modes trapped in the water column at 60 Hz, and for all 53 the eigenvalues and phase velocities are tabulated to 16 significant figures. Then we have a corresponding list at 30 Hz, and another at 10 Hz. Chapter 7 presents an account of Boyle’s own original coupled-mode work on a range-dependent waveguide. We learn that the work is so new that no numerical examples are available, which is a pity. Perhaps my major comment on the book is its selectivity in subject matter. The title is not very informative but we can deduce from the preface that we should expect nothing on ambient noise, nor reverberation, nor anything experimental. In practice we find nothing on the methods of the parabolic equation, fast field program, finite element method nor transport equation: nothing on the subjects of group velocity, coherence, fluctuations, shallow water, ice cover, etc. There is very little on the vital subject of bottom structure and properties. I do not ask for all these aspects to be treated, but for a graduate text would like to have seen some comments on what is omitted as well as what is covered.
BOOK REVIEWS
599
Is it an accurate book? Yes, I have not been struck by specific mistakes. Is it a difficult book to read? Yes, largely due to the subject matter. Sometimes Boyles leaves long pages of mathematics almost to speak for themselves and this can be very successful-but not always. Is it a useful book, suitable as a textbook? The answer is complicated-it could certainly be used as a textbook with a choice regarding the extras such as chapter 2, but I believe it should not be used alone. It is a nice book to have for a worker in theoretical acoustics.
D. E. WESTON