Imaging the globe and its planetary neighbours by spacecraft has been admirably successful. The surface of the Moon and even of the planet Mars are mapped completely and in striking detail as well as the continents and islands of the Earth. Their formations and landscapes have been disclosed with the resolution of aerial photographs.
However, two-thirds of the globe is ocean, about 4 km deep, lying in total darkness. Radar and all other electromagnetic radiation don’t penetrate the sea. Visible light is the exclusive, but only very short sighted, exception. Photography, the source of all our fascination of marine fauna and flora, doesn’t reach farther than a hundred metres even in clear tropical waters. Mostly it is much less.
The only existing option to fully penetrate the otherwise impermeable water mantle is to see by sound. Sound in the sea, propagating with the least absorption of all mechanical waves on earth provides the only searchlight to irradiate the dark. Echosounding by ships has been developed to high resolution 3D-imagery in the recent years, enabled by global satellite positioning and computer capability. Multibeam systems scanning the sea floor to generate relief strips reveal fascinating structures and details never seen before. These images are no artist views and graphics, but real evidence of the dramatic and literally fundamental processes. For the first time the face of the hidden side of the earth can be visualized where new sea floor is permanently generated at the spreading ridges and slowly disappears at opposite sides of the tectonic plates into deep trenches, the entrance into the hot mantle of the earth. These subduction zones, the place of the largest forces of deformation in the biosphere of the globe, the origin of most of volcanism, earthquakes, and tsunamis are disclosed in their original formations and texture.
Imaging the ocean by sound is a unique key to reveal and understand the history, presence and future options of the dynamics of our own planet. But unlike the exploration of its exposed relief by satellites, ocean imaging by sound is inevitably slow, proceeding with the speed of ships. As yet only a small percent of the sea floor is covered by advanced high resolution imagery: The Earth is a still widely unknown planet. All the more it is the right time to try an interim balance: what has been achieved as yet? What conclusions can be drawn?
The book Sound Images of the Ocean is the first attempt to publish a comprehensive overview of the wide variety of acoustic applications in the fields of marine research, offshore economy, surveillance and protection of the ocean. This sound image collection covers a large number of subjects and sites of the world’s oceans and coastal waters and is interdisciplinary and international. More than 120 sound image authors and marine experts from 22 countries have contributed to the book. The subjects range from the scenarios of plate tectonics volcanism and hot spots to huge methane-hydrate deposits, from indications of ocean warming imaged by acoustic tomography to submerged cities and historic ship wrecks; from large submarine canyons to huge landslides; from sea lane surveillance and biomass monitoring to the reconnaissance of buried sea mines, from fish stocks to sound tracks of whale echosounding and communication; from sub-polar ice imaging to steering of the Gulf stream by undersea topography, and from the Arctic Ocean to Antarctica. Part of the conclusion is a plea for autonomous underwater vehicles, the advantages of which are demonstrated by impressive sound images.
Though sound imaging cannot yet offer the global high resolution relief of the ocean, the book nevertheless presents images of the complete globe, though in less detail. These reliefs are the result of a fascinating merger of two entirely independent methods: All available echosounder data - the sparse sounding lines in remote areas of the world as well as the denser measurements near coasts and sea lanes have been merged with satellite radar data of the sea surface relief, which provides a coarse copy of the sea floor beneath. The weak bulges and dents are generated by gravity anomalies which attract the sea volume above a submarine mountain slightly more than above a valley. The merger of these two independent data sets, combined to form a complete globe - a pioneering work by leading experts - is the best possible large scale overview at present of the nearly infinite variety of sea floor formations. This overview has become indispensable as a guide for site selection of follow-on high resolution acoustic close-ups of the outer relief and the structure below, to reveal the details of processes for further on-site research. The CD included with the book allows zooming and turning of the relief globe, as well as of very large sound images and sound tracks.
The book demonstrates the capability of the various technologies of sound imaging as diagnostic tools - similar to ultrasonics in medicine - but the aesthetic appearance of many of these images evokes appreciation beyond mere information. The book is intentionally written for the non-expert who may be a scientist from a neighbouring faculty. The intention is to raise and maintain interest in those formations and processes of the ocean which are beyond the access of photography - by far the majority.
Wille, Peter: Sound Images of the Ocean in Research and Monitoring. With contributions of 120 sound image authors and marine experts of 22 countries. Springer 2005. XLII, 472 p. 452 illus., 391 in color with CD-ROM., Hardcover ISBN: 3-540-24122-1, 129 $; 99.95 € plus VAT
Read here a Review by Larry Mayer (Center for Coastal and Ocean Mapping/NOAA-UNH Joint Hydrographic Center, USA).
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