http://hdl.handle.net/2123/983 Wed, 22 May 2013 03:13:18 GMT 2013-05-22T03:13:18Z http://hdl.handle.net/2123/5414 Title: Underwater Acoustic Imaging: Exact Geometric-Acoustics Treatment of the Image due to a Specular Reflector Authors: Blair, David G Abstract: In underwater acoustic imaging, used to produce high-resolution images in turbid waters, a specular reflector in general produces a 'pseudoimage' of the receiving array, located on the reflecting surface; the pseudoimage is of considerable use since it reveals the shape of the surface. A system is considered in which a spherical transmitter together with a 2D receiving array give a 3D image in a single 'ping'. A treatment predicting the shape of the pseudoimage - in particular, its lateral extent - is given that is exact within geometrical acoustics. The surfaces to which the treatment is applied are the paraboloid (with two principal radii of curvature) - provided that the transmitter lies on the paraboloid's axis - the sphere, the cylinder and the plane. The treatment involves a ray-tracing algorithm based on the equation of the surface, and an algorithm to invert that procedure using the Levenberg-Marquardt method. Pseudoimages of lines in the array are graphed and discussed, along with, more interestingly, pseudoimages of squares. While the latter pseudoimages are parallelograms when the square is small, in general they are not parallelograms, since all four sides are curved. Further features found are that an 'object' in the array may produce multiple pseudoimages, no pseudoimage, 'local optima' and/or 'blockage points'. Such an exact determination of the resulting pseudoimage for selected surfaces gives useful insight into pseudoimages that occur in practice. Conditions of validity (arising because wave effects are neglected) are given. The report also contains a preliminary discussion of the extension that would be needed to include wave effects. In addition it is shown that, subject to more restrictive conditions, the results apply also to a general smooth surface. A 'paraxial' approximation (similar to the 'large-range approximation' of an earlier paper but somewhat more general) is described and found to be useful. Wed, 23 Sep 2009 02:46:54 GMT http://hdl.handle.net/2123/5414 2009-09-23T02:46:54Z http://hdl.handle.net/2123/1897 Title: Desalination plants: Potential impacts of brine discharge on marine life Authors: Danoun, Rashad Abstract: Water has always been the earth's most valuable natural resource for human beings and ecosystems. Fresh water is an essential natural resource that supports human beings, flora and fauna habitat. Reductions in water quality and quantity have serious negative impacts on ecosystems. Over the past several decades, a tremendous growth in human populations and industrial activities has resulted in a significant demand for fresh and clean water. To meet these challenges and meet the pressures of demand it is critical to find a new alternative of water resource as the natural water resources have almost vanished. In spite of the high cost of desalinated water, an important quanity is already produced to meet the necessity for fresh water worldwide. Desalination could hold the key for new fresh water resources. Building more dams with significant sizable catchments would be a great solution in regards to supplying Australia with fresh water; however, many regions in Australia are facing a reduction in the rainfall and level of runoff. All the dams around Australia face a vast reduction in the storage level due to the diminishment of the inflow rate and the growth in water usage. Some arguments will be raised against building desalination plants on the grounds of environmental impacts to the surrounding area, especially to marine life due to the high concentrated brine discharge that diffuses back into the ocean. The impacts of the brine discharge are due to the high level of salinity and total alkalinity and alteration to the temperature. These impacts could be considerable in terms of the influence on the marine organisms such as the development of species, survival of larva and breeding and reproductive traits. However this paper provides some evidence that the influence of discharge for sesalination plant can be neglected in term of any environmental impact to the aquatic flora and fauna species. Tue, 31 Jul 2007 05:20:35 GMT http://hdl.handle.net/2123/1897 2007-07-31T05:20:35Z http://hdl.handle.net/2123/1863 Title: Sediment Concentration Measurement Authors: Roberts, James Oliver Abstract: Sydney Harbour is an important port and receational region for the City of Sydney. A study of water clarity is reported here. Water turbidity is influenced by the urban and industrial wastes that drain from the watershed and the flushing of the estuary by clear oceanic water. In order to contrast the imaging of objects underwater by light or sound, it is necessary to understand the role played by the scatterers in the water that cause turbidity. Using five reference sites, the grain size, the number of grains per litre and the turbidity have been compared before and after rain. Three Sydney area estuaries hve been observed to have similar turbidity increases with increasing distance from the sea. Wed, 11 Jul 2007 04:35:24 GMT http://hdl.handle.net/2123/1863 2007-07-11T04:35:24Z