-The Acoustic Research Laboratory (ARL) at the Tropical Marine Science Institute under the National University of Singapore has developed a second generation Ambient Noise Imaging (ANI) system: the Remotely Operated Mobile Ambient Noise Imaging System (ROMANIS). ROMANIS has been primarily developed to study the potential of ANI applications where snapping shrimp are the major natural insonifiers of the environment, as in warm shallow waters like those surrounding Singapore. ROMANIS is a fully digital broadband data acquisition and recording system with over 500 sensors that fully populate a circular aperture of 1.4m. The first at sea deployment was conducted during February 2003 to check the functionality of the system in a real seawater environment (that differs considerably in terms of electronic and acoustic noise from previous tests in tank) and to study the high frequency ambient noise characteristics at the deployment location. It was also required to validate the beamforming algorithms developed for imaging. A GUI-based application helps the user to control the acquisition process and acquire the data synchronously. Approximately 750 Mbytes of data was recorded. A custom software package has been developed which enables reading, processing and the displaying of images from the recorded data. In this paper we present the deployment details and preliminary analysis of the data. The analysis confirms that the energy distribution from snapping shrimp clicks follow a lognormal distribution as previously reported. The validity of the beamforming software has been verified with a 40 kHz pinging source placed some 50 m away from ROMANIS and forming an image of it from the data recorded. A second deployment of the system has been made during MayJune 2003 with targets placed at ranges exceeding any attempted to date and to produce their acoustic images. The data from these recordings are under analysis and some part of it is presented in this paper.
Abstract-The number of underwater activities and experiments in tropical waters has been growing; people are increasingly becoming interested in the development of underwater applications that rely on acoustic communications. Ambient noise is a limiting factor in the performance of underwater acoustic detection and communication systems at shallow water. Knowledge of ambient noise characteristics at a location will be helpful for ambient noise imaging systems like ROMANIS, built at Acoustic Research Laboratory.The Singapore straits and surrounding waters contain some of the busiest shipping channels in the world. Monitoring of ambient noise is of crucial interest to acousticians and oceanographers due to the high level of shipping and snapping shrimp noise in the region. Since there was no such systematic ambient noise database existing to support oceanographers and acousticians, the Acoustic Research Laboratory (ARL) at the Tropical Marine Science Institute (TMSI) has embarked on developing a shallow water ambient noise database. This Graphical User Interface (GUI) -based database will benefit and enhance the research and development of marine acoustic systems. This paper describes the collection of ambient noise data and the structured compilation of this information into a useful database. The data collected covers a frequency range of 11 -8300 Hz. The data is indexed and stored in a database and presented to the user via a GUI. The GUI uses an approach similar to typical Geographical Information System (GIS) databases. The user is able to select different layers of information on a map. The user may search for ambient noise data based on various parameters such as location of data collections or classification of the environment. The GUI is also integrated with Matlab ® , popular mathematical analysis software, to display the time series, power spectral density and 1/3 rd octave spectrogram of the ambient noise data.The database GUI, some example data and a summary of the collected ambient noise data will be presented. The high levels of noise due to shipping and snapping shrimp are all readily apparent in the data; with typical intensity levels considerably exceeding classic reported values. Shipping noise is reported to dominate the frequency range below 1 kHz. Snapping shrimp noise is found in all warm and shallow waters. The ambient noise data collected from near a fish farm area shows that the snapping shrimp noise is dominant above 2kHz.
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