Ambient noise imaging: Experiments with romanis, an ARL built underwater ANI camera

Abstract

The idea of using ambient noise for imaging underwater objects has been studied by many researchers, though not widely. The first Ambient Noise Imaging (ANI) camera namely ADONIS (Acoustic Daylight Ocean Noise Imaging System) was built in the Scripps Institute of Oceanography, USA and was tested out in the sea during 1994-96. The results obtained from field deployments demonstrated that ANI was indeed feasible by forming images of static underwater objects at a range of about 40m. Since then, DSTO Australia and ARL Singapore have been the only other two institutions that are known to have built their own ANI cameras and tested in the field. ARL deployed its ANI camera, Remotely Operated Mobile Ambient Noise Imaging System (ROMANIS), in 2003 and successfully produced images of static underwater reflecting targets placed at about 70m range from the camera; this is about twice the range reported from the ADONIS system. In 2009, ROMANIS and associated receiver systems were rebuilt for reliable field operations and fast processing so that near real-time images could be created. In May 2010, a month long experiment was conducted in Singapore waters using the new version of ROMANIS. Near real-time images of both static and mobile targets were obtained at ranges close to 100m from the camera during this deployment. In this paper we present the ROMANIS system architecture, beamforming techniques and processing approaches along with the results obtained from field trials conducted in 2010.