SimSea (Norway)

The SIMRAD EM family of multibeam echo sounders are characterized by extremely wide swath widths with up to 190/spl deg/ angular coverage, high accuracy due to interferometric bottom detection, integrated sonar imaging (sidescan), and ease of operation. Continuous improvements of these systems are being made as a result of user experience and new requirements. Examples of requirements which have recently been addressed are the implementation of equidistant horizontal sounding pattern acrosstrack, and the capability of surveying all the way to the water surface along shorelines. Simrad Subsea has in the nineties sold 7 EM 12 deep sea systems, 11 EM 1000 intermediate depth systems, and 4 EM 950 shallow water systems, in addition to the 14 EM 100 systems delivered in the eighties, thus making Simrad the major manufacturer of multibeam echo sounder systems today. As the multibeam echo sounder systems are maturing, the efforts of both users and Simrad are shifting towards getting more out of the data collected, i.e. to improve the postprocessing and to find novel postprocessing methods, especially in the use of the sonar image data. This shift is reflected in this paper with a major part dedicated to the new generation of the Simrad postprocessing systems for multibeam echo sounder data. This includes both real-time processing and postprocessing of the EM echo sounder data to deliver end results such as bathymetry and sonar image visualization, charts, 3D views, sonar image mosaics, and seabed classification. >

The SIMRAD EM12 is a new full ocean depth multibeam echo sounder, operating at 13 kHz. By use of interf erometric signal processing techniques it will acheive an ultra wide swath geometry of 150 degrees, corresponding to 7 . 5 times the depth of water. The system will in addition to the bathymetry produce a fully corrected sidescan sonar image of the seafloor.on to the depth soundings, the EM12 has the capability to generate a sidescan image of the seabed. Basic Concepts

The paper gives a description of signal processing for wide swath mapping systems based on data obtained by delayed sampling giving inphase and quadrature components of the complex envelopes of the incoming signals. It includes a description of expected echo duration, phase information between two half beams which constitute one beam, receiving beamforming, amplitude and phase detection in each beam, and time-of-arrival estimation. Theoretical and measured values are compared. Measurements are made at 95 kHz for depths down to 500m.