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Part I has been published as: Zetterberg, Viktoria and Pettersson, Mats I. and Claesson, Ingvar, Comparison between whitened generalized cross correlation and adaptive filter for time delay estimation with scattered arrays for passive positioning of moving targets in Baltic Sea shallow waters, In proceedings of Oceans 2005 MTS/IEEE Conference ”One Ocean”, Washington DC, USA, September 2005.
Comparison between whitened generalized cross correlation and adaptive filter for time delay estimation with scattered arrays for passive positioning of moving targets in Baltic Sea shallow waters 29 Comparison between whitened generalized cross correlation and adaptive filter for time delay estimation with scattered arrays for passive positioning of moving targets in Baltic Sea shallow waters V. Zetterberg Amlab Elektronik AB Nettovaegen 11, Jaerfaella, Sweden Phone: +46 70 4411220 Email:viktoria.zetterberg@amlab.se M. I. Pettersson Department of Signal Processing, School of Engineering, Blekinge Institute of Technology Soft Center, Ronneby, Sweden Phone: +46 457 385728 Email:mtp@bth.se I. Claesson Department of Signal Processing, School of Engineering, Blekinge Institute of Technology Soft Center, Ronneby, Sweden Phone: +46 457 385717 Email:ingvar.claesson@bth.se Abstract - Results from an acoustic measurement campaign in shallow waters (at 22 meters depth) are given. Eight hydrophones, placed at the seabed, were used simultaneously to investigate how different distances between hydrophones affect the Time Delay Estimation (TDE). In order to position targets two TDE methods were applied. The Generalized Cross Correlation (GCC) function weighted by the Phase Transform (PHAT) and an adaptive Normalized Least Mean Square (NLMS) filter estimating the TDE between pairs of sensors. The two methods gave approximately the same result, except for the largest baseline where the GCC PHAT performed better. In the study we found that increasing separation distance decrease the bandwidth of coherence between the signals, however the study also indicated that scattered arrays with large baselines has better positioning capability than those with small baselines. I. INTRODUCTION The benefit of using larger arrays is coverage of larger areas using the same amount of sensors and giving higher positioning accuracy assuming equal coherence. In this paper we try to analyze how much the result is affected by larger separation distances of hydrophones by using real measurement data. The commonly used way for localization of a sound source is by using linear arrays with small baselines. Little work seems to be conducted about widely and randomly distributed sensors. Xerri, Cavassilas and Burloz [1] have though positioned moving broad band sources with sensors distributed about 400 m in average from each other at dept 250 m. Time Delay Estimation (TDE) between at least two different pairs of spatially separated sensors is a robust and computationally practical way [2] that leads to the positioning of a sound source. Since the estimation is the first step, the quality of the estimation affects the rest of the result [3]. By using real measurement data, a result of TDE by two different methods for different baselines is presented. The purpose is to investigate how the TDE is affected by the size of the baseline in shallow waters. Adaptive filters for TDE eliminating multipath have been studied since the beginning of the 1980’s, results from simulated data can be found in e.g. [4,5]. Results from measurements of underwater data are though hard to find. We here present results from The Normalized Least Mean Square (NLMS) adaptive filter [6] applied to underwater measurement data and compared to results from the Generalized Cross Correlation function (GCC) [7], weighted by the Phase Transform (PHAT) [8]. A similar study has earlier been done [9] where simulated data were used. II. MEASUREMENT The measurement site was at the Swedish coastline of the low salinity Baltic Sea at a depth of 22 meters. Eight hydrophones formed three equilateral triangles with three different bases, d equal to 0.5, 9 and 30 meters. The hydrophones were omni-directional and placed at 0.5 meters above the seabed. A sampling frequency of 48 kHz with a receiver dynamic range of 16 bits was used. H8 H7 ~30m ~30m H3 Fig. 1 During the experiment, eight hydrophones was placed at the seabed. Hydrophones 4-5-6 form an equilateral triangle with a baseline of 0.5 m. Hydrophones 1-2-3 form the equilateral triangle with the baseline of 9 m. Hydrophones 3-7-8 form a triangle with a baseline of 30 m. H4 H5 r=0,275m H6 r=5,07m H2 H1
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ABSTRACT Surveillance of sound acti
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