Matched Field Beamforming applied to Sonar Data
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Matchad lobformning för sonar data (Swedish)
Two methods for evaluating and improving plane wave beamforming have beendeveloped. The methods estimate the shape of the wavefront and use theinformation in the beamforming. One of the methods uses estimates of the timedelays between the sensors to approximate the shape of the wavefront, and theother estimates the wavefront by matching the received wavefront to sphericalwavefronts of diﬀerent radii. The methods are compared to a third more commonmethod of beamforming, which assumes that the impinging wave is planar. Themethods’ passive ranging abilities are also evaluated, and compared to a referencemethod based on triangulation.Both methods were evaluated with both real and simulated data. The simulateddata was obtained using Raylab, which is a simulation program based on ray-tracing. The real data was obtained through a ﬁeld-test performed in the Balticsea using a towed array sonar and a stationary source emitted tones.The performance of the matched beamformers depends on the distance to the tar-get. At a distance of 600 m near broadside the power received by the beamformerincreases by 0.5-1 dB compared to the plane wave beamformer. At a distance of300 m near broadside the improvement is approximately 2 dB. In general, obtain-ing an accurate distance estimation proved to be diﬃcult, and highly dependenton the noise present in the environment. A moving target at a distance of 600 mat broadside can be estimated with a maximum error of 150 m, when recursiveupdating of the covariance matrix with a updating constant of 0.25 is used. Whenrecursive updating is not used the margin of error increases to 400 m.
Place, publisher, year, edition, pages
2008. , 67 p.
Conventional Beamforming, Nearﬁeld, Bearing Estimation, Distance Estimation, Sonar, MUSIC, Linear array, Spatial Covariance Matrix, Matched Field
Other Electrical Engineering, Electronic Engineering, Information Engineering
IdentifiersURN: urn:nbn:se:liu:diva-16338ISRN: LiTH-ISY-Ex--08/4233--SEOAI: oai:DiVA.org:liu-16338DiVA: diva2:133957
2008-12-15, Glashuset, B-huset Linköping University, 15:00 (English)