Gabor Gereb

• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes & Kirkebø, Jan Egil (2023). Beampattern bounds for block errors in sonar arrays using interval arithmetic. OCEANS. ISSN 0197-7385. doi: 10.1109/OCEANSLimerick52467.2023.10244467.
• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2023). Worst-case analysis of array beampatterns using interval arithmetic. Journal of the Acoustical Society of America. ISSN 0001-4966. 153(6), p. 3312–3323. doi: 10.1121/10.0019715. Full text in Research Archive Show summary

  Over the past decade, interval arithmetic (IA) has been used to determine tolerance bounds of phased-array beampatterns. IA only requires that the errors of the array elements are bounded and can provide reliable beampattern bounds even when a statistical model is missing. However, previous research has not explored the use of IA to find the error realizations responsible for achieving specific bounds. In this study, the capabilities of IA are extended by introducing the concept of “backtracking,” which provides a direct way of addressing how specific bounds can be attained. Backtracking allows for the recovery of the specific error realization and corresponding beampattern, enabling the study and verification of which errors result in the worst-case array performance in terms of the peak sidelobe level (PSLL). Moreover, IA is made applicable to a wider range of arrays by adding support for arbitrary array geometries with directive elements and mutual coupling in addition to element amplitude, phase, and positioning errors. Last, a simple formula for approximate bounds of uniformly bounded errors is derived and numerically verified. This formula gives insights into how array size and apodization cannot reduce the worst-case PSLL beyond a certain limit.

• Gereb, Gabor & Arnestad, Håvard (2023). Interval computations in acoustics. In Viggen, Erlend Magnus (Eds.), Proceedings of the 46th Scandinavian Symposium on Physical Acoustics. Norsk Fysisk Selskap. ISSN 978-82-8123-023-1.
• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2022). Sonar array beampattern bounds and an interval arithmetic toolbox. Proceedings of Meetings on Acoustics (POMA). ISSN 1939-800X. 47. doi: 10.1121/2.0001613. Show summary

  The framework of interval arithmetic (IA) and its extension to complex numbers has in the last decade been applied as a tool for finding robust tolerance bounds of antenna arrays. The IA framework complements statistical methods, as inclusive upper and lower bounds of the beampattern are obtained directly, only assuming error bounds on specifically chosen array parameters. Recently, beampattern synthesis for sonar arrays subject to amplitude excitation errors has been extended from linear arrays with omnidirectional elements to non-linear arrays with directive elements. In this work, we demonstrate that the analysis can be developed further to include both amplitude and phase errors. Moreover, we account for error bounds in element position and orientation, thus representing a more comprehensive method for evaluating the worst-case performance due to uncertainty bounds in a multitude of design parameters. For this purpose, we have created an open-source MATLAB toolbox to calculate beampattern bounds for an array with bounded error tolerances. The toolbox features an object oriented library of interval classes and an interactive graphical user interface with easily configurable settings, where results for different interval representations are shown along with their corresponding bounds. The beampattern bounds of a sonar array is illustrated through an example.

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• Gereb, Gabor; Austeng, Andreas; Hansen, Roy Edgar & Birkenes Lønmo, Tor Inge (2024). Resolution of adaptive beamformers.
• Gereb, Gabor; Austeng, Andreas; Hansen, Roy Edgar & Birkenes Lønmo, Tor Inge (2023). Performance analysis of adaptive beamformers in surveying pipelines by multi-beam echo sounders​.
• Gereb, Gabor & Arnestad, Håvard (2023). Interval computations in acoustics.
• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2023). Bounding the beampattern of acoustic arrays using interval arithmetic.
• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2022). Bounding the beampattern of acoustic arrays using interval arithmetic.
• Gereb, Gabor; Hansen, Roy Edgar; Austeng, Andreas; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter & Rindal, Ole Marius Hoel (2022). Ultrasound Beamformer Benchmarking Pipeline.
• Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter; Austeng, Andreas & Rindal, Ole Marius Hoel (2022). Improving Sonar Surveying of Subsea Cables and Pipelines with Adaptive Beamforming. Show summary

  Background, Motivation and Objective Safe and efficient transportation of offshore energy requires well-maintained underwater infrastructure, no matter if the energy source is fossil, wind, sun, or wave. Subsea cables and pipelines can be efficiently surveyed using sonar systems mounted on surface or underwater vehicles. Adaptive array signal processing methods are increasingly explored to improve image quality and detection or estimation accuracy in specific survey scenarios. However, adaptive methods can be sensitive to the context they are used in. Therefore, choosing the right beamforming approach from the available candidates requires extensive testing in various scenarios, which is often not feasible out at sea. Statement of Contribution/Methods Realistic simulation of complex underwater scenarios has been previously demonstrated using the Field II Ultrasound Simulation Program in combination with the open access package UltraSound ToolBox (USTB). We use Field II to create digital twins of water column images from pipeline surveys, and then modify parameters such as the layout, depth, and SNR to extend the scope of testing. We add multiple realizations of random noise to the signal and then use USTB to beamform the data with different techniques. On the beamformed data we perform estimation of multiple parameters such as the position and size of the pipe and the seabed depth around it. Finally, using the known ground truth of the model, we compare the bias and variance of the estimations made using images reconstructed by different beamformers. Results/Discussion Following on the results of previous studies demonstrating the benefits of adaptive beamforming in sonar bathymetry, we present a benchmark study of adaptive beamforming techniques such as Low Complexity Adaptive (LCA) and Capon Minimum Variance (MVDR). Comparison with the Coherence Factor (CF) method is made as well. We use Delay-and-Sum (DAS) as a reference with various apodizations. We provide quantitative performance assessment based on the statistical distribution of the estimations with reference to the ground truth in different scenarios.

• Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter & Austeng, Andreas (2022). Underwater pipeline detection and localisation using multibeam echo sounder in a resolution limited case.
• Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes & Austeng, Andreas (2022). PhD project: Adaptive beamforming in underwater detection and estimation problems.
• Arnestad, Håvard; Gereb, Gabor; Birkenes Lønmo, Tor Inge; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2022). Sonar array beampattern bounds: tolerance analysis using interval arithmetic. Show summary

  The framework of interval arithmetic (IA) and its extension to complex numbers has in the last decade been applied as a tool for finding robust tolerance bounds of antenna arrays. The IA framework complements statistical methods, as inclusive upper and lower bounds of the beampattern are obtained directly, only assuming error bounds on specifically chosen array parameters. Recently, beampattern synthesis for sonar arrays subject to amplitude excitation errors has been extended from linear arrays with omnidirectional elements to non-linear arrays with directive elements. In this work, we demonstrate that the analysis can be developed further to include both amplitude and phase errors. Moreover, we account for error bounds in element position and orientation, thus representing a more comprehensive method for evaluating the worst-case performance due to uncertainty bounds in a multitude of design parameters. For this purpose, we have created an open-source MATLAB toolbox to calculate beampattern bounds for an array with bounded error tolerances. The toolbox features an object oriented library of interval classes and an interactive graphical user interface with easily configurable settings, where results for different interval representations are shown along with their corresponding bounds. The beampattern bounds of a sonar array is illustrated through an example.

View all works in Cristin