TY - CONF A1 - Grohmann, Maria A1 - Niederleithinger, Ernst A1 - Buske, S. T1 - Anwendung der Reverse-Time Migration auf Ultraschall-Echo-Daten in der zerstörungsfreien Prüfung N2 - Das Ultraschall-Echo-Verfahren ist eine klassische zerstörungsfreie Prüftechnik zur Bestimmung der Bauteilgeometrie sowie zur Lokalisierung von Einbauteilen und Fehlstellen. Der aktuelle Stand der Technik bei den Abbildungsverfahren ist die SAFT-Rekonstruktion (Synthetic Aperture Focusing Technique). Diese Gruppe von Verfahren weist u.a. Schwierigkeiten bei der Darstellung von steilen Grenzflächen auf und verarbeitet nur die primären Reflexionen am abzubildendem Objekt korrekt. Als Alternative werden seit einiger Zeit Migrationsmethoden aus dem Bereich der Geophysik evaluiert. Am Beispiel eines Stahlbetonfundamentes wurden in einer Vorarbeit die Kirchhoff-Migration und die Reverse-Time-Migration (RTM) getestet. Die strahlenbasierten Algorithmen der Kirchhoff-Migration und SAFT-Rekonstruktion sind eng miteinander verwandt. Die RTM hingegen basiert auf der numerischen Lösung der vollständigen Wellengleichung. Durch Kreuzkorrelation von zeitlich vorwärts- und rückwärtsmodellierten Wellenfeldern erzeugt die RTM die migrierte Abbildung. Für die Durchführung der RTM wurde ein 2D akustischer Code verwendet. Beide Migrationsmethoden wurden an auf Basis der akustischen Wellengleichung generierten synthetischen 2D-Daten sowie an realen Ultraschallmessdaten getestet. Letztere wurden mit Scherwellenprüfköpfen an der Fundamentplatte aufgenommen. Ein Vergleich der Migrationsergebnisse mit den Ergebnissen der SAFT-Rekonstruktion zeigte besonders für die RTM eine deutliche Verbesserung in der Abbildung der Bauteilgeometrie. Die Vorstudie an der Fundamentplatte lieferte somit den Nachweis, dass geophysikalische Migrationsverfahren auf reale Ultraschall-Messdaten anwendbar sind. Jedoch zeigten sich vereinzelt starke Artefakte und systembedingt Schwierigkeiten bei der Abbildung dreidimensionaler Strukturen. Nunmehr wird vom akustischen Code auf einen elastischen Code umgestellt, da die eigentlichen Ultraschallmessungen mit elastischen Wellen erfolgen. In einem ersten Schritt wurde dies mit dem Softwarepaket Madagascar realisiert und an einem einfachen 2D-Modell getestet. Dabei fanden verschiedene Quellanregungen Anwendung. Des Weiteren wurden zwei Abbildungsbedingungen evaluiert. Ergebnisse der Kreuzkorrelation der Verschiebungskomponenten der zeitlich vorwärts-und rückwärtsmodellierten Wellenfelder wurden mit Resultaten der Kreuzkorrelation der Skalar- und Vektorpotentiale beider Wellenfelder verglichen. T2 - 76. Jahrestagung der Deutschen Geophysikalischen Gesellschaft CY - Münster, Germany DA - 14.03.2016 KW - Ultrasonic echo technique KW - Synthetic aperture focusing technique (SAFT) KW - Reverse-time migration PY - 2016 AN - OPUS4-35840 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grohmann, Maria A1 - Müller, Sabine A1 - Niederleithinger, Ernst A1 - Sieber, S. T1 - Reverse time migration: introducing a new imaging technique for ultrasonic measurements in civil engineering JF - Near Surface Geophysics N2 - Ultrasonic echo testing is widely used in non-destructive testing in civil engineering to investigate concrete structures, to measure thickness, and to locate and characterise built-in components or inhomogeneities. Currently, synthetic aperture focusing techniques are mostly used for imaging. These algorithms are highly developed but have some limitations. For example, it is not possible to image the lower boundary of built-in components like tendon ducts or vertical reflectors. We adopted reverse time migration for non-destructive testing in civil engineering in order to improve the imaging of complicated structures in concrete. By using the entire wavefield, including waves reflected more than once, there are fewer limitations compared to synthetic aperture focusing technique algorithms. As a drawback, the required computation is significantly higher than that for the techniques currently used. Simulations for polyamide and concrete structures showed the potential for non-destructive testing. The simulations were followed by experiments at a polyamide specimen. Here, having acquired almost noise-free measurement data to test the algorithm, we were able to determine the shape and size of boreholes with sufficient accuracy. After these successful tests, we performed experiments at a reinforced concrete foundation slab. We obtained information from the data by reverse time migration, which was not accessible by traditional imaging. The imaging of the location and structure of the lower boundary of the concrete foundation slab was improved. Furthermore, vertical reflectors inside the slab were imaged clearly, and more flaws were found. It has been shown that reverse time migration is a step forward in ultrasonic testing in civil engineering. KW - Ultrasonic echo technique KW - Reverse time migration PY - 2017 DO - https://doi.org/10.3997/1873-0604.2017006 SN - 1569-4445 SN - 1873-0604 VL - 15 IS - 3 SP - 242 EP - 258 PB - Wiley AN - OPUS4-41921 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grohmann, Maria A1 - Niederleithinger, Ernst A1 - Buske, S. T1 - Geometry Determination of a Foundation Slab Using the Ultrasonic Echo Technique and Geophysical Migration Methods JF - Journal of Nondestructive Evaluation N2 - The ultrasonic echo technique is a frequently used method in non destructive testing for geometry Determination of concrete building elements. Important tasks are thickness measurements as well as the localization and characterization of built-in components and inhomogeneities. Currently mainly the synthetic aperture focusing family of techniques (SAFT) is used for imaging. These algorithms have difficulties in imaging steeply dipping interfaces and complicated structures such as steps and lower boundaries of voids. As an alternative two geophysical migration methods, pre-stack Kirchhoff depth migration and pre-stack Reversetimemigration (RTM)were tested in this paper at a reinforced concrete foundation slab. The slab consists of various reinforcement contents, different thicknesses and two pile heads. In a first step, both methods were evaluated with synthetic 2D data. In the second step, ultrasonic measurement data recorded with shear wave transducers on a line profile on the foundation slab were processed. The use of an automatic scanner simplified the measurements. A comparison of the geophysical migration results with those of SAFT shows, in particular for RTM, a significant improvement in the Imaging of the geometry of the foundation slab. Vertical borders were reconstructed and the location and structure of the lower boundary of the foundation slab were reproduced better. Limitations still exist in imaging the piles below the slab. KW - Kirchhoff migration KW - Ultrasonic echo technique KW - Synthetic aperture focusing technique (SAFT) KW - Reverse-time migration PY - 2016 DO - https://doi.org/10.1007/s10921-016-0334-z SN - 0195-9298 (Print) 1573-4862 (Online) VL - 2016/Band 1 IS - 35:1 SP - 1 EP - 13 PB - Springer CY - New York AN - OPUS4-35838 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Sieber, Sarah A1 - Niederleithinger, Ernst A1 - Grohmann, Maria T1 - Image denoising of ultrasonic echo data acquired on concrete N2 - Ultrasonic echo testing has become a common method in civil engineering for the investigation of concrete structures. The detection of inhomogeneities, reinforcing elements and the geometry of the object is required for quality assurance and Inspection. This assessment depends on the quality of ultrasonic images which can be improved by using Reverse Time Migration (RTM) rather than the standard method, Synthetic Aperture Focusing Technique (SAFT). Although RTM provides a better mapping of circular objects and (dipping) reflectors, the image is corrupted by migration noise. To suppress the image noise, we have tested various filter methods in the spatial domain, frequency domain as well as in the curvelet domain on ultrasonic RTM images. We found that either a spatial edge detection filter in combination with a lowpass filter (Laplacian of Gaussian filter) or two lowpass filter with different filter parameters (Difference of Gaussian filter) removed artefacts. An additional smoothing was obtained by applying the first generation curvelet transform after downsampling the image matrix and adding Gaussian noise. The proposed filter scheme is able to suppress RTM noise and enhance the image quality such that the objective interpretation of ultrasonic images for Quality assessment of concrete specimen is simplified. T2 - 76. Jahrestagung der Deutschen Geophysikalischen Gesellschaft CY - Münster, Germany DA - 14.03.2016 KW - Ultrasonic echo technique KW - Reverse-time migration KW - Image Denoising KW - Curvelet Transform PY - 2016 AN - OPUS4-35839 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -