The starting point for a relatively simple approach to data acquisition design can be found in the common focus point (CFP) philosophy, which describes seismic migration as a double focusing process. The migration output is presented as the combined result of focused source beams and focused detector beams for a given velocity model, revealing the potential amplitude accuracy and spatial resolution of a specific field geometry. In addition, any noise model can be fed into the input, and the subsequent beam‐forming operations can be applied to predict the potential noise suppression rate. The economical optimization comes from the possibility of balancing the source and detector efforts as well as the acquisition and processing efforts.
The acquisition geometry of a 3-D seismic survey should be designed in such a way that it allows high‐quality images and fulfills economical constraints. Focal source beams and focal detector beams are used to analyze and design field geometries. An attractive property is that the focal source and detector beams can be computed and evaluated separately. Seismic quality attributes such as resolution, noise suppression rate, angle‐averaged amplitude, and angle‐dependent amplitude information can be obtained efficiently from those beams. Examples confirm the theory that source and detector distributions may complement each other to achieve a high resolution. This important property can be used to design cost‐effective geometries. The acquisition design criteria for reliable amplitude versus ray parameter information turn out to be more stringent and may require a compromise in resolution.
Spatial resolution in medical ultrasound images is a key component in image quality and an important factor for clinical diagnosis. In early systems, the lateral resolution was optimal in the focus but rapidly decreased outside the focal region. Improvements have been found in, e.g., dynamic-receive beamforming, in which the entire image is focused in receive, but this requires complex processing of element data and is not applicable for mechanical scanning of single-element images. This paper exploits the concept of two-stage beamforming based on virtual source-receivers, which reduces the front-end computational load while maintaining a similar data rate and frame rate compared to dynamic-receive beamforming. We introduce frequency-wavenumber domain data processing to obtain fast second-stage data processing while having similarly high lateral resolution as dynamic-receive beamforming and processing in time-space domain. The technique is very suitable in combination with emerging technologies such as application-specific integrated circuits (ASICs), hand-held devices, and wireless data transfer. The suggested method consists of three steps. In the first step, single-focused RF line data are shifted in time to relocate the focal point to a new origin t' = 0, z' = 0. This new origin is considered as an array of virtual source/receiver pairs, as has been suggested previously in literature. In the second step, the dataset is efficiently processed in the wavenumber-frequency domain to form an image that is in focus throughout its entire depth. In the third step, the data shift is undone to obtain a correct depth axis in the image. The method has been tested first with a single-element scanning system and second in a tissue-mimicking phantom using a linear array. In both setups, the method resulted in a −6-dB lateral point spread function (PSF) which was constant over the entire depth range, and similar to dynamic-receive beamforming and synthetic aperture sequential beamforming. The signal-to-noise ratio increased by 6 dB in both the near field and far field. These results show that the second-stage processing algorithm effectively produces a focused image over the entire depth range from a single-focused ultrasound field.
Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Both economical and social requirements are pushing the industry to even higher levels of availability, reliability and safety of installations. The concept of predictive maintenance using permanent sensors that monitor the integrity of an installation is an interesting addition to the current method of periodic inspections reducing uncertainty and extending inspection intervals. Guided wave travel time tomography is a promising method to monitor the wall thickness quantitatively over large areas. Obviously the robustness and reliability of such a monitoring system is of paramount importance. Laboratory experiments have been carried out on a 10" pipe with a nominal wall thickness of 8 mm. Multiple, inline defects have been created with a realistic morphology. The depth of the defects was increased stepwise from 0.5 mm to 2 mm. Additionally the influences of the presence of liquid inside the pipe and surface roughness have been evaluated as well. Experimental results show that this method is capable of providing quantitative wall thickness information over a distance of 4 meter, with a sufficient accuracy such that results can be used for trending. The method has no problems imaging multiple defects.
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