Seismic data acquisition is a trade-off between cost and data quality subject to operational constraints. Due to budget limitations, 3D seismic acquisition usually does not have a dense spatial sampling in all dimensions. This causes artefacts in the processed images, velocity models, or other physical properties. However, we rely on, for example, the accurate images in determining the location of oil and gas-bearing geological structures, and the accurate elastic properties to characterise the reservoir. In this thesis, we propose new methods to improve existing technologies that can optimise marine seismic acquisition. In Part I, we aim at obtaining dense data in less time by improving the so-called blended seismic acquisition techniques. In Part II, we aim at obtaining an improved target illumination with a limited number of sources and receivers by developing an acquisition optimisation framework. @en

Landmines and Improvised Explosive Devices (IEDs) are among the most dangerous weapons found in (former) conflict areas. Many of them have only minimal or even no metal built in making it difficult to detect such devices via conventional metal detectors. Thus, alternative methods such as Ground Penetrating Radar (GPR) are deployed for this purpose. The field methodology of using GPR for the detection of buried objects generally includes varying degrees of inclination and height of the antenna in use. In this work, the influence of antenna inclination and height above ground is studied by using control studies with simple reflector geometries. The investigations shall provide more insights on the influence of these factors via measurements in controlled environments and numerical simulations. A comparison of the two is used to study the accuracy of numerical simulations of scenarios involving the detection of buried objects with GPR. The motivation hereby is the fact that gaining experimental data is generally very costly, time consuming and difficult to set up. Evaluations of the tested parameters showed the individual impact of each factor on the measured data. Height and inclination as well as exogenous factors, such as antenna orientation, subsurface structure and reflector geometry played a governing role influencing the measured data. The field measurements were successfully reproduced in numerical simulations. However, it is crucial to implement proper physical and geometrical parameters of the antenna, subsurface and reflector into the simulation environment to achieve realistic and reliable results. The findings of this thesis will be beneficial to implement more accurate numerical simulations in the future, which enables to study more complex, extensive and variable scenarios in a much faster, efficient and less costly manner.

This work determines whether the amount of frequency components present in the data can be reduced, whilst still retaining image quality, whereas most efforts in seismological research are done in reducing spatial sampling. It is shown using a PCA on the frequency spectra of several data sets that indeed a large redundancy in frequency content is present in onshore seismic data, and an attempt is made to generate a distribution of frequencies in order of importance. Given this redundancy in the frequency spectrum of onshore seismic data, it has been attempted to reconstruct the missing frequencies by applying the Fourier transformation iteratively to the data. However, this transform does not take spatial sampling into account, which is aimed at to compensate for the missing frequencies. Therefore it has been elected to use a linear Radon transformation instead, which keeps components which are connected in space-time connected in the transform domain. A CGNE scheme has been set up to reconstruct the data, which performs very well along the almost linear asymptots in the shot records, up to a reduction of 70% of frequency components. This scheme iteratively applies the linear Radon transform to a shot record, weighing the data in the transform domain with an amplitude based norm. The energy that was spread out due to aliasing because of the missing frequencies is refocused to the main reflectors, especially along the asymptots of the reflection hyperbola. Missing frequencies are reconstructed, up to a scaling factor, and band gaps of up to 6Hz get filled in very well. Next, it is attempted in this work to give quantitative quality metrics, to make comparison between seismic images easier and based on data, rather than subjective visual inspection. Treating migration as a black box, several quality metrics have been devised for the migrated sections: correlation to the ground truth, contrast within an image, average length of found lines, and local SNR. Contrast is not a very good metric to compare between images as its average across an image is almost constant with reduction percentage. The other parameters are good metrics and show a clear trend that the fewer frequency components present in the shot records, the worse the quality of the final image. An increase in deterioration of image quality is observed around 70% reduction, which is in correspondence with the earlier found value for the shot records.