Deghosting of Marine Seismic Data Using Dual Sensor Technology
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An inevitable phenomenon called the ghost reflection has always been a problem in marine seismic acquisition. The great contrast in acoustic properties over the air-water interface is causing an almost perfect reflection of the up going seismic signal that is reflected from the subsurface. Interference between the up-going and down-going ghost signal is altering the original shape of the signal, and results in notches at certain frequencies in the amplitude spectrum of the signal. The information contained within the vicinity of these frequencies are therefor highly degraded. The process of removing the effect of the ghost is called deghosting. There are different ways of eliminating the ghost, both on acquisition side and processing side. PGS is recording both pressure and vertical particle velocity of the wavefield. These measurements are complementary, and perfect deghosting can in theory be achieved by doing this. However, noise present in low frequencies in the measurements of the vertical particle velocity are causing problems. The purpose of this thesis is to develop a program that performs deghosting of the type of data that PGS acquire. Furthermore, we would like to find out how PGS are deghosting the low frequency end of the signal, where noise in present in the vertical particle velocity. The program that was developed is a simple implementation of equations derived by many in the past. The program was first tested on synthetic seismic data. The synthetic seismic data was generated using a finite difference method for solving the wave equation.The results indicate that pressure measurements are the only contributor to PGS' P-up in frequencies up to 25 Hz, and the major contributor up to 40 Hz.Further, noise related to weather has briefly been studied. Additional pressure due to ocean gravity waves are is not a problem with the present day recording technology. This is due to the low frequency nature of these waves. a It was found that a noise level increase can be expected when wind speed increase. The increase is almost the same for all frequencies.