Research Of Multicomponents OBS Data Imagination Processing Methods

The OBS,which is the abbreviation for ocean bottom seismometer, is put on theseafloor to receive the seismic wave stimulated by the source point, which is usuallylocated near the sea surface. Then the OBS data is obtained via the seismic geometrysystem. As is known, the shear wave can not propagate in the sea water, so the usualmarine seismic prospecting just receives the P wave. But the OBS can receive boththe P and PS wave, because the ocean bottom seismometer contacts the seafloordirectly. Thus, it is possible to use the OBS seismic data to conduct multi-componentsocean seismic prospecting. PP wave and PS wave information, which is offered by theOBS seismic data, can be used to image the undersea layer. So the OBS data can usedto reveal more information under the sea. The arcitle mainly focused on theimagination processing of the OBS seismic data.The elastic wave equation staggered grid finite difference algorithm is used todecompose the p and s wave field in the isotropic media. In addition, the horizontal layeredmodels and the sea level fluctuation models are used to calculate the p and s wave.The coordinates of the OBS are usually not the same with what we scheduled forthe reason that it has been affected by the ocean current and other factors. So, thecoordinates of the OBS should be corrected before it is used for imaginationprocessing. The inverse time extrapolation method of the wave equation is used tocalculate the receiver’s location. The three dimensional speed-stress acoustic waveequation was derived, and then the difference formula was put forward with staggeredmesh difference method. In addition, the PML boundary condition was also derived.The coordinates scanning method was used to locate the results obtained using theinverse time extrapolation more precisely, and the CDP gathers’ linear moveoutcorrection results can be used to confirm if the coordinates calculated are right.The traces differ in amplitudes and its polarizaion direcitons with each other, because the OBS geometry fixed the receivers’ locations while the source pointschanged their’s, so the components rotation was used to solve the problem. The articleuse the three components received by the seismic detector, and finally to rotate the x,y and z component to the direciton of the sourec-receiver line, the perpendicular tothe source-receiver line and the vertical respectively. Because the real direciton of thecomponents are different from what we expected it to be, the direcitons should becorrected before the rotation was executed. The horizontal components rotation needtwice rotation according to the angle between the real and the supposed direction,while the vertical components roation just need once.The article used the method of combining the p and z component to eliminate thereverberation noise of the sea water. But it is not adopted to combine the twocomponent by summing directly because they differs greatly in ampliutdes. Thearticle calculated their normalization results using root mean square amplitudes, andthen calculated the scale factor of the z to p component by the time-changing windowweighting method. Multiply the z component by the factor, then combine the new zcomponent and p component, the multiwave noise will be eliminated effectively.The article uses the depth model to calculate the coordinates of the reflectionpoint, and propose a method of velocity analysis by calculating the statics correctionand normal moveout correction, and then use the result of the common reflectionpoint gathers to obtain the stack section.