Impact of directional illumination control parameters on seismic signals
To improve quality of seismic signals, DICT (directional illumination control technique) of DVAS (the distributed vibrator array system) is developed. It explains DICT theory in seismic wave domain and states why DVAS can generate directional seismic wave with DICT. The property of directional seismic wave can be described with directional factor. From directional factor, some control parameters such as amount of vibrators, arrangement of DVAS and delay time play an important role in seismic wave directivity and reflected waves' SNR (signal signal-to-noise ratio). To study parameters of directional illumination system, receiving signals are simulated by numerical method. The results show that reflected wave' SNR can be improved with more vibrators and small space between adjacent source in the same line. When the amount and space of source are settled down, a long delay time can increase reflected wave' SNR in shallow lays and a short delay time can boost signal SNR in deep lays. It concludes that DICT is a better control method to achieve high SNR signals with proper parameters. Furthermore, it offers some rules on how to determine parameters.
Analysis of directional seismic signal based on phased-array vibrator system
When ambient noise is strong,seismic data signal-to-noise ratio(SNR)might still be low even if combination vibrators are used.To solve this problem we proposed to apply a phased-array vibrator system(PAVS),which can form a directional seismic wave.In theory,3-unit PAVS can make SNR of reflected waves increasing 6.53~9.54 dB than single vibrator,and 1.76~4.77dB than combination sources.In practice,field experiments were done with different sources in the same test field.The results show that a significant SNR improvement can be seen in reflected signals of PAVS than single source according to single shot records and horizontal stacking time sections.Of course,we also noticed that there is a little difference in time domain signals between seismic signals of PAVS and combination source.Furthermore,power spectrums of reflected wave signals are analyzed and we get some quantitative results:PAVS make SNR of reflected waves increasing 0.75~8.15 dB and 0.93~3.17dB at different traces respectively than single and combination sources.Mean SNR increases are 3.65dB and 2.02dB.It shows that the results from experiments are consistent with theoretical analysis.To evaluate PAVS and its effect on seismic signals,time sections from different sources were shown.It can be seen that directional illumination technology of PAVS is effective and superior to boost SNR of seismic signals than other routine sources.
Highly sensitive object location in tissue models with linear in-phase and anti-phase multi-element optical arrays in one and two dimensions.
Based upon previous observations of low-frequency photon diffusion waves within highly scattering tissue, this paper explores the "near-field" phenomena of such waves of approximately 10-cm wavelength with 200-MHz phase modulation equipment. Multiple-element source arrays consist of laser diode sources modulated at 180 degrees out of phase with respect to the other sources. The diffusing waves originating from the out-of-phase sources give, in the midplane, an amplitude null and a sharp phase transition. These may be observed in a highly scattering intralipid medium simulating the breast or brain (0.5% intralipid), 3-5 cm from the transmitting laser diodes. In the plane containing the array, there is a high sensitivity for a small volume of a hidden absorber (indocyanine green) deep within a highly scattering medium; 20 pmol in a volume of 70 microliters can be detected. Two-dimensional arrays consisting of four or more elements in two orthogonal planes give sensitivity on both axes similar to the one-dimensional array. Measurements show that in the presence of a light-absorbing object, the amplitude null and the interference plane becomes a curved surface which is deflected toward the heterogeneity. The degree of deflection is related to the volume and the absorption characteristics of the heterogeneity and provides detection of the heterogeneity, and thereby may provide localization information for the detection of small tumors within the human breast, or stroke volumes, aneurysms, and tumors in the human brain.