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.
ATTENUATING MULTIPLES FOR LOW SIGNAL-TO-NOISE RATIO SEISMIC DATA USING OPTIMAL BEAMFORMING
We present an optimal beamforming method and its application to attenuating multiple for low signal-to-noise (S/N) ratio seismic data,which is better than some popular techniques like f-k and Radon transformation.The key point of the method is updating the constraint in the optimal beamformer design by using adaptive beamformer with the quiescent weighted vector.The example of real data processing example shows that this optimal beamformer method has improved the minimum variance unbiased beamformer significantly in attenuating multiples for low folding and/or low S/N ratio data at small extra cost.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125