Dr. S.K Steve Chang from Schlumberger Well Services, Texas, USA paid a visit to IACAS and gave two brilliant academic lectures for the researchers and students of IACAS and the students from the universities or institutes nearby.
The title of the first lecture was "Wave Propagation through Finely Layered Media: a Quasi-Static Solution". In the lecture, Dr. Steve Chang said that nearly all the solid medium on the earth were anisotropic. In order to analyze the elastic waves' transmission in the stratum, people usually regard the terrane as the overlay of many layered media. However, as the increasing of layered media, the echo and transmission on these layers was becoming more and more complex, which brought more and more difficulties for the analysis. So for solving this problem, the researchers put forward the "Quasi-Static Solution" method. Then he made a comparison between two methods -- "equivalent medium theory" and "quasi-static solution" and got the conclusion that the later method was superior to the former one in the precision of the results. At last, he illustrated how to apply the "quasi-static solution" in dealing with the problem of the elastic waves' transmission in the stratum and presented some experimental results.
The second lecture was titled "An Introduction to S-Transform for Time-Frequency Analysis". Dr. Steve Chang said S-Transform was the bridge between Short-Time Fourier Transform (STFT) and Wavelet Transform. S-Transform not only posed the advantages of these two methods but also had its unique features. For example, in S-Transmission, there was a movable time windows to analyze the signal like in STFT. On the other hand, the length of the time windows can be adjusted with the change of the frequency, which was the same as in Wavelet Transform. Besides these two points, the statistics of absolute phase can be reserved and the chosen of the Window Function were freer in S-Transform. In view of all these features, S-Transform had superiorities in the signal time-frequency analysis. In his lecture, Dr. Steve Chang presented some examples to show the audience how the S-Transmission apply in the signal processing in the field of physical geography, oceanography, atmospheric physics, mechanical engineering and so on.
After the 3-hour long lectures, a warm discussion on exploration of oil and gas reservoir and the contents of the lecture was followed. The audience said they benefited a lot from the lecture.
Brief Introduction of Steve Chang:
Dr. S.K. Steve Chang has been active in the oil industry during the past 30 years and has recently retired from Schlumberger. He joined the company in 1979 and his career progressed as a research scientist, research program leader, research department manager, product line manager, product development manager, vice president and general manager, global acoustic metier manager, and advisor to Merger and Acquisitions. During 2000-2004, he was in Beijing as vice president and general manager to build the Schlumberger Beijing Geoscience Center. Steve received his Ph.D. in Electrical Engineering and Computer Science from University of California, Berkeley. He has 19 US patents and more than 80 journal and conference papers in acoustics and electromagnetics. Steve was the 2007 SEG (Society of Exploration Geophysicists) Honorary Lecturer for South and East. He is currently an Asia Regional Coordinator for SEG and a member of Executive Committee of Chinese American Petroleum Association
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