Deyan Draganov, a postdoctoral fellow at Delft University, is internationally known for his excellent research and publications in wave propagation and seismic interferometry (SI). He wrote his master’s and PhD theses on SI, has published 10 papers in international and/or peer-reviewed journals (including TLE, Geophysics, Geophysical Prospecting, JASA, and Geophysical Research Letters), has 52 peer-reviewed abstracts at international conferences, and has co-edited an SEG book on SI. In terms of service to SEG, he has been an Associate Editor of Geophysics since 2005 and has co-edited a supplement of Geophysics on SI. He received the award for best student poster paper at SEG’s 2003 Annual Meeting.
Biography Citation for the J. Clarence Karcher Award
Contributed by Kees Wapenaar
It is a great privilege to write this citation for Deyan Draganov, who is receiving the J. Clarence Karcher Award for his pioneering work on retrieving the Earth’s reflection response from ambient noise by seismic interferometry (SI). Deyan is a collector of rare vinyl records, so he was already interested in noise before he started this research. The main challenge of listening to vinyl records is to hear music behind the noise. Similarly, noise in seismic data is traditionally considered a nuisance that needs to be removed to restore the seismic signal. Deyan goes a significant step further; he does not separate noise from signal but he uses the noise itself and turns it into signal. This is like listening to a vinyl record with noise only and hearing a song of the Choir of the Bulgarian Riviera. It sounds like magic, but Deyan can make it happen.
Imagine a distribution of uncorrelated noise sources in the subsurface. One might think that the wavefield recorded at the surface is completely diffuse, but it is not. While propagating from the sources to the receivers, the noise field receives an imprint of the geology. Noise responses at neighboring receivers have been imprinted by the same geology and are therefore not uncorrelated. As a matter of fact, by taking the crosscorrelation of the noise recorded at two receivers, one obtains the response that would be recorded by one of the receivers if there were a source at the position of the other. In other words, the crosscorrelation of passive noise observations gives the reflection response of an impulsive source at the surface, similar to the response of an active seismic experiment with, e.g., a dynamite source.
The possibility of turning noise into signal was shown by Claerbout in 1968 for a horizontally layered medium. Between 1968 and 2000, there were several tests with real data, some more successful than others. The research got full momentum around 2001, when several groups in different disciplines obtained promising results (e.g., with diffuse ultrasonic waves in enclosures and with ocean-generated surface waves in regional seismology). Deyan has been involved in these developments since 2001. For his master’s thesis, he tested a generalization of the theory on numerically modeled data. In his PhD thesis (2007), he discusses SI for acoustic, elastodynamic and electromagnetic waves, proposes theoretical extensions, and applies SI to ultrasonic transmission measurements and to ambient seismic noise, recorded in a desert area in the Middle East. In a recent Letter in Geophysics (2009), he retrieves a pseudo 3D reflection image from ambient noise recorded by Shell in the northeastern part of the Sirte basin, Libya. The main hurdle was the separation of the low-amplitude body-wave noise from the overwhelming surface wave noise. This is like listening to a vinyl noise record in a soccer stadium and picking up a song from the noise behind the sound of vuvuzelas.
Deyan’s pioneering contributions have been recognized by the geophysical community via his 10 journal publications and his numerous conference presentations. This has led to many invitations and attractive job offers. Fortunately, Deyan has chosen for an academic career. In 2007 he received a prestigious VENI postdoc grant for top talents from NWO (the Netherlands Organization for Scientific Research) and he is now himself a mentor for younger scientists. Receiving the J. Clarence Karcher Award is a milestone which marks his significant achievements to date and the excellent scientific career that lies ahead of him.