John Sallas

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John Sallas
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SEG is honoring Jim Rickenbacker and John Sallas with the Fessenden Award for developing ground-force control for seismic vibrators, technology that resulted in deterministic source signatures and caused a step change improvement in vibrator seismic data quality. Ground-force control virtually eliminated the persistent problem of vibrator decoupling and led to a significant improvement in bandwidth. Jim Rickenbacker at Exxon Production Research Company developed and patented a system for controlling the peak force of a vibrator using the weighted-sum method for force control. This effort marked the first use of closed-loop vibrator force control in the industry. John Sallas, who began his work at GSI, was responsible for refining ideas and developing new methods for ground-force control that led to wide commercialization.

Biography Citation for the Reginald Fessenden Award

Contributed by Fred J. Bar

The Reginald Fessenden Award recognizes and honors a person who has made a significant technical contribution to exploration geophysics. In 1984, John Sallas published his work that established the most effective method for phase locking Vibroseis land energy sources. John’s method, now our industry’s standard, specified phase locking a vibrator’s computed ground force to the reference pilot sweep. His achievement in establishing this standard was a technical contribution of a caliber that has become identified with this prestigious award.

John earned his bachelor’s degree in 1973 at the University of Missouri at Rolla, and his master’s (1976) and doctorate (1982) at Southern Methodist University. All were in electrical engineering. Although his interests while earning those degrees ranged from electronics and microprocessors to digital signal processing and statistical communication theory, each degree plan contained a common denominator that is near and dear to his heart—optimal system control theory. While earning his master’s degree, John worked as a design engineer on vibrator test and control systems for Geophysical Services, Incorporated (GSI). So it was no accident that, after a brief absence during his doctoral studies, John was back at GSI in 1981 as project engineer and project manager for the development of its VCS V vibrator control system.

One can also appreciate how, during that same year, John took particular interest in a paper published in Geophysical Prospecting that recommended phase locking vibrators to reaction-mass acceleration. At that time, the industry’s standard was to phase lock to base plate acceleration. John and a colleague published a response to that paper in 1982 in which they offered computed ground force as the correct measure of the vibrator’s output to be phase locked to the pilot sweep. Although John and his colleague were later advised in an editor’s response to not “insist in making a trivial technical problem more difficult than necessary,” John persevered. At SEG’s 1982 Annual International Meeting, he presented a paper that not only explained fully why ground force was the answer, but also presented the results of downhole measurements that demonstrated its validity. John’s paper was published in GEOPHYSICS in 1984. Our industry quickly adopted the ground force method as its standard.

John Sallas has not rested on his laurels since setting our industry on the right track for Vibroseis source control. He continued to work at GSI on projects directed toward fundamental force amplitude control, ground roll and air-blast suppression, and the development of a downhole vibrator for cross borehole tomography. When Halliburton purchased GSI in 1989, he decided to stay in Dallas and formed his consulting company, geoMagic. As sole proprietor, he has remained very active in geophysics, providing technology to ARCO, Mobil, Western Geophysical, I/O, and Pelton. He is currently developing wider bandwidth, vibrator rotary servovalves for Atlas Fluid Controls. Outside the area of geophysical technology, John designs and manufactures medical equipment peripherals for telemetering digitized radiology data.

John has asked that numerous friends and colleagues be remembered for the critical support they gave during his work on the ground-force method. Among them are Cam Wason, John Bedenbender, Pete Embree, George Wood, and Dick Weber. I know that they join all of us, in sincerely congratulating John Sallas on receiving this well deserved recognition and thanks from our industry, the Reginald Fessenden Award.