Stories from the Field,Fundamental Questions and Solutions - Measurement While Drilling Signal Analysis, Optimization and Design - page 43

Figure 1.6b. Low-frequency (10 Hz) long wind tunnel data.
Figure 1.6c. Low-frequency (10 Hz) signal recovery.
Complementary results obtained at 45 Hz are shown in Figures 1.6d,e.
The left diagram of Figure 1.6d is clearly not sinusoidal and provides evidence
of nonlinear harmonics. Their magnitudes are measured from frequency domain
analysis and efforts are made to determine their physical origin. Again, we have
successfully extracted the MWD signal from a noisy environment. Our work
showed that transducer spacings of 10% of a wavelength sufficed for signal
extraction. At the present, not all noise sources are included in our modeling
efforts. Vibration and other sound mechanisms will be included in future work.
Figure 1.6d. High-frequency (45 Hz) long wind tunnel data.