Transient Constant Area Surface and Downhole Wave Models - Measurement While Drilling Signal Analysis, Optimization and Design - page 118

4.3.6 Run 4. Very, very, very noisy environment.
Here, the noise level is increased further! The time delay between
transducers is 0.01 sec or 10 ms, as before. The S/N ratio is assumed to be 1/16,
which is very, very small. Excellent signal recovery is apparent in Figure 4.3e,
with blue and black signals being identical.
FUNCTION SIGNAL(T)
C MWD upward wave signal function
C Train of pulses, 0.5 sec width, 0.5 sec separation
C CASE 2. NARROW PULSE WIDTH (Considered in single xducer
method)
C Clearly see interference between upgoing and reflected pulses
A = 10.0
R = 100.0
SIGNAL = A*(TANH(R*(T-0.100))-TANH(R*(T-0.101)))/2.
RETURN
END
C
FUNCTION XNOISE(T)
C Mud pump noise function may also include reflected MWD
C signal, but it is not necessary to add the wave reflection to
C the total noise to demonstrate directional filtering.
C FRQPMP = Hertz freq of pump noise, propagates downward
PI = 3.14159
FRQPMP = 15.
C AMP = 0.25
AMP = 4. [Twice the above example, nothing else changed]
XNOISE = AMP*SIN(2.*PI*FRQPMP*T) + 0.0*SIGNAL(T)
RETURN
END
Figure 4.3e . Very, very, very noisy environment.