Why Multi-Channel?

Because of an increased ability provided by multichannel seismic
exploration that discriminates useful signal from harmful noise, the
MASW method assures an increased resolution when extracting signal
in the midst of noise that can be anything from natural or cultural
activities (wind, thunder, traffic, etc.) to other types of inherent seismic
waves generated simultaneously (higher-mode surface waves, body
waves, bounced waves, etc.) (
Fig. 3).  The powerful multichannel
data-processing techniques that adopt various types of 2-D (time and
space) wavefield transformation methods have been fully utilized in
seismic exploration industry for more than half century.  In consequence,
overall field procedure for data acquisition and subsequent
data-processing step become highly effective and tolerant, rendering a
non-expert method.   

The multichannel seismic concept is analogous to an increased
accuracy in digital imaging technology in which color range and number
of pixels both play critical role (
Fig. 4).  An increase in the number of bits
allows a broader color range, while an increase in the number of pixels
allows a higher resolution.  When delineating the subsurface
information, the concept of number of channels plays a similar role to
those of the bit and pixel concepts.    
Advantages of the MASW Method

Unlike the shear-wave survey method that tries to measure directly shear-wave velocities—which is notoriously difficult because of difficulties in maintaining favorable signal-
to-noise ratio (S/N) during both data acquisition and processing stages—MASW is one of the easiest seismic methods that provides highly favorable and competent results.  
Data acquisition is significantly more tolerant in parameter selection than any other seismic methods because of the highest signal-to-noise ratio (S/N) easily achieved.  This
most favorable S/N is due to the fact that seismic surface waves are the strongest seismic waves generated that can travel much longer distance than body waves without
suffering from noise contamination (
Fig. 1).  
In comparison to a conventional drilling approach, it is fully implemented on the
ground surface (non-invasive), covers the subsurface continuously in a manner
similar to ground-penetrating radar (GPR), and provides more complete
coverage  (
Fig. 2).  
Fig. 1. Earthquake recording around the earth
showing strong surface waves.
Fig. 2.  Comparison of seismic survey and conventional drilling.
Back to What is MASW?
(Right) Fig. 3.  Illustration showing an MASW field survey and an
actual field record showing various types of seismic waves can be
distinguished.  Subsequent data analysis steps utilizing various types
of 2-D wavefield transformation method, longed used in seismic
characteristics of seismic waves.    

(Below) Fig. 4.  An analogy of the seismic multichannel approach to
digital imaging concepts of number of bits and pixels.  The more
number of bits and pixels available during image capturing process
will ensure the more accurate reproduction (i.e., higher resolution) of
reality.