MULTIPLE LOW FREQUENCY (MLF) ANTENNA

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MULTIPLE LOW FREQUENCY (MLF) ANTENNA
MLF antenna is one of the antennae used in GPR
survey. As name suggests the frequency of MLF can
be tuned to various frequencies. This animation
shows the efficiency of MLF in GPR data
collection on an undulating terrain using point
mode method.
Authors Almelu Mangamma V. Hebsur
M.Tech (Remote Sensing)?
Department of Civil Engineering
Indian Institute of Technology
Bombay
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Learning Objectives

• After interacting with this Learning Object, the
  user will be able to
• explain the point mode method of GPR data
  collection
• explain the relationship between arm length,
  frequency , and equivalent depth of penetration
  (i.e. two way travel time)?

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Definitions of the components
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1.Transmitter Antenna It is the electronics
which sends the Radar pulses into the earth at
particular central frequency 2.Receiver
Antenna It is the electronics which collects the
reflected radar pulses from the
subsurface. 3.Arm-Lengths Arms are a part of
antenna electronics. Their lengths decide the
frequencies and can be adjusted to obtain desired
central frequencies. 4.Two-way Travel Time It
is the time taken by the radar pulse to go into
the ground and come back. It is measured in terms
of nanoseconds(ns). It indirectly indicates the
Depth of penetration.
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Definitions of the components
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5. Point Mode Method In Point mode at every
point the data is collected manually. 6.
Radargram GPR data in an imagery form is
called radargram. It is the graph plot
between time(ns) and distance (m).
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Diagram 1
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One of the arms of the transmitter
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One of the arms of the receiver
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GPR data collection using Multiple Low Frequency
(MLF) antenna
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Diagram 2
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Set up of Multiple Low Frequency Antenna (MLF)
side view of transmitter and receiver
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Credits
Radio buttons (if any)/Drop down (if any)?
Play/pause
Restart
What will you learn
Lets Learn!
Interactivity options Sliders(IO1)? / Input
Boxes(IO2)? /Drop down(IO3)? (if any)?
Definitions
Diagram
Test your understanding (questionnaire)?
Animation Area
Lets Sum up (summary)?
Want to know more (Further Reading)?
Output result of interactivity (if any)?
Instructions/ Working area
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Questionnaire
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1) What are the components of MLF Antenna?
a)Transmitter b)Receiver
c)Antenna Arms d) All of them 2) What is
the relation between Length of antenna arms
and frequency of antenna? a) As the length
of antenna arms increases, Frequency
of antenna decreases. b) As the length of
antenna arms increases, Frequency of
antenna increases. c) As the length of
antenna arms increases, Frequency of
antenna remains same. d) As the length of
antenna arms decreases, Frequency of
antenna increases.
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Questionnaire
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3) What is the relation between Frequency and
Depth of penetration? a) As frequency
decreases, Depth of penetration
increases. b) As frequency decreases, Depth
of penetration decreases. c) As
frequency decreases, Depth of penetration
remains same. d) As frequency increases,
Depth of penetration increases. 4) What
is the advantage of MLF over other antennae?
a) Point mode data collection on Undulating
Terrain. b) Time mode data collection
c) Distance mode data collection d) All
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Summary

• The frequency decreases with increase in arm
  length.
• The equivalent depth of penetration (i.e.) two
  way travel time is the time taken for the signal
  to be transmitted to the ground and reflected
  back. For example if the two way travel time is
  400 ns it means that the signal took 200 ns to
  reach beneath the ground surface and 200 ns to
  reflect back.
• As frequency decreases, the equivalent depth of
  penetration increases.
• In point mode method, the GPR data is collected
  at each point manually. This method is useful for
  collecting GPR data for an undulating terrain.

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Links for further reading contd..

• Reference websites
• http//www.geophysical.com/
• http//en.wikipedia.org/wiki/GPR
• http//www.g-p-r.com/
• Books
• Jol, Harry. M., (2009), Ground Penetrating Radar
  
• Theory and Applications, 1st Ed., Elsevier
  Science.

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Links for further reading contd..

• Research papers
• Yelf. R.J. (2007). Application of Ground
  Penetrating Radar to Civil
• and Geotechnical Engineering. Electromagnetic
  Phenomena,Vol-
• 7,No-18
• Sato, M. (2001). Fundamentals of GPR data
  interpretation. Toholur
• University, Japan
• Davis, J.A. (1989). Ground-penetrating radar for
  high-resolution
• mapping of soil and rock stratigraphy,
  Geophysical Prospecting, 37 ,
• 531 - 551.