Ground-penetrating radar
========================

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Theory
------

(text)

For further details, see script of lecture *Angewandte Geophysik II*
from Georg Kaufmann.

Material properties
-------------------

-  electrical conductivity :math:`\sigma_e` [:math:`\Omega`\ m].
-  dielectric permittivity :math:`\epsilon_r` [-].

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Instrument(s)
-------------

1. **SIR4000:** Processing unit

.. figure:: images/GSSI_SIR4000.jpg
   :alt: *SIR4000*, photo GSSI

   *SIR4000*, photo GSSI

2. **100 MHz-antenna:** monostatic antenna

.. figure:: images/GSSI_100MHz.jpg
   :alt: *100 MHz mono-static antenna*, photo GSSI

   *100 MHz mono-static antenna*, photo GSSI

3. **200 MHz:** bi-static antenna

.. figure:: images/GSSI_200MHz.jpg
   :alt: *200 MHz bi-static antenna*, photo GSSI

   *200 MHz bi-static antenna*, photo GSSI

`Homepage of manufacturer <https://www.geophysical.com/>`__

Assembly
--------

**Important:** Do not insert battery, until all cables are connected!

-  Lay out antenna, attach survey wheel (possibly the metal clamps need
   to be re-attached).

-  Connect survey-wheel cable to antenna.

-  Connect antenna cable, one side to antenna, the other side to
   SIR4000.

-  Insert battery into SIR4000 unit and switch on.

Configuration
-------------

-  Choose antenna type from menu below.

-  Start new survey / project. Define name (and storage place).

-  …

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Field measurement
-----------------

**Important:** Two persons are needed!

-  Calibrate the survey wheel, if you are not sure is the recorded
   distance is ok.

-  One person drags the antenna. Make slow, gentle progress, antenna
   should not be tilted and should not jump. If the SIR4000 unit beeps,
   the speed is to high for data processing.

-  One person carries the SIR4000 unit with shoulder harness. The
   antenna cable should **not** touch the ground.

-  The screen on the SIR4000 unit displays a *pseudo-moving profile*,
   with distance running …

-  **start** profile measurement by pressing the green button. The
   screen turns blue, and once the antenna is moved, the distance bar
   starts moving. The actual profile record is displayed as file number
   on top.

-  **stop** profile recording by pressing the red button long (longer
   than 3 seconds). The unit should ask you, if you want to save the
   profile. Once you press *ok*, the unit directly initiates the new
   recording mode.

Data download
-------------

Use USB stick to download data. Insert USB stick into SIR4000 unit. Go
to menu *Playback*. Choose project, then either mark single profiles, or
all profiles, and press *copy to USB*.

Post processing
---------------

**Important:** Package *Reflexw* is used for post processing!

-  Open *Reflexw*.

1. The program asks for a directory, where it can find data. In this
   directory (which you can define), there should be a folder **ASCII**.
   In this folder, the files downloaded from the *SIR4000* unit should
   be stored (``*.DZX`` and ``*.DZT``).

2. Other folders will be created by *Reflexw*, if they do not exist
   (**ROHDATA**, **PROCDATA**, **LINEDATA**, **MODEL**).

-  **Import:**

1. Open the *dataimport* window (either under File or import button).

2. As format specification, use *RADAN* with *new 32 bit floating
   point*.

3. As filename specification, choose *original name*.

4. If topography and coordinates are read in, under *update
   traceheaders*, choose *use data folder* and then *WKSTRANS-GPS* from
   dropdown menu.

5. Press *Convert to Reflexw*, then you will be prompted for a filename
   to import.

-  **Filter:**

1. STATIC CORRECTION: time cut

2. 1D: dewow (15 ns)

3. 2D: background removal

4. GAIN: manual gain (y)

5. 2D: stack traces

6. …

-  **Export:**

1. File -> export: *ASCII-4COLUMS*, choose *traceheader coordinates*,
   then filepath to *procdata*, and press *start*.

Georeferencing
--------------

We need to add coordinates and elevations for all traces to achieve a
proper geo-referenced data file. This coordinate information needs to be
added **before** we process the GPR profile, as the topographical
information influences the processing.

See section on **coordinate proesssing**!