4.1.4.1. EM Data Type Functionality

4.1.4.1.1. Defining Transmitters

For FEM3Ddata, FEM3Dsounding, TEM3Ddata and TEM3Dsounding data objects, we can define transmitters for the survey. This functionality is accessed using the drop-down menu:

“data type menu” → Add Transmitters

4.1.4.1.1.1. Add Transmitters to 1D sounding

Here, the user may specify the transmitter locations and properties based on the data locations.

../../../../_images/addTransmitters.png

Select the object: “data type menu” → Add transmitters

  • Transmitter geometry

    • From File: Lets the user import a template geometry (XYZ coordinates) defining the transmitter coil.

    • Loop: Defines a simple loop transmitter with radius set by the user.

    • Dipole: Defines a dipole transmitter with moment set by the user (for EM1Dinversion)

  • Bearing

    • Calculate: Let GIFtools determine the bearing of survey lines. Assumes that the survey points are sorted in order of acquisition.

    • From data object: Bearing already supplied by the data object.

  • Offsets relative to bearing (XYZ)

    • Along-line offset: Distance along the survey lines between the data location and transmitter

    • Cross-line offset: Distance perpendicular to the survey lines between the data location and transmitter

    • Vertical offset: Elevation difference between the data location and transmitter. For the EM1Dsounding class, the offset is relative to the ground.

  • Rotation angles

    • Relative to bearing: Apply the rotation angles relative to the flight line orientation. Otherwise angles are relative to the Cartesian grid.

    • Pitch angle: Rotation angle about the wings of the bird. Positive angle moves the nose up, tail down.

    • Roll angle: Rotation angle about the length of the bird. Positive angle moves the left wing up, right wing down.

    • Yaw angle: Rotation angle about the XY plane. Positive angle rotates the bird clockwise.

../../../../_images/PitchRollYaw.png

Important

Make sure you have set i/o headers for the xyz-data locations. This functionality computes the transmitter locations based on the i/o headers.

4.1.4.1.1.2. Create Surface/Airborne Sources

Create inductive sources (loops) for surface or airborne EM surveys. This functionality is accessed using the drop-down menu:

“data type menu” → Add Transmitters → Create Surface/Airborne Sources

4.1.4.1.1.3. Create Single Inductive/Galvanic Source

Create a single inductive or galvanic source for all data in the object. This functionality is accessed using the drop-down menu:

“data type menu” → Add Transmitters → Create Single Inductive/Galvanic Source

4.1.4.1.2. Defining Receivers

For FEM3Dsounding and TEM3Dsounding data objects, we can define receivers for the survey. This functionality is accessed using the drop-down menu:

“data type menu” → Add Receivers

4.1.4.1.2.1. Add Receivers to 1D sounding

4.1.4.1.2.2. Create Surface/Airborne Receivers

Create loop receivers for surface or airborne EM surveys. This functionality is accessed using the drop-down menu:

“data type menu” → Add Transmitters → Create Surface/Airborne Receivers

4.1.4.1.3. Remove Transmitters

This functionality allows the user to remove transmitter information from the data object.

Select the object and the menu “data type menu” → Remove transmitters

4.1.4.1.4. Remove Receivers

This functionality allows the user to remove receiver information from the data object.

Select the object and the menu “data type menu” → Remove receivers

4.1.4.1.5. Waveform (TDEM objects only)

Here, we describe functionality related to defining, viewing and exporting waveforms for TEM data objects. This functionality is accessed through:

data type menu → Waveform

4.1.4.1.5.1. Create Exponent On - Ramp Off

Here, the user defines an exponential ramp-on linear ramp-off waveform and sets it to the selected TEM data object. This functionality is accessed through:

data type menu → Waveform → Create exponent on; ramp off

The parameters defining this waveform are as follows:

  • minimum time: the starting time for the waveform (in seconds). This time must be before your first time channel

  • maximum time: the end time for the waveform (in seconds). This time must be after your latest time channel

  • time = 0: the shut-off time

  • Number of segments: Number of intervals after t0 which use a different time-step length

  • Samples per segment: Number of linearly sampled points which define the time-step length in each segment

  • Exponent slope: The constant \(\alpha\) defining the exponential ramp on

  • Exponent time: The duration of the exponential ramp on

  • Number of exp samples: Number of data points, linearly sampled, defining the waveform during the exponential ramp on

  • Ramp time: The duration of the linear ramp off

  • Number of ramp samples: Number of data points, linearly sampled, defining the waveform during the linear ramp off

4.1.4.1.5.2. Create Step Off

Here, the user defines a step-off waveform and sets it to the selected TEM data object. This functionality is accessed through:

data type menu → Waveform → Create step off

The parameters defining this waveform are as follows:

  • minimum time: the starting time for the waveform (in seconds). This time must be before your first time channel

  • maximum time: the end time for the waveform (in seconds). This time must be after your latest time channel

  • time = 0: the shut-off time

  • Number of segments: Number of intervals after t0 which use a different time-step length

  • Samples per segment: Number of linearly sampled points which define the time-step length in each segment

4.1.4.1.5.3. Import a Waveform

Here, the user imports a custom waveform from a text file and sets it to the selected TEM data object. This functionality is accessed through:

data type menu → Waveform → Import (3D format)

4.1.4.1.5.4. View

Here, the user may look at the waveform assigned to the selected TEM data object. This functionality is accessed through:

data type menu → Waveform → View

4.1.4.1.5.5. Export for 1D

Here, the user may export the waveform in the format used by the EM1DTM code. This functionality is accessed through:

data type menu → Waveform → Export for 1D

4.1.4.1.5.6. Export for 3D

Here, the user may export the waveform in the format used by 3D codes. This functionality is accessed through:

data type menu → Waveform → Export for 3D