E4D User Guide

Travel-time Methods Survey File

The input survey file provides the locations of sensors and describes how sensors are used to produce measurements. In inverse run modes, the input survey file also lists measurement values and standard deviations.

An output survey file with the extension of <.srv> is created during Forward Modeling that is named after the conductivity file used in the forward simulation. The simulated measurements are entered in place of the observed measurements. This file is meant to aid synthetic imaging studies, whereby simulated data collected within a known conductivity distribution are used to investigate aspects of the inversion. The standard deviation of each measurement is entered as 5% of the travel time magnitude as a placeholder, but noise is not added to the simulated data.

See File Syntax Rules for specific details.

Variable Name Description
n_sens

(int)

 n_sens is the number of sensors.
e_ind   ex      ey      ez       e_flag

(int)     (real)  (real)  (real)  (int)

repeat repeat for n_sens


e_ind is the sensor number.

ex, ey and ez are the coordinate positions of the sensor.

e_flag is the boundary flag for the sensor.

e_flag = 0

sensor is below the surface

e_flag = 1

sensor is on the surface
n_meas

(int)

 n_sens is the number of measurements.
m_ind  a     b     v_obs   v_std

(int)     (int) (int) (real)    (real)

repeat repeat for n_meas


m_ind is the measurement number.

a is the sensor index of the source sensor.

b is the sensor index of the receiver sensor.

v_obs is the observed travel-time*.

v_std is the standard deviation of v_obs*.

*For forward modeling, v_obs and v_std are not used, however a value must be entered.
Forward TT Simulation Modeling Example 

16  number of sensors
1 -7.5 0 -6  1      e_ind, x, y, z, borehole sensor  values for sensor 1
2 -7.5 0 -10 1      e_ind, x, y, z, borehole sensor  values for sensor 2
3 -7.5 0 -14 1      e_ind, x, y, z,
...
64  number of measurements
1 1 10 10.0 1.0     m_ind a b v_obs v_std
2 1 11 10.0 1.0     note: the v_obs and v_std are arbitrary placeholders in this example
...
Forward TT Modeling Output Example 

16  number of sensors
1 -7.5 0 -6  1      e_ind, x, y, z, borehole sensor  values for sensor 1
2 -7.5 0 -10 1      e_ind, x, y, z, borehole sensor  values for sensor 2
3 -7.5 0 -14 1      e_ind, x, y, z,
...
64  number of measurements
1 1 9  16.054   0.8127     m_ind a b v_obs v_std
2 1 10 16.603   0.84013    note: simulated measurement values, v_std=0.05*|v_obs|
3 1 11 18.692   0.94459
...
Inverse TT Modeling Input Example 

16  number of sensors
1 -7.5 0 -6  1      e_ind, x, y, z, borehole sensor  values for sensor 1
2 -7.5 0 -10 1      e_ind, x, y, z, borehole sensor  values for sensor 2
3 -7.5 0 -14 1      e_ind, x, y, z,
...
64  number of measurements
1 1 9  16.054   0.32108     m_ind a b v_obs v_std
2 1 10 16.603   0.33206     note: v_std is determined from field data errors, in this case 0.02*|v_obs|
3 1 11 18.692   0.37384
...