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  3. EarthImager™ General Questions

How do I use Histogram Filtering to filter misfit data?

Follow the steps below to filter your data in EarthImager™.

Try it for yourself!

Use these sample exercise files to try the histogram filtering method. You can also request a free demo of EarthImager if you do not already have it installed on your PC.  

 

1. Start EarthImager™ and then set the parameters

2. Reset to Surface defaults to avoid any previous settings (see image below) (Tip: Make sure on each start of EarthImager™, that you reset to Surface defaults—especially if you're sharing EarthImager™ with others)

Screen Shot 2019-02-26 at 3.36.28 PM

 

3. Load your STG file (raw data)

4. You can turn on Remove Spikes by going to Settings > Initial Settings tab (see image below). (Note: A spike would typically exhibit itself as a singular extreme apparent resistivity value such as when the highest and lowest values are right next to each other in the raw data. These spikes will eventually filter out, but it is better to remove them up front.)

remove spikes

 

5. Leave all other settings the same as they are interrelated and edits will often cause artifacts

6. Run 1 model by pressing the green arrow button in the top left of the tool bar (see image below).

green arrow button

 

7. Right click on the inversion model (bottom most section) and select View Data Misfit Crossplot (see image below)

Screen Shot 2019-02-26 at 3.51.31 PM

 

8. You will likely see several outliers from the 1:1 line showing raw predicted vs measured

9. Right click again and select View Data Misfit Histogram data removal filter

10. Move the blue line left and right using the arrow keys on your keyboard. Keep your eye on the bottom of the window where Number of Data Removed = X is shown (see image below). Move the blue line to a point where X is ≤5%.

data removed

 

11. Click Remove Noisy Data button and the tool will then close

12. Run the model again by clicking the green arrow in the tool bar up top

13. Repeat this process until you see a tight fit on the cross plot and/or reasonable RMS compared to the first model. (For example, if your first model converged to 50% RMS, you will likely want to stop at ≤10% RMS for the final model. Very clean data is typically 5% or less.)

14. Save a JPEG of the cross plot

15. Save the Raw, Forward, and Inverted Resistivity Plot

16. In the main menu, go to View > Inverted Resistivity Section

17. Change Aspect Ratio to 1.0 unless you have space constraints.  A drop down bow is in the middle of the tool bar

18. Keep color contours to the range shown that are unique to each line. It is common to have wide ranges in resistivity from line to line so a fixed or normalized color scale will obscure the structure. 

19. Select the clip boundaries button (A small triangle symbol is over this button in the tool bar).

20. Use 1.0 as the aspect ratio unless you have steep topography included

21. Save the inverted model by right clicking and selecting file type