Processing Sequence – Radiometrics

A complete processing sequence for magnetic grids follows:

  1. Check grids (Utilities|Check Grids). Generates a report summarising the parameters for all grids in the input directory. Check that the projection and datum are the same for all grids. Check that there are no rotated grids (rot). Check that all grids have zero X and Y origin offsets (regX and regY).
  2. Generate a grid priority order – Utilities|Generate Priority Order. This will generate the default priority order based on cell and survey size. If required, manually edit the Priority Order File. Do this carefully – in order to maintain the one-to-one relationship between grids in the input directory and file names in the Priority Order File.
  3. Create a boundary view (optional) – Utilities|Create Boundary View. This will create a boundary view of each grid in the input directory. Use GridMerge|Merge to merge the individual boundary view grids into a composite Boundary View. 
  4. Trim grid edges (optional) – Grid Pre-Conditioning|Trim Grid Edges. Replaces the edges of grids with nulls.
  5. Trim grids to coastline – Grid Pre-Conditioning|Trim Grids To Coastline. Replaces offshore parts of grids with nulls. This is recommended for radiometric data where offshore data (which should be zero) can bias the analyses.
  6. Trim grid overlaps – Grid Pre-Conditioning|Trim Grid Overlaps. Trims grids such that they only overlap along their margins. After trimming the overlaps, use the Create Jpegs From Grids utility to generate jpegs and identify which grids may require further editing – see "Cleaning grids after Trim Grid Overlaps" in Trim Grid Overlaps. Use Boundary View (run on the overlap-trimmed grids) to see which portions of a particular grid are likely to contribute to the final merge. Then use Sub-Section a Grid to remove unwanted sections.  
  7. Get grid statistics – Utilities|Grid Statistics. Calculate and save statistics for each grid prior to grid conditioning. This will be used later if you choose to condition the grids.
  8. Condition the grids (optional) – Grid Pre-Conditioning|Condition Radiometric Grids. Grids are normalised to zero mean and unit standard deviation.
  9. Find the grid overlaps – Grid Levelling|Get Overlaps. Find the overlaps between grids and store them in a binary file – the Overlap Points File. The input grids are the conditioned grids from #8 above.
  10. Get relative shift/scale – Grid Levelling|Get Relative Shift/Scales. Use the binary file from #8 above to calculate the best shift and scale for each grid pair. The results are stored in the Overlap Grids File. This is an ASCII file which can be edited in a text editor to change the weights that are attached to each overlap when calculating the absolute shifts and scales (step #11 below).
  11. Get absolute shift/scale – Grid Levelling|Get Absolute Shift/Scale And Apply. Use the Overlap Grids File from #10 above to calculate the best shift and scale for each grid. If control lines were not used in #9 above, then this will require the nomination of a base grid to which all other grids are levelled. Applies the shift/scale corrections (to the output grids from #8 above) and writes the adjusted grids to the output directory.
  12. Find the grid overlaps (for tilting) – Grid Levelling|Get Overlaps. This time use the adjusted grids from #11 above to get the overlaps. Write the overlaps to a new Overlap Points File. 
  13. Tilt the grids – Grid Levelling|Get Grid Tilts And Apply.  If not satisfied with the results from #11 above, tilt the grids – using the overlaps generated in #12 above to get the best plane surface for each grid that, when subtracted, results in the best fit. Applies the tilt correction (to the output grids from #11 above) and saves the grids to a new directory.
  14. Merge grids – Grid Merge|Merge Grids. Merge the individual grids from #13 above into a composite grid. 
  15. Feather and merge grids – Grid Merge|Feather And Merge Grids. If satisfied with the results from #11 above, feather and merge the grids. 
  16. Adjust final grid for the base grid conditioning – Utilities|Shift/Scale Grid. If the grids were conditioned at #7 above, scale the merged grid by the standard deviation of the base grid then add the mean value. This adjusts the merged grid to the same level as the base grid.