Levelling—decorrugation and microlevelling
Contents
1. Decorrugate tool Apply the microlevelling process Choose Apply As the process proceeds INTREPID displays the flight lines with colours corresponding to the adjustment values being made to the field magdpoly Exit from the tool To exit from the Microlevel tool choose Quit from the File menu a Intrepid Microlevel File Filter Grid Format Interpolation Options Help Apply Show Zoom In Zoom Out Zoom Area 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Levelling decorrugation and microlevelling G14 10 lt 4 Back gt Grid the microlevelled result and compare it to the grid before decorrugation Library Help Top 1 Grid the microlevelled field From the Gridding Menu launch Gridding The INTREPID Gridding tool window appears From the albury dataset grid the field magfinal and save the grid as magfinal ers This field contains magnetic data which has been microlevelled Recall the instructions in Creating grids G07 for performing the Gridding operation Remember to place the grid outside the albury dataset directory Examine the grids before and after microlevelling Using the Visualisation tool examine the before and after grids magdpoly and magfinal See Visualisation tools G05 Note the absence of the linear corrugations in magfinal Intrepid Visualisation v4 1 MSI for Windows XP by TECHBASE1 File Line Display Point Di2. for the new field name Choose OK 5 Intrepid Microlevel lt p m gt Filter Grid Format Interpolation Options Hel Specify Dataset gt Open Input Grid Enter New Field Name Specify Corrected Signal magfinal Specify Corrections Output ions Save Options Quit Ok Cancel Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 9 Library Help Top Library Help Top lt 4 Back gt 5 Set the microlevelling filter parameters From the Filter menu choose Parameters The Filter Parameters box appears Set the Secondary filter along correction to 1600 and the Nominal Strike to 90 Accept the defaults for the Minimum and Maximum adjustment parameters and choose OK Quick review The secondary filter length depends upon whether you are using a levelled or corrections grid format For a levelled grid we recommend using the same value as the Decorrugation streak length The Minimum and Maximum adjustment parameters allow you to constrain the microlevelling adjustment to within these amplitude limits Filter Parameters Secondary filter along correction 1600 0 Nominal Strike Minimum adjustment 300 Maximum adjustment 300 Cancel Select the grid format From the Grid Format menu choose Levelled The format must be the same as the grid format chosen in the
3. INTREPID User Manual Levelling decorrugation and microlevelling G14 1 Library Help Top q Back gt Levelling decorrugation and microlevelling G14 Top After tie line levelling our data to remove non geological data artifacts we can now proceed to the final stage of processing of our airborne magnetic survey data We want to remove any remaining data artifacts which are not geological in origin but are the result of the data acquisition procedure This process is generally referred to as levelling We have already used a rigorous method called tie line levelling to remove most of the artifacts In this tutorial we use the INTREPID Decorrugation and MicroLevel tools to perform the final step in our processing sequence which is a type of filtering designed to remove any remaining linear short wavelength artifacts These artifacts are visible as corrugations in the gridded data This procedure is commonly referred to as microlevelling Context of this guided tour Library Help Top In the context of your data processing cycle microlevelling follows the magnetic diurnal correction GRF removal and tie line levelling This Guided Tour assumes you have already completed the Introduction to the Spreadsheet Editor G08 removed the GRF component G16 tie line levelled your data G19 and have a diurnally GRF corrected and tie line levelled field in your dataset ready for final processing Location of sample data for Gui
4. MG cycle Here is a step by step summary of the process 1 2 3 4 Use the Gridding tool to grid the tie line levelled field from the line dataset Use the Decorrugation tool to filter the grid and create a levelled grid Use the Microlevelling tool to use the levelled grid to adjust the tie line levelled field in the dataset and create a new microlevelled field Use the Gridding tool to grid the microlevelled field Finally use an appropriate visualisation tool to compare the tie line levelled grid to the microlevelled grid What you will do Flowchart Summary Library Help Top Process Outputs Decorrugation j Grid of Raw tool produces Gridof Data Grid of Corrections Corrections v Microlevelling tool applies Grid of corrected Corrections to Line field in Line data set dataset v Regrid using new corrected Field 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 5 Library Help Top Steps to follow Library Help Top lt 4 Back gt Launch the Project Manager Navigate to the directory install_path sample_data guided_tours intrepid datasets Create the input grid 2 Create a grid to be decorrugated You can skip this section if you do not wish to actually perform the gridding process We have provided a solution dat
5. aset for this section From the Gridding Menu launch Gridding The INTREPID Gridding tool window appears From the albury dataset grid the field magdpoly and save the grid as magdpolyl ers This field contains magnetic data which has been tie line levelled Recall the instructions in Creating grids G07 for performing the Gridding operation Remember to place the grid outside the albury dataset directory Decorrugation create a levelled grid 3 Launch the Decorrugate tool In the Project Manager select magdpoly ers From the Levelling Menu choose Decorrugation The INTREPID Decorrugate tool window appears Open the input grid If the grid has not opened automatically choose Open Input Grid from the File menu The Open Grid dialog box appears Select the grid magdpoly1 and choose Open INTREPID displays the grid in the Decorrugate window From the Grid Display menu change the display mode to Grid with Sun Angle You should be able to see linear artifacts corrugations running across the dataset These are the features we want to remove ee Help File Filter Grid Output Grid Display Extrapolator Polygon Help Open Input Grid Specify Output Grid z Measure m Load Options 0 0000000 Save Options Quit Apply Show Zoomin l 5 Specify the output grid From the File menu choose Specify Output Grid The Save Output Grid dialog box appears Type dec
6. ded Tours We provide two complete sets of sample datasets one in INTREPID format and one in Geosoft format INTREPID works equally well with both formats When you want to open a dataset navigate to the directory containing the required data format Where install_path is the path of your INTREPID installation the project directories for the Guided Tours sample data are install_path sample_data guided_tours intrepid_datasets and install_path sample_data guided_tours geosoft_datasets For example if INTREPID is installed in C Program Files Intrepid Intrepid4 5 nnn then you can find the INTREPID format sample data at C Program Files Intrepid Intrepid4 5 nnn sample_data guided_tours intrepid_ datasets This is the default location for the sample data If you have installed INTREPID normally the data resides there If you have installed INTREPID elsewhere the exercises will work just as well Just use the appropriate pathnames For more information about installing the sample data see Sample datasets installing locating naming in INTREPID Guided Tours Introduction G01 For a more detailed description of INTREPID datasets see Introduction to the INTREPID database G20 For even more detail see INTREPID database file and data structures R05 Location of sample data for CookBooks Right next to the Guided tours data is a rich set of more exotic geophysics datasets and grids already prepared for the cookbook training s
7. essions A casual user might 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 2 Library Help Top 4 Back gt also gain some trial and error insights into the capbilities of the software just by testing the Project Manger s ability to preview and describe the attributes of each of the cookbook datasets Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 3 Library Help Top 4 Back gt Overview Our aim in processing aeromagnetic data is to produce a time independent map of local anomalies with the Earth s regional magnetic field removed and with artifacts caused by errors in the acquisition process removed The effectiveness of tie line levelling is limited by the number of tielines and thus crossover points which are collected during a survey The wavelength of non geological features which can be removed using tie line levelling is limited by the distance between tie lines Before the advent of affordable imaging processing software and accurate GPS navigation magnetic survey data was routinely contoured as a final product At this level of data presentation tie line levelling was generally sufficient to remove artifacts from the line data Routine enhanced imaging processing brought about the need to remove remaining residual errors after standard processi
8. id changes to the line dataset using the Microlevelling tool it only makes adjustments to areas covered by the levelled grid Alternatively we have added a subsection block into the batch language including the new V5 0 protobuf form to support this funtion directly in this tool Q Can I use rotated grids in this tool A Yes The Decorrugation tool can only decorrugate E W or N S oriented features grid rows or columns and so for survey lines flown at an angle it is necessary to rotate the grid before decorrugating it The Microlevelling tool can handle rotated levelled grids Q Do these tools only work with magnetic data A No Decorrugation and Microlevelling can be applied to different types of data including digital terrain models radiometrics and EM data However there is only support for one component of the signal at a time We have not tackled upgrading these tools for vector tensor use directly Library Help Top 2012 Intrepid Geophysics 4 Back gt
9. ment 30 0 Select the grid output mode TT From the Grid Output menu choose Levelled HighPass Tolerance _0 0100 Decorrugate along columns Decorrugate along rows Note you can output either a Levelled or a O NETEN Corrections grid A levelled grid is easier to ali i pai ites 6 E T examine visually before you proceed to microlevelling Otherwise the choice is not important OK Cancel Apply the decorrugation filters Choose Apply The process proceeds When completed the levelled grid displays in in the Decorrugate window Examine the results If you want to examine just the corrcetions repeat 7 amp 8 again Exit from the tool To exit from the Decorrugate tool choose Quit from the File menu 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 7 Library Help Top 4 Back gt en intrepid Decorrugate File Filter Grid Output Grid Display Extrapolator Polygon Help Measure m o d000000 Apply Show Zoomin ZoomOut B Zoom Area C Measure Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 8 Library Help Top 4 Back gt Microlevelling apply the levelled grid adjustments to the line data 1 Launch the Microlevelling tool From the Project Manager Levelling Menu launch MicroLevelling The INTREPID Microlevel tool
10. ng and tie line levelling Micro levelling is a general term that fulfils this requirement The INTREPID implementation of microlevelling is a two stage operation beginning with a grid created from the tie line levelled data The Decorrugation tool uses filtering to remove corrugations from a grid and creates a grid without corrugations which we call a levelled grid You can tune the filter parameters to remove corrugations of a certain width and length thus minimising the loss of geological information from your dataset e The Microlevelling tool applies corrections to a line dataset based upon the values in the levelled grid Each data point is adjusted according to the value of the nearest levelled grid cell value The following illustration shows a grid created from some data before microlevelling and one created after the data was microlevelled Intrepid Flight Path Editor 3 1d I gt Intrepid Flight Path Editor 3 1d Display Grid Display Window Help File Edit Line Display Point Display Grid Display Window Help Corrugation Corrugation removed Before microlevelling After microlevelling Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 4 Library Help Top The GDMG cycle lt 4 Back gt The steps required to obtain a microlevelled data field comprise the Gridding Decorrugation Microlevelling Gridding GD
11. orr and choose Save 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 6 Library Help Top Library Help Top 6 8 lt 4 Back gt Set the decorrugation filter parameters Quick review The Decorrugation tool is designed to remove features with specific characteristics Therefore you should select filter parameters that remove corrugations only and do not remove geophysical information A good rule of thumb is to make the filter width at least twice the aquisition line spacing and the filter length between 5 and 10 times the line spacing In practice you may find that decorrugations are significantly shorter than this if they are caused by for exampe aircraft clearance variations The albury dataset has an average acquisition line spacing of about 200m anda tie line spacing of 1000 and 2000m Therefore as a starting point we can set the Streak Width to 600m and the Min Streak Length to 1600m From the Filter menu choose Parameters The Filter Parameters box appears Set the Min Streak length to 1600 and the Streak width to 600 Accept the defaults for the other parameters and choose OK The decorrugator can only operate in one of two directions either NS grid columns or EW Filter Parameters grid rows For this dataset we decorrugate Min Streak length _ 1600 0 along grid rows so accept the default setting j Streak width Minimum adjust
12. splay Grid Display Polygon Display Window Help AAR BF Intrepid Visualisation v4 1 MSI for Windows XP by TECHBASE1 File Line Display Point Display Grid Display Polygon Display Window Help G magdpoly LINE E PNT N POLY Signal g x N Y Line gt Zoom In am Zoom Previous Bf Mouse Mode C Query 1 C Zoom or Trace 2012 Intrepid Geophysics Se G magfinal yi LINE PNT YW POLY Ne Signal x fe Nae Line FID1 nS FiD2 Dist m Be he Z Value og Km Zoom In Ne Zoom Previous N E Mouse Mode a E Query C Zoom or Trace 4 Back gt INTREPID User Manual Levelling decorrugation and microlevelling G14 11 Library Help Top 4 Back gt Key points for this guided tour In this guided tour you have used the Decorrugation Microlevelling and Gridding tools to Create a levelled grid with corrugations removed Decorrugation Use the levelled grid to create a new microlevelled field in the line dataset Microlevelling Create a microlevelled grid from the microlevelled field Gridding Congratulations You have successfully processed the magnetic data from the albury airborne geophysical dataset Frequently Asked Questions Q Can I apply these methods to a subsection of a grid A Yes You can use the Subsection tool to define a grid of just the required area You can then decorrugate this smaller grid When you apply the levelled gr
13. window appears 2 Open the input dataset and field From the File menu choose Specify Dataset Open Original Signal The Select Database dialog box appears Select the dataset albury DIR and choose Open The Select Signal Field dialog box appears Select magdpoly from the list of dataset fields and choose OK If you already have X Y and Linetype assigned as INTREPID alises an information box appears Choose OK Load Signal Filter Specify Dataset gt Open Original Signal Open Input Grid Open Input X peep Necro Dee Loti Grid Format Interpolation Options Help l Specify Corrected Signal EIo Specify Corrections Output Open Input LineType Apply Load Options Show l j Save Options Quit j ebagoola_A DIR E euler _ss ebagoola_B DIR polyA J ebagoola_F DIR E polyB C ebagoola_5 DIR ebagoola_5T DIR polyB albury DIR euler_s DIR ile name Jalbury DIR iles of type Any Table l Open as read only 3 Select the input grid From the File menu choose Open Input Grid The Open Grid dialog box appears Select the grid decorr which you created earlier and choose Open INTREPID displays the grid in the Microlevel window 4 Specify the output field name From the File menu choose Specify Corrected Signal The Save Corrected Signal dialog box appears Click in the Enter New Field Name text box and delete levelledzZ Now type magfinal
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