Summary
This document describes how to perform standard threshold target picking using the Blakely Peak Detector Algorithm (Blakely, 1986).
Pre-requisites
Target picking
Configure the picking function
- Starting from the Pick & Invert tab.
- Open the Drag & Drop Functions menu button, f(x).
- From the Target Pick node, drag the Detect Targ function into the target picking flow.
- Select the New button to configure a target picker.
- Following the video below enter each piece of information.
![Jekyll](images/pages/btfield_target_picking/btfield_target_picking_config.gif)
Create a noise polygon
BTField requires that the user creates a noise polygon before running a target picker. The user will be warned if the picking threshold is too close to the noise estimated from the noise polygon. Follow the steps in the video to create a noise polygon. Complete the polygon by pressing the return key.
![Jekyll](images/pages/btfield_target_picking/btfield_target_picking_noise.gif)
The user may also want to record the value of the noise within the noise polygon. This can be done by right-clicking on the polygon and selecting Copy Noise Values.
![Jekyll](images/pages/btfield_target_picking/btfield_target_picking_noise_values.gif)
Run the picking function
Start the target picker by pressing the Auto-pick button. BTField may take a while to respond for datasets where many targets are found. Please wait till it’s finished. Note: the video below has had time clipped away while waiting for the taret picker to complete processing.
![Jekyll](images/pages/btfield_target_picking/btfield_target_picking_result.gif)
Parameter definitions
![Jekyll](images/pages/btfield_target_picking/btfield_target_picking_parameters.png)
- Cfg: This shows the name of the configured picker. Each time you press New and save a new picker, it’s name will appear in this dropbox.
- Name: User may enter or edit the name of a configured picking function.
- ln: Select the data state to pick on. This is typically selected to be data state -a.
- Worst case threshold from Detection Modeller: This is the threshold at which to pick targets.
- Cell Radius: Search radius for any point that is a maximum within a circle of radius is selected as a pre-merge target.
- Grid Sep X: Grid spacing in the x-direction.
- Grid Sep Y: Grid spacing in the y-direction.
- Blanking: Distance of a grid node from a data point at which to assign a null value to the grid.
- Merge Dist: Minimum distance allowed for neighboring picks. Picks within this distance of a pick with greater amplitude will be removed.
- Positive peaks: Toggle to allow picking of both negative and positive peaks.
- for off-time: The time channel at which the threshold will be applied.
- SUM: For advanced configuration of summed and specialized target picking channels.
- Tx Cmp: Tx component to use.
- Rx Cmp: Rx component to use.
- Set Tx-Rx pairs: Allows user to select which Tx-Rx pairs will be used for target picking.
References
Blakely, R. J., and Simpson, R.W., 1986, Locating edges of source bodies from magnetic or gravity anomalies: Geophysics, v. 51, p. 1494-1498.