Fixing the Herringbone Effect Using Time Constant Delay Correction
Introduction
All Geomar programs include a Time Constant Delay correction for XYZ files that contain a time stamp for each reading. The software calculates the instrument speed at each measurement point and adjusts the recorded position to compensate for system delay. Figure 1 shows the herringbone effect (before correction) and the corrected result after applying Time Constant Delay correction.
This approach is more accurate than typical “de-herringboning” algorithms because it:
Figure 1
preserves all original data,
does not smooth or distort anomalies,
retains even very small, high-frequency features.
Click the images below for a larger view.
Determining the Time Constant (Sensor + GPS System)
Although the time constant of the geophysical instrument may be known, the effective time constant of the system depends on both:
After applying the correct value, a linear anomaly (e.g., a pipe) should appear continuous and free of the herringbone effect.
Because this evaluation typically involves generating and reviewing gridded maps, the process can be time-consuming. However,it only needs to be performed once for a given combination of sensor and positioning system.
Procedure
1. Prepare the XYZ File
Before applying the correction:
Generate an XYZ file for the dataset (correction is applied to XYZ files only).
Ensure the file .
2. Open the Correction Tool
Figure 2
The Time Constant Delay correction is available in the menu:
Convert Data Files → Correct Time Constant Delay in XYZ File (Figure 2).
Selecting this option opens the Correct Time Constant Delay window (Figure 3).
Note: Files are referred to as “XYZ” for simplicity, but may use other extensions such as DAT or TXT.
3. Select Input and Output Files
Before applying the correction:
Click Input File and select the original XYZ file.
Click Output File and specify the corrected file.
By default, the program suggests the input file name with a C prefix. You may accept this or provide a custom name.
Once both files are selected, the Proceed button becomes active.
Figure 3
4. Set Parameters
System Time Constant
Default value depends on the instrument (e.g., 0.55 s for Geonics EM31).
Adjustable range: 0 to 2 seconds.
Use a value determined for your specific system.
Maximum Gap Between Readings
Defines the maximum time interval (in seconds) for data to be treated as continuous.
If the gap exceeds this value, the next reading is treated as the start of a new line or dataset segment.
Recommended value: 3–5× the GPS update interval.
Coordinates in XYZ File
Select the coordinate type used in the input file:
UTM (linear units)
Geodetic (Longitude/Latitude in degrees)
The output file will retain the same coordinate type.
5. Create the Corrected XYZ File
Figure 4
After setting all parameters:
Click Proceed.
The program begins analyzing the input file (“Analyzing File” message is displayed).
Corrections are calculated for each station based on the instantaneous velocity of the system.
A progress bar indicates processing status (Figure 4).
Important Notes
If the input file does not contain time stamps, a warning message will appear and processing will pause until confirmed.
Always apply corrections to the original XYZ file, not to previously corrected data.
