Heading Correction

Use the Database Tools > Corrections > Heading Correction menu option (HEADING GX) to apply a heading correction to data for a systematic shift (in the data) that is a function of the direction of travel for a survey line.

The option is also available with the following extensions and menus:

Geophysics Levelling: Tie Line Levelling > Levelling Corrections
UAV Merge Sorties: UAV Merge Sorties > Pre-processing

Heading Correction dialog options

Heading table name

Specify the name of the heading table file. The heading file format is described in the Application Notes below.

Script Parameter: HEADING.TABLE

Channel to correct

Select the name of the channel to correct.

Script Parameter: HEADING.IN

Output corrected channel

Select the output corrected channel name, which may be the same as the input channel.

Script Parameter: HEADING.OUT

Application Notes

The magnetic field response varies with declination. Flight paths rarely follow an ideal linear course; as a result, the variation in the direction affects the intensity of the magnetic response. The heading correction intends to eliminate the variability due to changes in survey direction, and adjust the data as if it was all flown in the same direction.

In modern surveys, heading corrections are normally included as part of the aircraft compensation corrections, which are performed automatically by the survey data acquisition system. Older surveys, or improperly compensated surveys, may still require a heading correction as part of data processing. Refer to the survey specifications to determine if you should apply the heading correction.

Heading corrections can be determined by flying in different directions, often in the form of a clover leaf, over the same point at a high altitude or over water. The purpose of flying at a high altitude or over water is to reduce the potential effect of geophysical responses from the geology and measure the earth field response in different directions. At the minimum, the heading is determined by flying in the four cardinal compass directions (North, South, East and West), or in the two opposite directions parallel and perpendicular to the planed survey lines. The difference between the average at the intersection and the measured values in each direction then constitutes the heading correction.

The heading corrections must be compiled into a small Geosoft heading table <link to Geosoft Table File> in the following format:

/  Geosoft Heading Correction Table

/= Direction:real:i

/= Correction:real

/ Direction Correction

0 -3.25

90 -0.42

180 +3.19

270 +0.48

360 -3.25

The directions are with respect to the Y axis of the survey coordinate system, and a heading correction in the 0 and 360 degree directions must be specified. If the heading test is flown in the directions of the planned survey lines, you must calculate a 0 and 360 degree correction for the table by interpolating between the observed corrections.

Example of a heading test flown for survey lines 30 degrees East of the Y axis:

/  Geosoft Heading Correction Table

/= Direction:real:i

/= Correction:real

/  Direction Correction

0 -5.05

30 -10.88

120 -4.87

210 +9.13

300 +6.63

360 -5.05

The directions listed in the table must be in the true heading. The correction in directions between those specified is linearly interpolated.