Remove Aircraft and Cosmic Effects

Use the RPS > Remove Aircraft and Cosmic Effects option (geogxnet.dll(Geosoft.GX.Radiometrics.RemoveAircraftAndCosmicEffects;Run)*) to remove aircraft and cosmic background contributions and produce background-corrected airborne radiometric data. For more details, refer to the Application Notes below.

Remove Aircraft and Cosmic Effects dialog options

Input channel suffix	Suffixes from channels generated by earlier processes (i.e., Along-Line Filtering, Account for Dead Time, or Generate Radioelement Counts) are automatically detected. By default, the suffix from the most recent process is preselected. Once a suffix is chosen, the associated channels are listed below the field. Script Parameter: SPECTRO.REMOVE_AIRCRAFT_AND_COSMIC_EFFECTS_INPUT_SUFFIX
Correction Coefficients - Aircraft and Cosmic Specify the aircraft background and cosmic stripping values - enter new values or accept the displayed defaults. See the Application Notes below for details.
Potassium (K)	Enter the Aircraft and Cosmic correction coefficients for the Potassium channel. Typical values: 12 and 0.032 Script Parameters: SPECTRO.KAIRBACK SPECTRO.KCOSSTRIP
Uranium (U)	Enter the Aircraft and Cosmic correction coefficients for the Uranium channel. Typical values: 2.2 and 0.026 Script Parameters: SPECTRO.UAIRBACK SPECTRO.UCOSSTRIP
Thorium (Th)	Enter the Aircraft and Cosmic correction coefficients for the Thorium channel. Typical values: 1.5 and 0.003 Script Parameters: SPECTRO.THAIRBACK SPECTRO.THCOSSTRIP
Total count (TC)	Enter the Aircraft and Cosmic correction coefficients for the Total count data. Typical values: 90 and 0.6 Script Parameters: SPECTRO.TCAIRBACK SPECTRO.TCCOSSTRIP
Upward Uranium (UpU)	Enter the Aircraft and Cosmic correction coefficients for the Upward Uranium data. Typical values: 0.6 and 0.008 Script Parameters: SPECTRO.UPAIRBACK SPECTRO.UPCOSSTRIP
Output channel suffix	Specify the suffix to append to output channels. Default: _bg. As you type, the information string below the field updates to reflect the new output channel names. Script Parameter: SPECTRO.REMOVE_AIRCRAFT_AND_COSMIC_EFFECTS_OUTPUT_SUFFIX

Application Notes

This tool applies corrections for cosmic and aircraft background radiation. It operates on pre-processed channels—labeled as *_filt if Along-Line Filtering has been applied to the current database and the default channel suffix has been retained—and generates background-corrected channels, which are labeled by default as *_bg.

Cosmic and Aircraft Background Corrections

Cosmic background radiation results from high-energy cosmic ray interactions with the atmosphere. The intensity of cosmic rays increases with altitude—approximately doubling every 2,000 meters—and exhibits minor variations with latitude.

In addition to cosmic radiation, background radiation is also generated by the aircraft (vehicle) and its onboard equipment. This is due to trace amounts of naturally occurring radioactive elements such as potassium (K), uranium (U), and thorium (Th) present in the materials used in the aircraft and its systems.

High-Altitude Cosmic Background Flights

The aircraft’s spectral contribution is assumed to be constant. The cosmic spectrum at each observation point is estimated by scaling a normalized cosmic spectrum by the cosmic window count rate. Each measured spectrum represents the sum of the aircraft component (constant) and the cosmic component. Both the aircraft and cosmic background components are then subtracted from the total gamma-ray counts.

Over open water, contributions from ground sources and atmospheric radon are minimal. To estimate the aircraft spectrum and the normalized cosmic spectrum, high-altitude flights are performed offshore, ideally in regions with low radon concentrations. Measurements are taken at multiple altitudes (e.g., 1.0, 1.5, 2.0, 2.5, and 3.0 km above sea level), with background count rates recorded across all energy channels. At each altitude, data is collected for a minimum of 2 minutes and up to 15 minutes, then averaged.

Aircraft and Cosmic Spectra

The measured spectra are each the sum of the aircraft component (constant) and the cosmic component. Since in the energy range of interest (0.7 to 3.072 MeV), the count rate in the cosmic window is linearly related to the count rate in the i’th energy channel, a linear regression of the cosmic window count rate on any other particular channel yields the cosmic sensitivity (slope of regression) and the vessel background (zero intercept) for that channel as follows:

• Slope (b): Cosmic sensitivity

• Intercept (a): Aircraft (vessel) background

For each of the 4 count windows, a least-squares (LSQ) linear fit is applied to determine the slope (b) and intercept (a) ^[1]:

The illustration below of aircraft and cosmic spectra is taken from the referenced IAEA International Atomic Energy Agency document ^[1] (p. 61).

Reviewing Results

Once processing is complete, review the raw, filtered, levelled, and corrected channels in the profile window to assess the impact of each correction step. If the results are unsatisfactory, adjust the parameter values and rerun the GX.

References