Regularity Analysis of Airborne Natural Gamma Ray Data Measured in the Hoggar Area (Algeria) - Advances in Data, Methods, Models and Their Applications in Geoscience - page 95

3. Overview on the analyzed GR measurements
The analyzed GR measurements are recorded during a magneto-spectrometric survey
accomplished, between 1971 and 1974 over the Hoggar, for the purpose of the mining
research and the regional geological mapping.
The technical characteristics of the survey are:
 Two types of planes :
 Douglas DC-3.
 Aero Commander.
 Navigation System: Doppler type A DRA-12
 Magnetic Compass of type Sperry CL 2, with a resolution of 1°.
 Radar altimeter with an accuracy of 30 feet (type Honeywell Minneapolis).
 Camera with a continuous 35 mm-film
 Acquisition system of data (type Lancer) for the recording of the numerical data on
magnetic tapes of 1/2".
 Two types of graphic recorders: with 2 and 6 channels for the graphic monitoring of the
magnetic and spectrometric profiles respectively.
 Two types of magnetometers:
 Magnetometer with optical pumping with the Cesium (model VARIAN) of
resolution of 0.02 NT (nano Tesla).
 Magnetometer Flow-gate of a resolution of 0.5 NT.
 NaI(Tl) spectrometer with four (04) channels: Total Count (TC), Uranium (U), Thorium
(Th) and Potassium (K).
The parameters of airborne spectrometric survey carried out over the Hoggar area are:
 The average of the flight height is fixed at 500 feet (approximately 150 m).

 The direction of the profiles: perpendicular to the geological structures.

 The distance between lines varies from 2 to 5 kilometers according to the areas, but on

average it is about two kilometers.

 The distance between the observation points is approximately 46.2 m (152 feet).

4. Corrections of the airborne natural activity measurements

The measurements acquired during an airborne spectrometric survey can not be exploited
in a raw state, but need to be corrected mainly from aircraft background, stripping (or
Compton) effect and height effect (IAEA, 2003).
Background corrections
There are three components of the background correction:
 The instrument background (called ''aircraft background'' in airborne gamma
spectrometry),
 The cosmic background arisen from the reaction of primary cosmic radiation with
atoms and molecules in the upper atmosphere.
 The effect of atmospheric radon. In portable or car-borne gamma ray surveys, the
background component is usually small relative to the signal from the ground.
The observed count rates in the four channels: Total Count (TC), Potassium (K), Uranium
(U) and Thorium (Th), are corrected for the background effects using the following
formulae: