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 93

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Regularity Analysis of Airborne Natural
Gamma Ray Data Measured in
the Hoggar Area (Algeria)
Saïd Gaci 1 , Naïma Zaourar 1 , Louis Briqueu 2
and Mohamed Hamoudi 1
1 University of Sciences and Technology Houari Boumediene, Algiers,
2 Laboratoire Géosciences- University Montpellier 2- CNRS, Montpellier,
1 Algeria
2 France
1. Introduction
The airborne Gamma Ray (GR) measurements have been used since decades in geophysical
research. The airborne measurement of gamma radiation emitted by naturally occurring
elements finds applications in: geological mapping (Graham and Bonham-Carter, 1993;
Jaques et al. , 1997; Doll et al. , 2000, Aydin et al., 2006; Sulekha Rao et al. , 2009), regolith and
soil mapping (Cook et al. , 1996; Wilford et al. , 1997; Bierwirth and Welsh, 2000), mineral
exploration (Brown et al. , 2000), and hydrocarbon research (Matolín and Stráník, 2006).
Potassium (K), Uranium (U) and Thorium (Th) are the three most abundant, naturally
occurring radioactive elements. The K element is the main component of mineral deposits,
while Uranium and Thorium are present in trace amounts, as mobile and immobile
elements, respectively. The concentration of these different radioelements varies between
different rock types, thus the information provided by a gamma-ray spectrometer can be
exploited for needs of the rocks cartography. The obtained maps allow to localize
radioelement anomalies corresponding to zones disrupted by a mineralizing system.
The approach presented in this chapter deepens the results derived from the conventional
study. It consists on a mono(two)-dimensional fractal analysis of natural radioactivity
measurements recorded over the Hoggar area (Algeria).
The natural radioactivity measurements, like other geophysical signals, contain a
deterministic and a stochastic components. The former part holds information related to the
regional aspect, while the latter reflects the local heterogeneities. As the raw spectrometric
data need to be processed before any exploitation, the stochastic component can be altered
and some information about heterogeneities is lost.
Here, we show first the fractal behavior of the analyzed GR measurements. In addition, it is
demonstrated that this behavior is not affected by all the pre-processing operations
(spectrometric corrections and 2D-interpolations). The corrections are not then necessary.
Since the analyzed data exhibit a fractal exponent varying with the spatial position, they are
modeled as paths of multifractional Brownian motions (mBms) (Peltier and Lévy-Véhel,
1995).