Africa Surveyors May-June issue 2023 digital

RADIOMETRICS SURVEY
mU and mK, for each of the three energy windows; and their values
are dependent on the size of the crystals and detector altitude.
During a low altitude survey, the presence of atmospheric radon and
cosmic rays can also affect the count rates in each of the three spectral
bands. The effect of these non-geologic sources on the count rates
is primarily due to Compton scattering and the fact that they have a
lower energy than gamma rays originating from the earth's surface.
To reduce the impact of background noise on the spectral windows
and count rates, a special spectrometer called a "differential
spectrometer" is used. The difference between this spectrometer and
the multichannel spectrometer is that it does not use "windows" of
fixed energy width; instead, a narrower range of energy windows
are measured. The detectors are of a larger size, and the light
flash counting rates are much lower than with the multichannel
spectrometer.
The optimum line spacing depends on the survey type and the amount
of detail that is required. For fixed wing surveys, a mean terrain
clearance of 130 metres is recommended, and the line spacing should
be about three times this.
For unmanned aerial geophysical systems (UAS) this spacing is not
as critical, and the distance between the surveyed strip and the
closest point on the ground should not exceed half its diameter. For
this reason a circle of investigation is often used for the strip, which
moves with the aircraft. The main value of low altitude radiometrics
is the ability to map uranium dispersion halos, and to indicate local
anomalies in the U/Th and U/K ratios as "red-balls" or "black balls".
In suitable areas these maps can be useful as aids in geological
interpretation.
“High resolution magnetic and spectrometric surveys on an
airborne platform are routinely being carried out over huge areas in
understanding the subsurface structure and mineral potential and
in narrowing down the areas of interest for subsequent follow-up.
Airborne spectrometric surveys are also being conducted to track the
radioactive plumes in the event of nuclear disasters in atomic power
plants for safety from environmental perspective,” says Ramesh.
Important aspect of Radiometrics survey
The important aspect of radiometric surveys is that they can detect
subtle variations in the natural background radiation. These changes
are generally not detectable from the ground, but can be detected by
using "upward looking" crystals that are shielded from atmospheric
radiation and can therefore monitor these variations in real time
during the survey.
“One important aspect of radiometric surveys is their ability to
provide reliable, consistent, and calibrated data. Variations in lighting
conditions or camera settings can be accounted for and do not
compromise the quality and comparability of the imagery captured
over time,” affirms Susanne Scholz, Application Engineer at Vexcel
Imaging. “Precise calibration of the imaging system is a fundamental
prerequisite to achieving such a high level of reliability. In our
calibration lab, our UltraCam aerial camera systems undergo both
geometric and radiometric calibration processes, transforming them
into precise measurement instruments,” she adds.
Changes in the natural background can lead to errors in the
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