process of reducing organic matter and deteriorating soil physical properties –
especially infiltration rates, boosting overland flows and soil losses.
2.2 Gamma-Ray Spectrometry: A Useful Tool for Soil Mapping
in Inaccessible Terrain and Data-Scarce Regions
2
The northern Thai highlands can be considered a neglected area due to its low
level of accessibility, its terrain and the minority ethnicities living there. This
neglected situation is also true with respect to the baseline data available for
planning purposes, such as soil information. In Sect. 2.3, advances with respect
to the collection of soil information using new mapping approaches, including
the use of indigenous knowledge and geo-statistics, will be outlined; however,
these approaches are laborious if the gathering of consistent regional information
is the objective. For three reasons, gamma-ray spectrometry can be considered a
potentially suitable data source if one wishes to build regional soil information
for the highland areas of northern Thailand. First, nationwide gamma-ray data
are available via the Department of Mineral Resources (DMR), plus the gammaray spectra for this area show a higher variability than the official soil maps
(Vijarnsorn and Eswaran 2002), in which about 80 % of the surface is
represented as one undifferentiated map unit called ‘slope complex’. The third
reason is that Tulyatid and Rangubpit (2004) published a conference paper on
regolith mapping in southern Thailand, showing that weathering influences the
gamma-ray signal, and that because chemical weathering is one of the dominant
soil forming processes, the gamma-ray signal must therefore incorporate soil
information. This hypothesis is based on the fact that 90 % of gamma-rays
emanate from the top 30–45 cm of the earth’s surface (Gregory and Horwood
1961), which is dominated – including in the steep terrain found in areas of
northern Thailand – by soil and not by parent rock. Consequently, if the parent
rock is sufficiently transformed – especially in the geochemical sense – the soil
signal should differ from the parent rock signal and might even be stronger. In
order to test this hypothesis, in the studies here, ground-based gamma-ray
measurements were correlated with on-site soil information, as well as with
aerial gamma-ray spectra. In the following, we first present gamma-ray spectrometry as a method, then elaborate more upon why this method is helpful for
soil mapping, before presenting the results of studies carried out on different
spatial scales in the northern Thai highlands, and the conclusions reached
therein.
2 This section was written by Ludger Herrmann, Ulrich Schuler, Petra Erbe, Wanida Rangubpit,
Adichat Surinkum and Karl Stahr.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
35
especially infiltration rates, boosting overland flows and soil losses.
2.2 Gamma-Ray Spectrometry: A Useful Tool for Soil Mapping
in Inaccessible Terrain and Data-Scarce Regions
2
The northern Thai highlands can be considered a neglected area due to its low
level of accessibility, its terrain and the minority ethnicities living there. This
neglected situation is also true with respect to the baseline data available for
planning purposes, such as soil information. In Sect. 2.3, advances with respect
to the collection of soil information using new mapping approaches, including
the use of indigenous knowledge and geo-statistics, will be outlined; however,
these approaches are laborious if the gathering of consistent regional information
is the objective. For three reasons, gamma-ray spectrometry can be considered a
potentially suitable data source if one wishes to build regional soil information
for the highland areas of northern Thailand. First, nationwide gamma-ray data
are available via the Department of Mineral Resources (DMR), plus the gammaray spectra for this area show a higher variability than the official soil maps
(Vijarnsorn and Eswaran 2002), in which about 80 % of the surface is
represented as one undifferentiated map unit called ‘slope complex’. The third
reason is that Tulyatid and Rangubpit (2004) published a conference paper on
regolith mapping in southern Thailand, showing that weathering influences the
gamma-ray signal, and that because chemical weathering is one of the dominant
soil forming processes, the gamma-ray signal must therefore incorporate soil
information. This hypothesis is based on the fact that 90 % of gamma-rays
emanate from the top 30–45 cm of the earth’s surface (Gregory and Horwood
1961), which is dominated – including in the steep terrain found in areas of
northern Thailand – by soil and not by parent rock. Consequently, if the parent
rock is sufficiently transformed – especially in the geochemical sense – the soil
signal should differ from the parent rock signal and might even be stronger. In
order to test this hypothesis, in the studies here, ground-based gamma-ray
measurements were correlated with on-site soil information, as well as with
aerial gamma-ray spectra. In the following, we first present gamma-ray spectrometry as a method, then elaborate more upon why this method is helpful for
soil mapping, before presenting the results of studies carried out on different
spatial scales in the northern Thai highlands, and the conclusions reached
therein.
2 This section was written by Ludger Herrmann, Ulrich Schuler, Petra Erbe, Wanida Rangubpit,
Adichat Surinkum and Karl Stahr.
2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . .
35