Peat Mapping Associations of Airborne Radiometric Survey Data

Abstract

This study considers recent airborne radiometric (gamma ray) survey data, obtained at high-resolution, across various regions of the UK. The datasets all display a very evident attenuation of signal in association with peat, and intra-peat variations are observed. The geophysical response variations are examined in detail using example data sets across lowland areas (raised bogs, meres, fens and afforested peat) and upland areas of blanket bog, together with associated wetland zones. The radiometric data do not map soils per se. The bedrock (the radiogenic parent) provides a specific amplitude level. Attenuation of this signal level is then controlled by moisture content in conjunction with the density and porosity of the soil cover. Both soil and bedrock variations need to be jointly assessed. The attenuation theory, reviewed here, predicts that the behaviour of wet peat is distinct from most other soil types. Theory also predicts that the attenuation levels observed across wet peatlands cannot be generally used to map variations in peat thickness. Four survey areas at various scales, across England, Scotland, Wales and Ireland are used to demonstrate the ability of the airborne data to map peat zones. A 1:50 k national mapping of deep peat is used to provide control although variability in the definition of peat zones across existing databases is also demonstrated.

Assessing Soil Wetness with Airborne Radiometric Data

“…The threshold of 800 cps is used since it largely outlines the extent of the Blanket Bog as defined in Figure 2a. As is usual in radiometric peat studies (Beamish, 2014), intra-peat variations are observed and the lowest interval (e.g. < 100 cps) would imply 100% saturation.…”

“…Peat soils, in particular, produce readily identifiable attenuation zones. The radiometric data can therefore be used for peat mapping and hence assessments of the lateral extent of the carbon store (Beamish, 2014). Although the bedrock provides a specific radiogenic level with associated radiochemical attributes, attenuation of the signal level is controlled by soil moisture content in conjunction with the density and porosity of the soil cover.…”

Environmental radioactivity in the UK: the airborne geophysical view of dose rate estimates

“…Each survey provides a spatially-dense radioelement mapping with derived dose rates. An example is first provided using data from the latest (2013) TellusSW survey Beamish et al, 2014). Figure 3a shows a radioelement ternary image formed from the three %K, eTh and eU contributions.…”

“…In the limiting case of wet peat attenuation levels increase by >50% over their 'dry' equivalents. The behaviour is so distinctive that dose-rate estimates can be used to map peat areas across the UK (Beamish, 2014).…”

“…Peat soils, in particular, produce readily identifiable attenuation effects. The radiometric data can therefore be used for peat mapping and hence assessments of the lateral extent of the associated carbon store (Beamish, 2014). Although the bedrock provides a specific radiogenic level with associated radiochemical attributes, attenuation of the signal level is controlled by soil moisture content in conjunction with the density and porosity of the soil cover.…”