University of Twente Student Theses

Spatial prediction of topsoil properties through the application of gamma ray spectrometry in Quarternary sandy material in Nong Sung District, Thailand for environmental studies

Fakeye, Attah Motunrayo (2009) Spatial prediction of topsoil properties through the application of gamma ray spectrometry in Quarternary sandy material in Nong Sung District, Thailand for environmental studies.

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Abstract:	The use of soil sensors to map fine–scale soil information for environmental studies is becoming prominent as there is an increasing demand for effective and efficient method of mapping soil properties. Gamma ray spectrometry is one of the techniques gaining weight over the conventional soil sampling method because of its goal in minimising huge soil survey cost whilst maximizing economic returns. Relatively, as a new soil sensing technique, it can potentially map soil variations by improving the mapping of soil texture, available potassium (avK). Gamma – soil mapping is largely the application of sensing technology and soil information to in-field data gathering. In this research, we look at the possibility of calibrating gamma ray concentrations to predict various surface soil properties like soil texture (clay, sand and silt fractions), available potassium (avK), pH and electrical conductivity (EC). The concentrations of 40K, 238U and 232Th in sandstone washed materials were measured in situ by portable Exploranium GR 320 gamma ray spectrometer. Simultaneously, soil samples were collected from the fields and analysed in the laboratory. Three plots (Nong Suang, Ban Nong Ta Net and Bang Moi Kwok) in Nong Sung District, Nakhon Ratchasima Province, NE Thailand were surveyed. The results of spatial distribution of radioelements in the topsoil layer were presented. On-ground γ-rays concentrations derived from 40K (otherwise denoted by γK) was rather homogenous in a limited content across the study area. This is as expectations based on the geo-lithological nature of soil which consists predominantly of washed deposits of sandstone eroded in the Quarternary age. The lowest concentration (34.3 ± 0.6 Bq/kg) occurred in plot 1, and highest (38.1 ± 0.7 Bq/kg) in plot 3, indicating a uniform distribution. The recorded γK values and total gamma ray intensities were related to the soil texture and avK properties obtained in the laboratory. Statistically significant correlation was identified with avK, clay and sand properties. Strong linear relationships identified range between γK and avK (r2 = 0.78, P < 0.001); and also with surface texture (r2 = 0.48 to 0.67). The success of γ-ray spectrometry in predicting avK and other properties relied on this strong relationship held in all plots which was to transform γK map into a 0.2 m resolution soil property map by regression analysis. This regression was associated with up to 78% of the variance in avK and % clay 51%. The overall lowest RMSE were 0.8 % clay and 1.3 mg/kg avK contents.
Item Type:	Essay (Master)
Faculty:	ITC: Faculty of Geo-information Science and Earth Observation
Programme:	Geoinformation Science and Earth Observation MSc (75014)
Link to this item:	https://purl.utwente.nl/essays/91634
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