The gamma-ray data for digital soil mapping in Thailand

The gammaA geo-referenced airborne gamma-ray image of the study area at nominal scale 1:250,000, produced for the Thai Department of Mineral Resources (Kenting Earth Science International limited (KESIL), 1982; Wisedsind et al., 1994) was acquired. The AGRI data was collected at the beginning of the winter season in November 1985 by aircraft with flight line spacing of 2 km, terrain clearance of 400 m and a flight line direction west to east, flown at a constant height above the ground of 400 ft (MTC). The production of radiation and ternary radiation maps of Thailand were produced using IAEA method (Angsuwathana and Chotikanatis, 1997; IAEA, 2003), which resulted in an image with 400 x 400 m pixels. The gamma-ray spectrometer, developed by KESIL, contained 12 crystals in a 50.34 litre Harshaw NaI (Tl) crystal scintillator and recorded gamma-rays in 256 channels. The measured energy spectrum ranges from 0 to 3 MeV (wavelengths between 0.03 x 10-4 to 4.13 x 10-4 nanometres). The sensor measures the natural radiation from decay series of potassium (K), thorium (Th) and uranium (U) in the upper 45 cm of the Earth’s surface. The following energy windows were used to measure the total count (TC) and three radioelements: TC = 0.40-2.82 Mev., K = 1.36-1.56 Mev., U = 1.66-1.86 Mev., and Th = 2.42-2.82Mev. Potassium is measured directly from the decay of 40K and is expressed as a percentage. Thorium and Uranium are inferred from daughter elements associated with distinctive isotopic emissions from 208Tl and 214Bi in their respective decay chains and are expressed in equivalent parts per million and coded as eU and eTh. A complication is that 214Bi is also a decay product of radon gas, 222Rn, itself a decay product of radium, 226Ra. Radon concentration is highly dependent on soil moisture, being practically absent near the surface in dry soil and abundant in saturated soil (Grasty, 1997). Another complication is that the signals for 40K and 208Tl (i.e., eU) are attenuated in wet soil; this has been used to map soil moisture in homogeneous soil materials using K/eTh ratios (Carroll 1981). Atmospheric Rd is also affected by changes in air density due to temperature and pressure, thus data acquired in cool high-pressure conditions may have up to 30% enhanced Rd compared to warm low-pressure, thereby distorting the eU signal (IAEA, 2003). For these reasons the eU signal is considered less reliable than those for K and eTh.-ray imager

Fuzzy logic for fine-scale soil mapping: A case study in Thailand

Conventional soil survey methods are labor intensive and prohibitively expensive considering the area to be covered. Unfortunately, the current soil survey products are not adequate, either categorically or cartographically, and cannot be easily downscaled for its application at farm-level. On the other hand soil is a continuous variable and does not have abrupt boundaries in nature. One soil type can change gradually to become another class. This creates problem in delineating soil boundaries due to overlapping of classes. In this situation fuzzy logic can be useful. In conventional soil survey, this is solved by creating mapping units such as consociation, association or complex. In consociation the delineated areas are dominated by one soil type (at least 75%) with some inclusion of other soils. When dissimilar soils occur in a consistent repeating pattern, it is mapped as an association. In classification using fuzzy logic a pixel may have multiple class membership and the one with the highest membership or similarity value gets the class label. The main objective of the study is to assess the usefulness of fuzzy logic in increasing efficiency in soil mapping. The study was conducted in Lomsak, Phetchabun province in Thailand. An expert system was used whereby rule-based reasoning was applied for mapping soil series and topsoil texture in which the soil-landscape relationship was taken into account. Lithology and terrain parameters were used as predictor variables. This resulted in mapping 17 soil series and 10 topsoil texture classes in a complex landscape. In the conventional soil survey technique, it is possible to map only 8 soil series at 1:50,000 scale, indicating that detail soil mapping is possible by using fuzzy logic. The accuracy of the fuzzy logic derived soil series map was tested using a set of evaluation data. The result showed an average accuracy of 70%. Fuzzy logic has the potential for reducing inconsistency and costs associated with the traditional soil mapping processes as mapping can be carried out with a relatively low density of soil samples. The research results can be used to support soil survey works in complex landscapes at sub-watershed scale

The gamma-ray data for digital soil mapping in Thailand

The gammaA geo-referenced airborne gamma-ray image of the study area at nominal scale 1:250,000, produced for the Thai Department of Mineral Resources (Kenting Earth Science International limited (KESIL), 1982; Wisedsind et al., 1994) was acquired. The AGRI data was collected at the beginning of the winter season in November 1985 by aircraft with flight line spacing of 2 km, terrain clearance of 400 m and a flight line direction west to east, flown at a constant height above the ground of 400 ft (MTC). The production of radiation and ternary radiation maps of Thailand were produced using IAEA method (Angsuwathana and Chotikanatis, 1997; IAEA, 2003), which resulted in an image with 400 x 400 m pixels. The gamma-ray spectrometer, developed by KESIL, contained 12 crystals in a 50.34 litre Harshaw NaI (Tl) crystal scintillator and recorded gamma-rays in 256 channels. The measured energy spectrum ranges from 0 to 3 MeV (wavelengths between 0.03 x 10-4 to 4.13 x 10-4 nanometres). The sensor measures the natural radiation from decay series of potassium (K), thorium (Th) and uranium (U) in the upper 45 cm of the Earth’s surface. The following energy windows were used to measure the total count (TC) and three radioelements: TC = 0.40-2.82 Mev., K = 1.36-1.56 Mev., U = 1.66-1.86 Mev., and Th = 2.42-2.82Mev. Potassium is measured directly from the decay of 40K and is expressed as a percentage. Thorium and Uranium are inferred from daughter elements associated with distinctive isotopic emissions from 208Tl and 214Bi in their respective decay chains and are expressed in equivalent parts per million and coded as eU and eTh. A complication is that 214Bi is also a decay product of radon gas, 222Rn, itself a decay product of radium, 226Ra. Radon concentration is highly dependent on soil moisture, being practically absent near the surface in dry soil and abundant in saturated soil (Grasty, 1997). Another complication is that the signals for 40K and 208Tl (i.e., eU) are attenuated in wet soil; this has been used to map soil moisture in homogeneous soil materials using K/eTh ratios (Carroll 1981). Atmospheric Rd is also affected by changes in air density due to temperature and pressure, thus data acquired in cool high-pressure conditions may have up to 30% enhanced Rd compared to warm low-pressure, thereby distorting the eU signal (IAEA, 2003). For these reasons the eU signal is considered less reliable than those for K and eTh.-ray imager