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Towards Quantifying Degree of Rock Weathering from Time Series Thermal Images

Megerssa, Leta Alemayehu (2010) Towards Quantifying Degree of Rock Weathering from Time Series Thermal Images.

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Abstract:Weathering degree is often estimated by methods requiring physical tests and expert judgments which are time consuming and depend on accessibility of the targets. In this study the radiant temperature variation of rock samples and rock masses with time over a day has been looked into for possible quantification of weathering degree. For this purpose temperature series images monitored over the duration of a day on artificial samples mosaic of Granite, Slate and Mudstone with varying degree of weathering and temperature images acquired from field sites of Slate rock mass slope and Granite rock mass slope were used. These are evaluated using indices obtained from the temperature series for the different weathering classes and compared with the weathering classes determined in the field following geotechnical guidelines. Lowest morning temperature record (A), maximum temperature record before direct solar irradiance (B), the temperatures after receiving 5, 30 and 80 minutes of direct solar irradiance (B, C, D) and the days peak temperature (F) of the rocks and their ratios were used as index . F/C and E/C ratio images gave relatively consistent increasing trend with weathering degree while B/A and D/C gave less consistent similar trend. Higher degree of overlap between the range of values for different lithologies were found suggesting possibility of transferable scale of measurement between different sites in the case of B/A and D/C ratios. The lack of overlap in F/C and E/C ratios suggests only a relative means of quantification for different sites requiring more reference information on the target to calibrate. In the rock mass outcrops temperature series image a method to represent the temperature inversion between morning and noon time images of weathered and un-weathered parts gave fairly consistent result to the expected. An attempt has been made to characterize the spectra features of the samples from the different degree of weathering. Apart from the elevated overall emissivity of the samples with weathering no significant change in spectral association could be found. Key words: Temperature series, degree of weathering, Quantitative, terrestrial IR.
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/92521
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