Hyperspectral reflectance of vegetation affected by underground hydrocarbon gas seepage

Anomalous concentrations of natural gas in the soil may be sourced from leaking underground gas pipelines or from natural microseepages. Due to the explosive nature of hydrocarbon gases, early detection of these gases is essential to avoid dangerous situations. It is known that natural gas in the soil affects vegetation health, which may be detected through analysis of reflectance spectra. This thesis characterizes the effects of underground gas leakage on plant and canopy development and reflectance. Based on the reflectance properties, a general gas leak detection method is proposed.It was assumed that natural gas displaces the soil air and that oxygen shortage is the cause of changes in vegetation growth and reflectance; however it was not known whether the hydrocarbon gases have an additional effect on the vegetation. Therefore two experiments were performed to compare the effects of small gas leaks (without oxygen shortage) with large leaks (with oxygen shortage) on plant growth and reflectance. The small gas leaks were simulated by delivering natural gas, methane and ethane to pots with maize (Zea mays) and wheat (Triticum aestivum) plants. The large natural gas leak was simulated by delivering 2200 1 of gas per day to 2 by 2 m maize and wheat canopy plots. Whereas in several studies a decrease in vegetation chlorophyll was one of the main indicators of large gas leaks, this study showed that leaf area is a better indicator of gas leakage. Moreover, it was shown that when the ethane concentration in the soil reaches 0.75%, plant growth is not only affected by oxygen shortage but also by the gas itself.The leaf reflectance of the plants was analysed using continuum removal of the blue (400-550 nm), red (550-750 nm) and two water absorption features (1370-1570 nm and 1870-2170 nm). The analysis showed that ethane caused an initial increase of 10% in reflectance between 560 and 590 nm, followed by a decrease during the course of the experiment. All gases caused a