Plant spectral responses to gas leaks and other stresses

The study aimed to assess the ability of remote sensing to differentiate between plant stress caused by natural gas leakage and other stresses. In order to use satellite remote sensing to detect gas leaks it is necessary to determine whether the cause of the stress can be identified in the spectral response and distinguished from other stress factors. Field plots of oilseed rape (Brassica napus) were stressed using elevated levels of natural gas in the soil, dilute herbicide solution and extreme shade. Visible stress response, spectral stress response and chlorophyll content of plants from these three treatments were compared to control plants receiving no treatment. The reflectance from isolated leaves was measured in the laboratory. Spectral responses to stress included increased reflectance in the visible wavelengths and decreased reflectance in the near-infrared. A shift of the red edge position towards shorter wavelengths was observed as a result of all three stresses, although the shift was greatest when stressed via extreme shade. Red edge position was strongly correlated with chlorophyll content across all the treatments. The ratio of reflectances centred on the wavelengths 670 and 560 nm was used to detect increases in red pigmentation in gassed and herbicide-stressed leaves. Stress due to extreme shade could be distinguished from stress caused by natural gas or herbicide by changes in the reflectance spectra, however, stress caused by herbicide or natural gas could not be distinguished from one another in the spectra although symptoms of stress caused by elevated gas levels were identified earlier than symptoms caused by herbicide-induced stress.