The distributed fibre optical temperature sensing technique represents a new physical approach for temperature measurements. Due to the time domain reflected measurement of the Raman backscattering effect of an optical fibre temperature measurements are possible with a high spatial and temperature resolution in one, two and three dimensions. It is shown that the fibre optic sensing technique gives quite new possibilities to detect and localize leakages in pipelines, wells and water constructions such as dams and dikes. In gas and oil pipelines leakages with very low leakage rates could be detected and localized. Leakage rates of even 50 ml/min at brine pipelines and of 10 ml/h at chemical pipelines could be detected. Measurements of the temperature distribution in underground gas storage facilities made simultaneously along the full length of a production string under varying operating conditions, especially before, during and after pressure drawdown of the annulus, provided detailed information on temperature anomalies which may be due to leakages from the production string or the casing or to flows occurring behind the casing. Further case histories show the efficiency and applicability of the sensing technique. Burning tests show that the fibre optic sensing technique has a good perspective for early fire detection and fire warning in cable routes in buildings and other constructions.
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