Satellite survey of gas flares:development and application of a Landsat-based technique in the Niger Delta

摘要

Pollution from oil and gas exploitation in the Niger Delta has greatly endangered the natural ecosystem, with gas flaring identified as a key agent of environmental pollution in the region. Efforts to evaluate the impacts of flaring on the surrounding environment have been hampered by limited access to official information on flare locations and volumes; hence an alternative method of acquiring such information is needed. This paper describes the development and application of the Landsat Flare Detection Method (LFDM), based on the combination of the near, shortwave and thermal infrared bands of Landsat imagery. The technique was validated using a reference dataset of flare locations interpreted from aerial photographs, achieving a user accuracy of 86.67%. The LFDM was applied to a time-series of imagery (1984 to 2012 inclusive) to obtain a long term flaring history of the region; 303 flares (251 onshore and 52 offshore) were detected over the study period. The spatiotemporal distribution of these flares corresponds with known variations in oil and gas activities in the region. There was considerable variation between states in the trajectories of gas flaring activity and the proportion of onshore versus offshore flaring, which indicates substantial spatiotemporal variations in the environmental impacts of this industry. The LFDM builds upon existing methods of flare detection, which were based on moderate resolution imagery, by offering: increased precision of flare location estimates, improved objectivity, accurate identification of onshore and offshore flares and a long flaring history. The LFDM is an efficient and cost effective method which is able to provide local to regional scale information which is complementary to that derived from other remote methods of flare detection and ground-based surveys. It could thus be used for either backward (flare history) and/or forward (monitoring) surveys, especially in monitoring the country’s progress towards the recently set 30% flare reduction target by 2017.