# On the Potential of the RST-FLARE Algorithm for Gas Flaring Characterization from Space
## 1 Introduction  
Gas flaring is one of the processes, together with venting and reinjection, widely used to dispose of natural gas produced at oil and gas facilities, especially in situations where there is insufficient infrastructure to use the gas locally or move it to market [1]. It represents a foremost anthropogenic source for greenhouse and/or precursor gases, particulate matter and black carbon [2, 3] that pollute the air, soil and water, with huge impacts on humans, the environment and the economy [3, 4, 5, 6, 7]. The World Bank estimates that over 150 billion cubic meters (BCM) of natural gas is flared annually, an amount worth approximately 30.6 billion dollars, equivalent to 5% of the world's natural-gas consumption [8] and causing 400 million tons of carbon dioxide (CO\({}_{2}\)) discharged into the atmosphere [9]. Nevertheless, oil companies continue to annually flare billions of cubic meters of natural gas. New data recently released by Global Gas Flaring Reduction Partnership (GGFR) for 2016 revealed an increase of 2 BCM, from the previous year (i.e., 147 BCM), in the amount of gas flared at oil production sites worldwide, reversing a general trend of gas flaring reduction, observed in the previous two years [10]. Such an increase is mainly attributed to an overall growth in oil production, particularly in Russia, Iran and Iraq [10]. In the rest of the world, especially in the United States and Nigeria, gas flaring has significantly declined in the past two years while oil production levels have remained unchanged [10, 11]. The main challenges involved in addressing environmental aspects of flaring consist in recognizing the most affected areas worldwide and determining how much emission is actually released. Until recently, several factors have hampered an empirical assessing of the environmental impacts of flaring: (i) a limited access to official information on flaring locations; (ii) the heterogeneity in spatial and temporal sampling strategies; (iii) the methods used to collect data and (iv) the lack of auditability [7; 12]. Furthermore, even when data on gas flared volumes are available, they typically are: (i) self-reported by the flare operators and (ii) roughly estimated on the basis of the difference between the natural gas volume produced and the quantity used or sold. The difficulty in assessing the reliability and accuracy of the reported data [12] points out the need of developing robust, consistent and objective methodologies of data analysis able to provide independent information about active flaring sites localization, the amount of gas flared volumes at both site and country scale and flare volumes changes over space and time [12]. A valid way to bridge this gap and to have independent information on gas flaring activity at global, national and regional scale might come from the use of Earth Observation (EO) satellites, owing to their continuous and repetitive observations, multispectral capabilities and synoptic coverage [12; 13]. In particular, the implementation of methodologies based on the use of long-term time series of satellite data has demonstrated its potential and usefulness for this aim. In detail, satellite-based methods allow to map and monitor the distribution of flaring sites over a large area, both in night-time [12; 14; 15; 16] and daytime conditions [17; 18], and to characterize such a phenomenon in terms of emitted gas volumes [12; 16; 19; 20], consumption of CH\({}_{4}\) and release of CO\({}_{2}\)[21].