# On the Potential of the RST-FLARE Algorithm for Gas Flaring Characterization from Space
## 1 Introduction
Most of the satellite techniques proposed and currently applied for detecting gas flaring platforms as well as to assess their spatiotemporal variations [7; 12; 16; 17; 21; 22; 23; 24; 25] are based on measurements acquired by different sensors (e.g., Operational Linescan System--OLS, Moderate Resolution Imaging Spectroradiometer--MODIS, Visible Infrared Imaging Radiometer Suite--VIIRS, Along-Track Scanning Radiometer--ATSR, Land Remote-Sensing Satellite--Landsat) in different portions of the electromagnetic spectrum (visible--VIS, near-infrared--NIR, shortwave infrared--SWIR, middle Infrared--MIR, thermal infrared--TIR). Considering that gas flares typically operate at temperatures \(>\)1450 K with a mean of around 1750 K [7; 20; 21], their peak spectral radiant output occurs in the SWIR spectral region, centered around 1.6 \(\upmu\)m [7; 25; 26]. The latter is then the most suitable spectral region to be used for investigating these phenomena. On the other hand, when sensors not able to acquire information in this region are used, like MODIS in nighttime conditions, the MIR bands (centered around 3.5 \(\upmu\)m) are the most used [7]. This portion of the electromagnetic spectrum falls on the trailing edge of gas flare radiant emissions, therefore observes a mixture of flare plus background (always contributing to the signal) radiant emissions [7]. Flare radiant emissions at these wavelengths are indeed about one third of the emissions at 1.6 \(\upmu\)m, as suggested by [7] and [26], hence, for high temperature gas flares, a significant proportion of flaring activity is not observable above the MIR background [7]. Once selected the most suitable channel(s), gas flares can be separated from other IR emitters based on temperature and temporal persistence (i.e., a presence at the same location on multiple observations over a set period) [7; 23; 24; 25]. With reference to the estimation of gas flared volumes, a regression model is usually applied [7; 16], requiring, for its calibration, a diagnostic parameter aimed at quantifying the emission power of the source (e.g., the sum-of-lights index for OLS data--[16], the Fire Radiative Power for MODIS--[20] and VIIRS [26] data or the monthly sum of cloud and sampling normalized radiant heat estimates for VIIRS data--[7]) and official data on volumes of gas flared. It is worth noting that actual improvements in this field would be achieved by using multiple satellite data sources and when reliable sources of in situ measurements of gas flaring volumes for calibration would be available. Among the few existing algorithms, ad hoc developed for gas flaring analysis, a new methodology has been recently proposed by [20] for computing the volumes of gas annually flared by a specific plant (i.e., Centro Olo Val d'Agrit--COVA), located in southern Italy, through the analysis of time series of night-time MODIS data acquired in the infrared region. Such a methodology provided accurate estimates (R\({}^{2}\) -83%) of the volumes of gas emitted by COVA on an annual basis, with an error of about 2%. Starting from these encouraging outcomes, in this paper, the field of applicability of such a method has been extended further, adding a preliminary step aimed at the detection of areas affected by gas flaring activity. By this way, a more general approach is here proposed, named RST-FLARE. Such a method is described in this paper and its performances, achieved while analysing the Niger Delta region, are shown and discussed. Respect to the previous application (i.e., COVA) the use case here presented is significantly different as: (i) the amount of gas flared is dramatically higher; (ii) the number of flaring sites is enormously larger; (iii) the flaring site locations are not \"a priori\" known. The accuracy of the achieved results will be evaluated for comparison with other satellite products; with respect to the gas flared volumes, the information arising from official datasets independently provided by international/national organizations will be also considered.