# On the Potential of the RST-FLARE Algorithm for Gas Flaring Characterization from Space
## 4 Validation Analyses
### Gas Flared Volumes  
The volumes of gas annually flared in Niger Delta were computed by the two RST-FLARE models developed using OPEC and EIA data (Table 2). These estimates, shown in Figure 12 (blue line for the OPEC-based model and pink line for the EIA one), were first compared with volumes provided by MOVET in the period 2000-2014 (black dotted line in Figure 12) and VNF in years 2012-2016 (green line in Figure 12). The NNPC data (solid grey line in Figure 12) are then used to validate the RST-FLARE products, offering the longest temporal series. Concerning the comparison with the MOVET outputs (developed by [12] and extracted from Figure 10 in their paper), despite some discrepancies in absolute terms, the estimates derived from the two satellite algorithms show a quite good agreement: R \(\sim\)62%, in the period 2000-2013,  
Figure 11: Spatial distribution of flaring sites detected by RST-FLARE (black dots), in the period 2000–2016 and VNF (red crosses), for the years 2012–2016. The yellow circles highlight the match between detected areas. Figure 12: Annual gas flared volumes computed for the Niger Delta region by RST-FLARE, based on OPEC (blue line) and EIA (pink line) sources. MOVET, adapted from [12] and VNF estimates (black dotted line and green line, respectively) are also shown. The solid grey line refers to the data independently provided by NNPC. between MOVET and RST-FLARE based on OPEC source; R \(\sim\)86%, in the period 2005-2013, when EIA-based RST-FLARE curve is taken into account. A high correlation (\(\sim\)95%) was found when RST-FLARE estimates were compared with the VNF ones, in the period 2012-2016. In this case, it is very interesting to note that both satellite algorithms highlighted a similar rate in reduction of the emitted volumes of gas flared, but with RST-FLARE absolute values almost double than the VNF ones. When the above mentioned satellite products were compared, each one in its corresponding temporal range, with the trend of values published by the NNPC (solid gray line in Figure 12), a reasonably close correspondence was found: \(\sim\)65% and \(\sim\)88% for OPEC and EIA-based RST-FLARE products (in 2000-2016 and 2005-2016, respectively), 66% for MOVET (2000-2013) and 88% for VNF (2012-2016). In Table 4 the biases between NNPC values and the analyzed satellite products are reported. Analyzing the errors in Table 4, RST-FLARE seems to offer good performances when compared to both MOVET and VNF. A mean bias in between \(\sim\)16% and \(\sim\)20% is committed in the annual volumes computation, when EIA and OPEC based models are employed, against the \(\sim\)34% and \(\sim\)25% of MOVET and VNF. RST-FLARE models are also the ones offering the best results in terms of minimum bias which, for both configurations, remains \(<\)1%. On the other hand, as far as the maximum error is considered, VNF seems the best method, assuring an error never higher than 43%. Besides, as far as the whole time period is considered, according to the NNPC data, a total of 270.7 BMC of gas was flared between 2000-2013 in the Niger Delta states. In the same period, the volumes computed by RST-FLARE, based on OPEC data, are equal to 246.7 BCM, 9% less than NNPC, while MOVET assesses 344.8 BCM, overestimating of about 27%. RST-FLARE showed even higher performances when the EIA-based model is used: in the period 2005-2013, 158.2 BCM of burned gas were estimated, only 2% higher than the NNPC value (i.e., 154.9 BCM), compared to the 197.5 BCM estimated by MOVET, resulting in an overestimation of about 34%. Similarly, with reference to 2012-2016 period, the RST-FLARE estimates of gas flared volumes (62.7 and 68.8 BCM) were about 6% and 16% (respectively for EIA and OPEC models) higher than the NNPC value (i.e., 59.3 BCM). For this period, the VNF overestimation respect to NNPC is \(\sim\)28%.