# Measuring Gas Flaring in Russia with Multispectral VIIRS Nightfire
## 4 Discussion
### Effect of Gas Processing
Note that three ground flare stacks and one vertical flare stack in close proximity are aggregated into a single Nightfire detection. (**b**) Plot Nightfire estimates (\(x\)-axis, BCM) with reported flaring data (\(y\)-axis, BCM) [47, 53, 54, 55, 56, 57, 58]. Nightfire estimates are a sum of all detected flaring volumes within the Vankor field. Note the difference in scale for the axes. (**c**) Daily flare dashboard of the flare stack cluster at Vankor southern oil dehydration and desalting unit as shown in (**a**), containing 1  
reported quarterly gas flaring volumes in 2012 and 2013 [58]. It is evident that in 2012-2013, Nightfire estimates (1.5-1.6 BCM) are four to five times lower than the reported flaring volumes. However, controlled field experiments have shown good agreement between Nightfire estimates and flow meter measurements for a gas flare stack burning as high as an equivalent of approximately 0.4 BCM of natural gas per year (i.e., at least five times lower than the reported flaring at major oil treatment units of the Vankor field in 2012-2014) [25]. It is also worth noting that, due to the high APG over-limit flaring environmental fee multiplier in Russia described in Section 1.1, there is no practical reason for oil companies to overstate their flaring volumes, and Vankor oil field was commissioned in 2009 and thus have been subject to the increased environmental taxation since 2012. The case of the Vankor field thus leads to an assumption that VIIRS Nightfire tends to significantly underestimate the largest observed gas flares. The reason for this is a matter for further research. Supposedly, it may be attributed to either the application of a logarithmic scale to the area of the observed flare (see Equation (4) in Section 2.5) in the Nightfire algorithm or to registering the local maximum spectral radiance only of the brightest SWIR channel pixel in a single observation, while in fact the largest flares may produce a considerable \"halo\" in surrounding VIIRS SWIR pixels or be frequently observed as split in neighboring pixels; the latter was also observed in a controlled field test environment [25]. In addition, underestimation of the largest flares may in turn lead to an overestimation of the smaller and persistent gas flares, as the Nightfire-estimated sum of \(RH^{\prime}\) is correlated linearly with Cedigaz's estimated national-level flaring volumes for calibration, as described in Section 2.5. As a grace period exists for newly commissioned oil fields (greenfields) in Russia (see Section 1.1), major fields in remote regions that have been coming into industrial operation in recent years, tend to follow the pattern of the Vankor oil field, with almost non-existent gas utilization in the first few years of commercial operation followed by the completion of the gas processing infrastructure by the end of the grace period, meeting 95% APG utilization requirements and showing moderate flaring levels afterwards. For reference, the Nightfire annual flaring estimate for the Vankor field dropped from 1.6 BCM in 2012-2013 to 0.1 BCM in 2017-2020.