Abstract
Optical gas imaging through multispectral cameras is a promising technique for mitigation of methane emissions through localization and quantification of emissions sources. While more advanced cameras developed in recent years have led to lower uncertainties in measuring gas concentrations, a systematic analysis of the uncertainties associated with leak rate estimation have been overlooked. We present a systematic categorization of the involved uncertainties with a focus on a theoretical analysis of projection uncertainties that are inherent to this technique. The projection uncertainties are then quantified using Large Eddy Simulation experiments of a point source release into the atmosphere. Our results show that while projection uncertainties are typically about 5% of the emission rate, low acquisition times and observation of the gas plume at small distances from the emission source (<10 m) can amount to errors of about 20%. Further, we found that acquisition times on the order of tens of seconds are sufficient to significantly reduce (>50%) the projection uncertainties. These findings suggest robust procedures on how to reduce projection uncertainties, however, a balance between other sources of uncertainty due to operational conditions and the employed instrumentation are required to outline more practical guidelines.
Highlights
We developed a theoretical analysis that led to two separate terms associated with the projection uncertainties, the covariance and mean velocity error terms
A simulated dataset generated through Large eddy simulations was used to quantify the significance of each of the projection uncertainty terms under varying imaging constraints of acquisition time, and downwind distance from the leak source
We found that low acquisition times and instantaneous estimates of the leak rate are prone to high projection uncertainties that can amount up to 20% of the emission rate
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Gas imaging includes capturing video images of methane plumes in the environment to quantify emission rates This technique involves the comparison of the at-sensor radiant energy in the IR part of the electromagnetic spectrum in the presence and absence of the gas plume [23,24]. Increased spatial and temporal resolution of imaging cameras translate into lower uncertainty in concentration measurement and velocity estimation which in turn leads to lower total uncertainty in leak quantification [27]. We formulate the projection uncertainties related to the transformation of gas imaging measurements into emission rates through a rigorous theoretical analysis that couples mass balance and spatial Reynolds decomposition. Program [31], our theoretical analysis stands true for video observations of any release of a conserved scalar into the environment
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