Calibration of Digital Holographic Camera for Bubble Gas Volumetric Flux Measurements

This study is aimed at developing and verifying a method that uses a digital holographic camera to measure the gas volumetric flux, which is relevant for the monitoring of gas emissions, in particular methane in the Arctic seas. The method is based on the analysis of histograms of cross-sectional areas of gas bubbles and their velocities obtained from holographic data. The result of the study is the determination of a constant calibration factor k = 2, taking into account the geometric factor of the camera and the deformation of the bubbles. The coefficient is determined in laboratory conditions, taking into account the area of the gas-generating site of a bubble generator simulating a gas flare. It is found that k remains stable in a wide range of a gas volumetric flux from 5 × 10⁻⁴ m³·m⁻²·s⁻¹ to 15 × 10⁻⁴ m³·m⁻²·s⁻¹ that limits the applicability of a working formula. Verification of the method in the field conditions of the Arctic expedition showed good agreement with the data obtained by the standard trap method: the discrepancy was only 5%. It was shown that the method is applicable for quantitative assessment of weak gas emissions, in particular methane, in the Arctic seas, where the measured volumetric fluxes are orders of magnitude lower than the established upper limit of the method.