Quantifying CH 4 point source emissions with airborne remote sensing: first results from AVIRIS-4

Abstract

Abstract. Atmospheric concentration of methane (CH4), a potent greenhouse gas, increased significantly since pre-industrial times, with anthropogenic emissions originating primarily from agriculture, fossil fuel sector and waste management. However, considerable uncertainties persist in the detection and quantification of anthropogenic CH4 emissions. In this study, we present first CH4 observations, plume detections and emission estimates from the new state-of-the-art Airborne Visible InfraRed Imaging Spectrometer 4 (AVIRIS-4), which participated in a blind controlled release experiment in September 2024 in southern France. We used an albedo-corrected matched filter to retrieve CH4 maps from the spectral images and estimated CH4 emission with the Integrated Mass Enhancement (IME) and Cross-Sectional Flux (CSF) methods. Our results demonstrate that AVIRIS-4 can reliably detect emissions as low as 5.5 kg CH4 h−1 under good weather conditions at low flight altitudes (< 1500 m) and 1.45 kg CH4 h−1 under ideal conditions. These low-altitude detection limits are substantially lower than published detection limits for the predecessor instrument AVIRIS-NG, which were in the order of 10–16 kg CH4 h−1 under comparable conditions. While AVIRIS-4 provides highly accurate CH4 maps at < 0.5 m resolution, emission estimation is limited by the accuracy of the effective wind speed, whose uncertainty and natural variability contribute substantially to the overall uncertainty. Using wind speed at source height performs well for small releases (below 20 kg CH4 h−1) (rRMSE =1.065; rMBE =0.361) and overall (rRMSE =0.702; rMBE =−0.204). Using literature-derived effective wind speeds improves the apparent fit between estimated and reported CH4 emissions, but degrades performance both in overall agreement (rRMSE =2.098; rMBE =0.964) and for low-emission events (rRMSE =2.367; rMBE =1.711). Interestingly, the high spatial resolution makes it possible to retrieve the cast shadow of the CH4 plume, which can be used to estimate source and plume height, and could provide an approach for better constraining the height-dependency of the effective wind speed. On the bottom line, the controlled release experiment provides critical insights into the sensor's capabilities and guides further improvements to detect and quantify low intensity sources in the fossil fuel and waste management sectors, with implications for more accurate global greenhouse gas monitoring.