Remote sensing of methane point sources with the MethaneAIR airborne spectrometer

Abstract. The MethaneAIR imaging spectrometer was originally developed as an airborne demonstrator of the MethaneSAT satellite mission. MethaneAIR enables accurate methane concentration retrievals from high spectral resolution measurements in the 1650-nm methane absorption feature at a nominal spatial sampling of 5x25 m. In this work, we present a computationally-efficient data processing chain optimized for the detection and quantification of methane plumes with MethaneAIR. It involves the retrieval of methane concentration enhancements (ΔXCH₄) with the high-precision matched-filter retrieval, which is applied to 1650-nm retrievals for the first time. Methane plumes are detected through visual inspection of the resulting ΔXCH₄ maps. Flux rates are estimated from the detected plumes using the integrated mass enhancement (IME) method. The evaluation of the proposed methods included comparisons with simulated plumes, with existing plume retrieval and quantification methods for MethaneAIR, and with controlled methane releases. We applied our processing chain to MethaneAIR at-sensor radiance datasets acquired over the Permian Basin during flights in 2021 and 2023, which resulted in the detection of hundreds of point sources above 100–200 kg/h, with a conservative detection limit around 120 kg/h. Our results show the consistency of MethaneAIR's ΔXCH₄ matched-filter retrievals, and their potential for the detection and quantification of methane point sources across large areas.