Single-blind detection, localization, and quantification of methane emissions using continuous path-integrated column measurements

Abstract

Path-integrated column measurements with a laser-absorption-based measurement system have been used to detect, locate, and quantify methane emissions from a series of single-blind controlled releases with no prior knowledge of timing, locations, or release rates. System performance was evaluated against metrics defined in the Continuous Monitoring Protocol established by the Colorado State University Methane Emissions Technology Evaluation Center (METEC). This protocol allows more direct comparison of system performance between disparate measurement technologies and is transferable to any test facility. To the authors’ knowledge, this work represents the first time the protocol has been directly applied at a test facility other than METEC. This experiment differs from similar tests where releases were conducted from equipment units at fixed locations at METEC by instead conducting releases at random locations anywhere within the central 0.18 km2 of a 0.35 km2 unobstructed test site. The releases were much shorter in duration than those conducted in similar testing at METEC. The system detected 25 of 42 releases with metered rates of 0.17–2.15 kg h−1. The minimum detected emissions rate was 0.22 kg h−1, and the system demonstrated a 100% detection rate for releases ≥0.65 kg h−1 when average wind speed was <5 m s−1. The test site was subdivided into 20 boxes (109 m × 83 m each), and the correct release box was identified in 9 cases, another 9 detections were localized to an adjacent box, and the remaining 7 were attributed elsewhere within the field. The average estimated emission rate bias was −6.1%. The 90% detection limit was 0.89 kg h−1, while the wind-normalized detection limit was 0.44 (kg h−1) (m s−1)−1.