CHARM-F—a new airborne integrated-path differential-absorption lidar for carbon dioxide and methane observations: measurement performance and quantification of strong point source emissions

Abstract

The integrated-path differential-absorption lidar CHARM-F (CO and CH Remote Monitoring-Flugzeug) was developed for the simultaneous measurement of the greenhouse gases CO and CH onboard the German research aircraft HALO (High Altitude and Long Range Research Aircraft). The purpose is to derive the weighted, column-averaged dry-air mixing ratios of the two gases with high precision and accuracy between aircraft and ground or cloud tops. This paper presents the first measurements, performed in the spring of 2015, and shows performance analyses as well as the methodology for the quantification of strong point sources applied on example cases. A measurement precision of below 0.5% for 20 km averages was found. However, individual measurements still show deviations of the absolute mixing ratios compared to corresponding data from in situ profiles. The detailed analysis of the methane point source emission rate yields plausible results (26±3 m/min or 9.2±1.15 kt CH yr), which is in good agreement with reported numbers. In terms of CO, a power plant emission could be identified and analyzed.

Potential of Spaceborne Lidar Measurements of Carbon Dioxide and Methane Emissions from Strong Point Sources

“…The main advantage is a considerable gain in measurement accuracy and precision, while keeping the instrument at an affordable size. More details on the IPDA methodology are found in [18,[24][25][26]. We focus here on particularities of the method regarding plume measurements from an air-or spacecraft, and apply the formalism introduced by [25].…”

“…We limit our Lidar sizing analysis to pulsed, direct detection systems with two wavelengths (on-and offline), using knowledge gained during the planning and design phase of airborne [18] and …”

“…The dependency on enough sunlight is a serious limitation to passive sensors operating in the NIR and SWIR spectral domains, mainly in the Northern Hemisphere, where substantial emissions occur particularly in winter, but also in other seasons. In contrast, Integrated Path Differential Absorption (IPDA) Lidar measurements are largely immune to these limitations and initial results from airborne IPDA-Lidar applications look promising [17,18]. Installed on-board an aircraft or a satellite, such an active remote sensor uses laser signals scattered back from Earth's surface to measure the weighted vertical column concentrations (XCO 2 , XCH 4 ) with a small and well-defined field-of-view.…”

“…Installed on-board an aircraft or a satellite, such an active remote sensor uses laser signals scattered back from Earth's surface to measure the weighted vertical column concentrations (XCO 2 , XCH 4 ) with a small and well-defined field-of-view. A single plume overpass in the lee of the point source, within distances between a few hundred meters and a few km away from the source, yields measurements of the XCO 2 or XCH 4 plume enhancement which is directly proportional to the emission rate [18]. The plume has to be sampled in its full cross sectional extension but need not necessarily be overflown in direction perpendicular to its alignment along the wind.…”

“…First airborne IPDA Lidar measurements of individual CO 2 and CH 4 plumes from power plants and a coalmine ventilation shaft were reported recently, and emission rates could successfully be estimated from the measured column concentration enhancements generated by the plumes [17,18]. It is appropriate now to assess the feasibility of global Lidar observations of point sources that could complement the current and future observation systems, and to discuss the implications for a novel space-borne IPDA Lidar which goes beyond the systems currently being designed and developed [19][20][21][22][23].…”