Column CO2 Measurements with Intensity-Modulated Continuous-Wave Lidar System During the ASCENDS 2014 Summer Field Experiment

Abstract:

This paper presents an overview of the ASCENDS 2014 flight campaign results of an intensity-modulated continuous-wave (IM-CW) lidar system operating at 1.57 µm for measurements of column CO₂ over a wide variety of geographic regions. The 2007 National Research Council’s Decadal Survey of Earth Science and Applications from Space recommended Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) as a mid-term, Tier II, space mission to address global sources, sinks, and transport of atmospheric CO₂. As part of the development of a capability for the NASA ASCENDS mission, NASA Langley Research Center (LaRC) and Exelis, Inc. have been collaborating to develop, demonstrate and mature the IM-CW lidar approach for measuring atmospheric column CO₂ mixing ratios from a space platform using the integrated path differential absorption (IPDA) lidar technique with preferential weighting of the CO₂ measurements to the mid to lower troposphere. The Multi-Functional Fiber Laser Lidar (MFLL), a system developed as a technology demonstrator for the ASCENDS mission, has been used to demonstrate high precision column CO₂ retrievals from various aircraft platforms. The MFLL operates using a novel IM-CW IPDA approach to make simultaneous CO₂ and O₂ column measurements in the 1.57-micron and 1.26-micron spectral regions, respectively, to derive the column-average CO₂ dry-air mixing ratios. Measurements from the 2014 summer field experiment focused on advancing CO₂ & O₂ measurement technologies under day and night conditions in realistic environments, assessing CO₂ emissions over large metropolitan areas, observing and evaluating CO₂ drawdown and diurnal trends over large agricultural regions, obtaining reflectance data and CO₂ & O₂ measurements over rough ocean surfaces with high surface wind speeds (~10 m/s), and carrying out CO₂ & O₂ intercomparisons with OCO-2 and GOSAT over the western United States. Initial results from MFLL for the aforementioned flight campaign objectives will be presented where precision and accuracy of the CO₂ and O₂ optical depths, as well as the column-average CO₂ mixing ratios, will be evaluated with respect to in-situ aircraft measurements of CO₂ and meteorological state parameters.