Title: Measuring Methane from space and airborne platforms
Presenting Author: Haris Riris
Organization: NASA GSFC
Co-Author(s): Kenji Numata, Jianping Mao, Stewart Wu, Molly Fahey, Brayler Gonzalez, Michael Rodriguez, Stan Scott, and Xiaoli Sun

Abstract:
The global and regional quantification of methane fluxes and identification of its sources and sinks has been highlighted as one of the goals of the 2017 Earth Science Decadal Survey. Detecting methane from space with an active (laser) remote sensing instrument presents several unique technology and measurement challenges. The instrument must have a single frequency, narrow-linewidth light source, and photon-sensitive detector at the right spectral region to make continuous measurements from orbit, day and night, all seasons and at all latitudes. It must have a high signal to noise ratio and must be relatively immune to biases from aerosol/cloud scattering, spectroscopic and meteorological data uncertainties, and instrument systematic errors. The technology needed for a spaceborne mission is currently being developed by NASA and industry. At Goddard Space Flight Center (GSFC), we have developed an airborne instrument to measure methane. Our instrument is a nadir-viewing lidar that uses Integrated Path Differential Absorption (IPDA), to measure a methane vibration-rotational line near 1.65 µm that is relatively free of interferences from other trace gases. We sample the absorption line using multiple wavelengths from a narrow linewidth laser source and a sensitive photodetector. This measurement approach provides maximum information content about the vertical distribution of CH4, minimum bias, and sensitivity to atmospheric temperature uncertainty in XCH4 retrieval. However, technical and measurement challenges remain. In this paper, we will review our progress to date and discuss the technology challenges, options and tradeoffs to measure methane from space.