Title: Methane measurements from space: technical challenges and status
Presenting Author: Haris Riris
Organization: NASA GSFC
Co-Author(s): Kenji Numata (GSFC), Stewart Wu (GSFC), Bryan Duncan (GSFC), Jianping Mao (UMD/GSFC), Mike Rodriguez (Sigma Space/GSFC), Brayler Gonzalez (GSFC), Molly Fahey (GSFC), Randy Kawa (GSFC), Stan Scott (GSFC), Anthony Yu (GSFC), Mark Stephen (GSFC), Bill Hasselbrack (Sigma Space/GSFC)

Abstract:
Atmospheric methane (CH4) is the second most important anthropogenic greenhouse gas with approximately 25 to 100 times the radiative forcing of carbon dioxide (CO2) per molecule. CH4 also contributes to pollution in the lower atmosphere through chemical reactions leading to ozone production. Yet, lack of understanding of the processes that control CH4 sources and sinks and its potential release from stored carbon reservoirs contributes significant uncertainty to our knowledge of the interaction between carbon cycle and climate change that challenges our ability to make confident projections of future climate. At Goddard Space Flight Center (GSFC) we have been developing the technology needed to remotely measure CH4 from orbit, using lasers. Our concept for a CH4 lidar is a nadir viewing instrument that uses the strong laser echoes from the Earth's surface to measure CH4. The instrument has a tunable, narrow-frequency light source and photon-sensitive detector to make continuous measurements from orbit, in sunlight and darkness, at all latitudes and can be relatively immune to errors introduced by scattering from clouds and aerosols. Our measurement technique uses Integrated Path Differential Absorption (IPDA), which measures the absorption of laser pulses by a trace gas when tuned to a wavelength coincident with an absorption line. We have demonstrated ground and airborne CH4 measurements with a different transmitters and a sensitive receiver. In this paper we will review our results to date and discuss the technology options to scale the laser power to space.