Title: A Compact Remote Sensing Lidar for High Resolution Measurements of Methane
Presenting Author: Haris Riris
Organization: NASA GSFC

Abstract:
We report on significant progress in advancing the technology for a laser transmitter at 1.65 µm that can measure methane with very high spatial resolution and sensitivity. Methane (CH4) is the second most important anthropogenic greenhouse gas with approximately 25 times the radiative forcing of 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 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. Natural sources of CH4 are dominated by wetland emissions in the tropics and Arctic and sub-Arctic boreal regions, with additional contributions from termites, ruminants, ocean biology, and a geological source of unknown significance. Natural sources account for about one-third of the emission total. The wetland source is particularly variable, linked to temperature, precipitation, and surface hydrological changes. In addition, the potential release of large amounts of stored organic carbon as CH4 and CO2 from thawing Arctic permafrost soils is a major cause for concern as a rapid, positive greenhouse gas/climate feedback. Large but greatly uncertain amounts of CH4 are sequestered as gas hydrates in shallow oceans and permafrost soils, which are also subject to potential rapid release. Although these boreal, phase-change driven sources are not yet estimated to be large, their potential magnitude and rapid growth dictate that measurement systems need to be put in place for early detection. Precise, seasonal measurements with coverage at high latitudes (i.e., in low sun to dark conditions) are required. The importance of this problem is clearly reflected in the IPCC report, the NASA Plan for a Climate-Centric Architecture, and the National Research Council Decadal Survey for Earth Science. This work is directly relevant to NASA's Earth Science Decadal Survey which called explicitly for cost-effective methane lidar technology. Our objectives are to: 1) Develop the technology for a compact, space-qualifiable laser transmitter for a lidar operating at 1.65 µm to enable Earth observation CH4 measurements. 2) Reduce the risk, cost, size, mass and volume of the CH4 lidar instrument by scaling the laser power of the existing laboratory breadboard. 3) Demonstrate and validate simultaneous, high sensitivity, methane and CO2 measurements using the proposed methane lidar and an operational CO2 lidar.