Detectability of CO2 flux signals by a space-based lidar mission

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 120 (2015): 1794–1807, doi:10.1002/2014JD022483.
Satellite observations of carbon dioxide (CO2) offer novel and distinctive opportunities for improving our quantitative understanding of the carbon cycle. Prospective observations include those from space-based lidar such as the active sensing of CO2 emissions over nights, days, and seasons (ASCENDS) mission. Here we explore the ability of such a mission to detect regional changes in CO2 fluxes. We investigate these using three prototypical case studies, namely, the thawing of permafrost in the northern high latitudes, the shifting of fossil fuel emissions from Europe to China, and changes in the source/sink characteristics of the Southern Ocean. These three scenarios were used to design signal detection studies to investigate the ability to detect the unfolding of these scenarios compared to a baseline scenario. Results indicate that the ASCENDS mission could detect the types of signals investigated in this study, with the caveat that the study is based on some simplifying assumptions. The permafrost thawing flux perturbation is readily detectable at a high level of significance. The fossil fuel emission detectability is directly related to the strength of the signal and the level of measurement noise. For a nominal (lower) fossil fuel emission signal, only the idealized noise-free instrument test case produces a clearly detectable signal, while experiments with more realistic noise levels capture the signal only in the higher (exaggerated) signal case. For the Southern Ocean scenario, differences due to the natural variability in the El Niño–Southern Oscillation climatic mode are primarily detectable as a zonal increase.
This material is based upon work supported by the National Aeronautics and Space Administration under grant NNX08AJ92G issued through the Research Opportunities in Space and Earth Sciences Carbon Cycle Science program and by Jet Propulsion Laboratory subcontract 1442785 as well as the ASCENDS Science Requirements Definition Team. S. Doney acknowledges support from U.S. National Science Foundation (AGS-1048827). K. Schaefer acknowledges support from the National Oceanic and Atmospheric Administration under grant NA09OAR4310063 and from the National Aeronautics and Space Administration under grant NNX10AR63G.
2015-09-11