Simulation studies for a space-based CO₂ lidar mission

Abstract

A B S T R A C TWe report results of initial space mission simulation studies for a laser-based, atmospheric CO 2 sounder, which are based on real-time carbon cycle process modelling and data analysis. The mission concept corresponds to the Active Sensing of CO 2 Emissions over Nights, Days and Seasons (ASCENDS) recommended by the US National Academy of Sciences' Decadal Survey. As a pre-requisite for meaningful quantitative evaluation, we employ a CO 2 model that has representative spatial and temporal gradients across a wide range of scales. In addition, a relatively complete description of the atmospheric and surface state is obtained from meteorological data assimilation and satellite measurements. We use radiative transfer calculations, an instrument model with representative errors and a simple retrieval approach to quantify errors in 'measured' CO 2 distributions, which are a function of mission and instrument design specifications along with the atmospheric/surface state. Uncertainty estimates based on the current instrument design point indicate that a CO 2 laser sounder can provide data consistent with ASCENDS requirements and will significantly enhance our ability to address carbon cycle science questions. Test of a dawn/dusk orbit deployment, however, shows that diurnal differences in CO 2 column abundance, indicative of plant photosynthesis and respiration fluxes, will be difficult to detect.

Performance simulations for a spaceborne methane lidar mission

“…In order to estimate the global distribution of the precision of MERLIN's methane column concentration measurements, satellite observations by CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) [Winker et al, 2009] and MODIS (Moderate Resolution Imaging Spectrometer) [Schaaf et al, 2002] covering the whole year 2007 are used to constrain the simulation as closely as possible to real-world conditions, in an approach similar to the works of Kawa et al [2010]. Figure 1 illustrates this approach.…”

“…Occasional ambiguities by surface pressure uncertainties or the presence of near-surface clouds can be circumvented by accurate ranging (in the order of several meters), use of a high-resolution digital elevation model, and accurate pointing knowledge. Recent studies assessed the potential of spaceborne IPDA lidars: On board a low-polar orbit satellite, this method is able to provide column carbon dioxide or methane measurements with an accuracy (systematic uncertainty; bias) of better than 1%, a precision (random uncertainty; noise) of around 1%, and global coverage between 82°S and 82°N, largely independent of aerosol load or sunlight [Dufour and Bréon, 2003;Ehret and Kiemle, 2005;Ehret et al, 2008;Amediek et al, 2009;Kawa et al, 2010;Kiemle et al, 2011]. First airborne IPDA lidar deployments recently corroborated the studies' results [Abshire et al, 2014].…”

Global CO2 distributions over land from the Greenhouse Gases Observing Satellite (GOSAT)

“…[11] The modeled X CO2 data used in the intercomparison are based on the Goddard Space Flight Center parameterized chemistry and transport model, which is driven by real-time analyzed meteorological fields from the Goddard Global Modeling and Assimilation Office, version GEOS-5, and uses biospheric fluxes produced from the Carnegie-AmesStanford-Approach, which incorporate biomass burning from the Global Fire Emissions Database (PCTM/GEOS-5/ CASA-GFED), as well as oceanic and anthropogenic CO 2 flux estimates, as described by Kawa et al [2004Kawa et al [ , 2010. The model resolution is 1 Â 1.25 with 28 vertical levels and hourly output.…”

The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence

“…3 Of particular importance are higher order effects such as collisional narrowing, speeddependent effects and line mixing which are yet to be incorporated into the vast majority of atmospheric retrievals which often employ the Voigt line profile. These effects will play an even greater role in next generation, active sensing missions [4][5][6][7][8][9][10][11] (including NASA's Active Sensing of CO 2 Emissions over Nights Days and Seasons, ASCENDS) where individual transitions in the near-infrared spectral region will be interrogated rather than entire bands, and where precise measurements of CO 2 concentrations will require exquisite knowledge of the spectral line shape.…”