Project Funding: 2015 - 2018

NRA: 2014 NASA: OCO-2 Science Team for the OCO-2 Mission   

Funded by NASA

Abstract:
Proper interpretation of spectral observations from the Orbiting Carbon Observatory-2 (OCO-2) requires state-of-the-art knowledge of the carbon dioxide and oxygen line parameters. Prior to launch, extensive new laboratory studies were performed to improve precisions and accuracies of the required molecular line parameters for CO2 (at 2.1 and 1.6 µm) and O2 (at 0.76 µm). Nevertheless, validations using ground-based (TCCON) atmospheric observations indicated that important band-to-band inconsistencies will appear in the high air-mass OCO-2 retrievals. This proposal will continue the effort to resolve this problem by improving spectroscopic knowledge of molecular line shapes for O2 A-band transitions using three types of laboratory spectra recorded through a range of pressures and temperatures. To achieve this goal, we simultaneously use data from three different types of spectrometers to retrieve the O2 line parameters with customized multi-spectral fitting software. This collaborative effort has the advantage of three existing laboratory datasets: i) Fourier-transform spectra (FTS) at different temperatures (140 - 296 K) and spectra at room temperature from ii) Cavity Ring Down (CRDS) and iii) Photo Acoustic (PAS) at high pressures. This effort also will extend the capabilities of these CRDS and PAS instruments to collect additional spectra at temperatures throughout the atmospheric range (220 - 350 K). The CRDS and PAS data sets are 'background free' and provide the capability to extract non-resonant (continuum induced absorption or CIA) absorption from high density gases. Thus, this is a focused effort to forge a common analytic solution that takes advantage of the most favorable aspects for each technique. The key objective is to obtain the best O2 line positions, intensities, pressure-broadening coefficients (widths and pressure-induced shifts) and their temperature dependences that are internally consistent. This will be achieved using a multi-spectral fitting program Labfit from D. Chris Benner modified to retrieve simultaneously all these parameters using all the FTS, CRDS and PAS data at the same time. The Labfit program can fit a variety of lineshape function including the Dicke narrowed lineshape that has been effective for modeling O2 A-band spectra. This is the strategy needed to produce a single, high fidelity oxygen spectroscopy model for OCO-2.