US environmental group wins millions to develop methane-monitoring satellite

Twenty-Five-Fold Reduction in Measurement Uncertainty for a Molecular Line Intensity

“…For example, the high-resolution JAXA Greenhouse Gases Observing Satellite (GOSAT) [10] and NASA Orbiting Carbon Observatory (OCO) [11] passive remote sensing missions have, for more than a decade, relied upon accurate spectroscopic forward models of carbon dioxide (CO 2 ) and molecular oxygen (O 2 ) to retrieve CO 2 column densities: the measurement target being a precision of 1 μmol/mol, or approximately 0.3 % of the nominal mean column density [12–14]. Additionally, monitoring global trends in atmospheric methane (CH 4 ) [15–18] and performing point-source attribution [19] currently motivates laboratory research into accurate first-principles models in congested spectral regions [20, 21], and open-path dual-comb spectroscopy has achieved the following low relative instrumental variations for mole fractions at 30 s of integration: 0.14 % for CO 2 , 0.35 % for CH 4 , and 0.40 % for water (H 2 O) [22]. Consequently, reference values for the absorption cross-sections (derived from the oscillator strengths) of these and many more molecules (e.g., [23]) must be known with sufficiently low relative uncertainty (≤0.1 %) to ensure accurate retrievals from highly precise instruments.…”