Towards the Optimization of TanSat-2: Assessment of a Large-Swath Methane Measurement

To evaluate the potential of an upcoming large-swath satellite for estimating surface methane (CH₄) fluxes at a weekly scale, we report the results from a series of observing system simulation experiments (OSSEs) that use an established modeling framework that includes the GEOS-Chem 3D atmospheric transport model and an ensemble Kalman filter. These experiments focus on the sensitivity of CH₄ flux estimates to systematic errors ((Formula presented.)) and random errors ((Formula presented.)) in the column average methane (XCH₄) measurements. Our control test (INV_CTL) demonstrates that with median errors ((Formula presented.) = 1.0 ± 0.9 ppb and (Formula presented.) = 6.9 ± 1.6 ppb) in XCH₄ measurements over a 1000 km swath, global CH₄ fluxes can be estimated with an accuracy of 5.1 ± 1.7%, with regional accuracies ranging from 3.8% to 21.6% across TransCom sub-continental regions. The northern hemisphere mid-latitudes show greater reliability and consistency across varying (Formula presented.) and (Formula presented.) levels, while tropical and boreal regions exhibit higher sensitivity due to limited high-quality observations. In (Formula presented.) -sensitive regions, such as the North American boreal zone, expanding the swath width from 1000 km to 3000 km significantly reduces discrepancies, while such adjustments provide limited improvements for (Formula presented.) -sensitive regions like North Africa. For TanSat-2 mission, with its elliptical medium Earth orbit and 1500 km swath width, the global total estimates achieved an accuracy of 3.1 ± 2.2%. Enhancing the swath width or implementing a dual-satellite configuration is proposed to further improve TanSat-2 inversion performance.