Proxy methane retrievals from the ACOS project: Initial validation with TCCON and retrieval intercomparison

Recently, non-scattering methane retrievals using the 2nu3 methane band at 1.63 microns have been implemented into the pre-processor of the operational ACOS XCO2 retrieval scheme at JPL. Compared with TCCON ground-based stations, we observe a very good correlation with a slope of about 1.01 and typical standard devations of 15ppb (albeit with a small high bias of 25ppb). We will report on the retrieval performance, and its dependence on filtering criteria, with special focus on the potential of relaxing filters for the proxy method, which uses concurrently retrieved CO2 to minimize the impact of atmospheric scattering. We find that the data yield can be significantly enhanced without deteriorating the comparison against TCCON validation sites. This potentially allows for retrievals over snow and ice as well as nadir ocean soundings. We will also show comparisons against proxy and full-physics retrievals from the RemoteC algorithm.