Fast retrievals of tropospheric carbonyl sulfide with IASI

Abstract

Abstract. Iterative retrievals of trace gases, such as carbonyl sulfide (OCS), from satellites can be exceedingly slow. The algorithm may even fail to keep pace with data acquisition such that analysis is limited to local events of special interest and short time spans. With this in mind, a linear retrieval scheme was developed to estimate total column amounts of OCS at a rate roughly 10 4 times faster than a typical iterative retrieval. This scheme incorporates two concepts not utilized in previously published linear estimates. First, all physical parameters affecting the signal are included in the state vector and accounted for jointly, rather than treated as effective noise. Second, the initialization point is determined from an ensemble of atmospheres based on comparing the model spectra to the observations, thus improving the linearity of the problem. All of the 2014 data from the Infrared Atmospheric Sounding Interferometer (IASI), instruments A and B, were analysed and showed spatial features of OCS total columns, including depletions over tropical rainforests, seasonal enhancements over the oceans, and distinct OCS features over land. Error due to assuming linearity was found to be on the order of 11 % globally for OCS. However, systematic errors from effects such as varying surface emissivity and extinction due to aerosols have yet to be robustly characterized. Comparisons to surface volume mixing ratio in situ samples taken by NOAA show seasonal correlations greater than 0.7 for five out of seven sites across the globe. Furthermore, this linear scheme was applied to OCS, but may also be used as a rapid estimator of any detectable trace gas using IASI or similar nadir-viewing instruments.

Reviews and Syntheses: Carbonyl Sulfide as a Multi-scale Tracer for Carbon and Water Cycles

“…spatial smoothing has been applied to TES and MIPAS data. The IASI spatial patterns are of resolution 0.5° × 0.5° and are extracted from Vincent and Dudhia (2017). Missing data are represented by white areas in panels (a) and (b) and by gray areas in panel (c).…”

“…Currently, global OCS concentrations have been retrieved from a few satellite instruments, including NASA's TES (Kuai et al, 2014), the Canadian Space Agency's Atmospheric Chemistry ExperimentFourier Transform Spectrometer (ACE-FTS) (Boone et al, 2005), the European Space Agency's MIPAS (Glatthor et al, 2017) and the Infrared Atmospheric Sounding Interferometer (IASI) (Vincent and Dudhia, 2017). Among these instruments, TES and IASI are nadir-viewing instruments (i.e.…”

Sampling bias adjustment for sparsely sampled satellite measurements applied to ACE-FTS carbonyl sulfide observations

“…OCS with its atmospheric variability in the stratosphere and upper troposphere limited to large spatial (100s of km) and temporal (i.e., seasons) scales (Barkley et al, 2008) provides an ideal tracer to investigate and demonstrate the sampling bias adjustment method. Note that the method would not work in the presented form (i.e., with a relatively simple regression model that is reasonably well determined by the data) for an OCS data product reflecting the lower tropospheric and boundary layer variability with complex regional patterns and to some extent distinct day-night differences such as the Infrared Atmospheric Sounding Interferometer (IASI) tropospheric OCS product described by Vincent and Dudhia (2017).…”

Scientific Communities Striving for a Common Cause: Innovations in Carbon Cycle Science

“…OCS measurements have been retrieved from satellite spectrometers that were already launched, but no OCS-specific space-based sensors are planned for the future. Several satellite products report OCS measurements in the upper troposphere and stratosphere: NASA's TES (Kuai et al 2014), ESA's MIPAS (Glatthor et al 2017) and IASI (Vincent and Dudhia 2017)…”