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 104 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.
Highlights
Retrieving atmospheric trace gas concentrations from infrared satellite observations can be an expensive process, especially when implementing an inverse method such as optimal estimation (Rodgers, 2000)
This paper presents a new method for rapidly retrieving trace gas abundances as applied towards estimating total vertical column amounts of carbonyl sulfide (OCS)
Physical parameters that influence the spectral observations over the wave number range used for OCS are directly accounted for by jointly retrieving them along with OCS
Summary
Retrieving atmospheric trace gas concentrations from infrared satellite observations can be an expensive process, especially when implementing an inverse method such as optimal estimation (Rodgers, 2000) In this approach, a radiative transfer model (RTM) describing the physics of light propagating through the atmosphere is iteratively evaluated for every pixel while comparing the model spectrum of the estimate to the measurement. Constraints upon the solution are generally required when estimating more parameters than are independently represented in the observation While such methods approach theoretical limits of detectability, iteratively evaluating the RTM can be such a time-consuming process that the retrieval fails to keep pace with data acquisition. Atmospheric OCS estimates from IASI observations throughout 2014 are used as a case study for this new rapid retrieval method because OCS is an important trace gas for understanding the global sulfur cycle, is currently poorly modelled, and is at the edge of detectability with nadirviewing instruments like IASI. Previous work suggests that OCS is the primary source of stratospheric sulfates during periods of low volcanic activity (Notholt et al, 2003)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
