HDO/H2O ratio retrievals from GOSAT

[摘要] We report a new shortwave infrared (SWIR) retrieval of the column-averagedHDO/H₂O ratio from the Japanese Greenhouse Gases Observing Satellite(GOSAT). From synthetic simulation studies, we have estimated that theinferred δD values will typically have random errors between20‰ (desert surface and 30° solar zenith angle) and120‰ (conifer surface and 60° solar zenith angle). We findthat the retrieval will have a small but significant sensitivity to thepresence of cirrus clouds, the HDO a priori profile shape and atmospherictemperature, which has the potential of introducing some regional-scalebiases in the retrieval. From comparisons to ground-based column observationsfrom the Total Carbon Column Observing Network (TCCON), we find differencesbetween δD from GOSAT and TCCON of around −30‰ fornorthern hemispheric sites which increase up to −70‰ forAustralian sites. The bias for the Australian sites significantly reduceswhen decreasing the spatial co-location criteria, which shows that spatialaveraging contributes to the observed differences over Australia. The GOSATretrievals allow mapping the global distribution of δD and itsvariations with season, and we find in our global GOSAT retrievals theexpected strong latitudinal gradients with significant enhancements over thetropics. The comparisons to the ground-based TCCON network and the results ofthe global retrieval are very encouraging, and they show that δDretrieved from GOSAT should be a useful product that can be used tocomplement datasets from thermal-infrared sounder and ground-based networksand to extend the δD dataset from SWIR retrievals established from therecently ended SCIAMACHY mission.

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