Abstract
The objective was to validate the carbon monoxide (CO) total column product inferred from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) full-mission (2003–2011) short-wave infrared (SWIR) nadir observations using the Beer InfraRed Retrieval Algorithm (BIRRA). Globally distributed Network for the Detection of Atmospheric Composition Change (NDACC) and Total Carbon Column Observing Network (TCCON) ground-based (g-b) measurements were used as a true reference. Weighted averages of SCIAMACHY CO observations within a circle around the g-b observing system were utilized to minimize effects due to spatial mismatch of space-based (s-b) and g-b observations, i.e., disagreements due to representation errors rather than instrument and/or algorithm deficiencies. In addition, temporal weighted averages were examined and then the unweighted (classical) approach was compared to the weighted (non-classical) method. The delivered distance-based filtered SCIAMACHY data were in better agreement with respect to CO averages as compared to square-shaped sampling areas throughout the year. Errors in individual SCIAMACHY retrievals have increased substantially since 2005. The global bias was determined to be in the order of − 10 parts per billion in volume (ppbv) depending on the reference network and validation strategy used. The largest negative bias was found to occur in the northern mid-latitudes in Europe and North America, and was partly caused by insufficient a priori estimates of CO and cloud shielding. Furthermore, no significant trend was identified in the global bias throughout the mission. The global analysis of the CO columns retrieved by the BIRRA shows results that are largely consistent with similar investigations in previous works.
Highlights
Obtaining space-based (s-b) measurements of the state of Earth’s atmosphere is costly compared to many other atmospheric research activities
The SCIAMACHY observations within various-sized areas around two the NDACC and Total Carbon Column Observing Network (TCCON) g-b sites, namely Bremen and Izana, are compared in Figure 6 and the results demonstrate that the adequate spatial and temporal range of averaging depends on the precision of the s-b observations at a specific site
The results demonstrate that some fraction of the SCIAMACHY xCO bias seen at Garmisch and Zugspitze is likely to be an effect of spatial mismatch, i.e., representation error, and should not solely be considered as a retrieval or instrument flaw
Summary
Obtaining space-based (s-b) measurements of the state of Earth’s atmosphere is costly compared to many other atmospheric research activities. Once the instruments needed to take these measurements are in orbit, thorough verification and validation of the delivered data is required. Considerable efforts have been invested in establishing a ground-based (g-b) validation infrastructure for atmospheric composition, temperature, cloud, and aerosol data acquired by satellite-based remote sensing instruments. The Environmental Satellite (ENVISAT) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) Instrument. The satellite comprised 10 instruments with the SCIAMACHY, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and Global Ozone Monitoring by Occultation of Stars (GOMOS) dedicated to studying the Earth’s atmosphere. The SCIAMACHY was an ultra-violet (UV) to short-wave infrared (SWIR, 1.4–3 μm) absorption spectrometer that observed the scattered and reflected solar spectral radiance transmitted through the atmosphere [2]
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