IASI's sensitivity to near-surface carbon monoxide (CO): Theoretical analyses and retrievals on test cases. (March 2017)

• Record Type: Journal Article
• Authors: Bauduin, Sophie; Clarisse, Lieven; Theunissen, Michael; George, Maya; Hurtmans, Daniel; Clerbaux, Cathy; Coheur, Pierre-François
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 189(2017)
• Page Start: 428
• Page End: 440
• Publication Date: 2017-03
• Subjects: IASI -- Carbon monoxide -- Thermal contrast -- Vertical sensitivity -- Planetary boundary layer; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2016.12.022
• Languages: English
• ISSNs: 0022-4073

Abstract

Abstract: Separating concentrations of carbon monoxide (CO) in the boundary layer from the rest of the atmosphere with nadir satellite measurements is of particular importance to differentiate emission from transport. Although thermal infrared (TIR) satellite sounders are considered to have limited sensitivity to the composition of the near-surface atmosphere, previous studies show that they can provide information on CO close to the ground in case of high thermal contrast. In this work we investigate the capability of IASI (Infrared Atmospheric Sounding Interferometer) to retrieve near-surface CO concentrations, and we quantitatively assess the influence of thermal contrast on such retrievals. We present a 3-part analysis, which relies on both theoretical forward simulations and retrievals on real data, performed for a large range of negative and positive thermal contrast situations. First, we derive theoretically the IASI detection threshold of CO enhancement in the boundary layer, and we assess its dependence on thermal contrast. Then, using the optimal estimation formalism, we quantify the role of thermal contrast on the error budget and information content of near-surface CO retrievals. We demonstrate that, contrary to what is usually accepted, large negative thermal contrast values (ground cooler than air) lead to a better decorrelation between CO concentrations in the low and the high troposphere than large positive thermal contrast (ground warmer than the air). In the last part of the paper we use Mexico City and Barrow as test cases to contrast our theoretical predictions with real retrievals, and to assess the accuracy of IASI surface CO retrievals through comparisons to ground-based in-situ measurements. Highlights: The sensitivity of the IASI instrument to near-surface CO is analysed. 3-part analysis based on forward simulations and retrievals on real data. Impact of thermal contrast on the detection of surface CO enhancements is evaluated. Large negative thermal contrasts better decorrelate low and high tropospheric CO. Impact of thermal contrast on the retrieval accuracy is assessed.