Comparison of improved Aura Tropospheric Emission Spectrometer CO<sub>2</sub> with HIPPO and SGP aircraft profile measurements

Abstract

Abstract. Thermal infrared radiances from the Tropospheric Emission Spectrometer (TES) between 10 and 15 μm contain significant carbon dioxide (CO2) information, however the CO2 signal must be separated from radiative interference from temperature, surface and cloud parameters, water, and other trace gases. Validation requires data sources spanning the range of TES CO2 sensitivity, which is approximately 2.5 to 12 km with peak sensitivity at about 5 km and the range of TES observations in latitude (40° S to 40° N) and time (2005–2011). We therefore characterize Tropospheric Emission Spectrometer (TES) CO2 version 5 biases and errors through comparisons to ocean and land-based aircraft profiles and to the CarbonTracker assimilation system. We compare to ocean profiles from the first three Hiaper Pole-to-Pole Observations (HIPPO) campaigns between 40° S and 40° N with measurements between the surface and 14 km and find that TES CO2 estimates capture the seasonal and latitudinal gradients observed by HIPPO CO2 measurements. Actual errors range from 0.8–1.8 ppm, depending on the campaign and pressure level, and are approximately 1.6–2 times larger than the predicted errors. The bias of TES versus HIPPO is within 1 ppm for all pressures and datasets; however, several of the sub-tropical TES CO2 estimates are lower than expected based on the calculated errors. Comparisons to land aircraft profiles from the United States Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) between 2005 and 2011 measured from the surface to 5 km to TES CO2 show good agreement with an overall bias of −0.3 ppm to 0.1 ppm and standard deviations of 0.8 to 1.0 ppm at different pressure levels. Extending the SGP aircraft profiles above 5 km using AIRS or CONTRAIL measurements improves comparisons with TES. Comparisons to CarbonTracker (version CT2011) show a persistent spatially dependent bias pattern and comparisons to SGP show a time-dependent bias of −0.2 ppm yr−1. We also find that the predicted sensitivity of the TES CO2 estimates is too high, which results from using a multi-step retrieval for CO2 and temperature. We find that the averaging kernel in the TES product corrected by a pressure-dependent factor accurately reflects the sensitivity of the TES CO2 product.

Bias assessment of lower and middle tropospheric CO<sub>2</sub> concentrations of GOSAT/TANSO-FTS TIR version 1 product

“…More in situ CO 2 data in the upper atmosphere in low latitudes are needed to validate both satellite data and model results. Although HIAPER Pole-to-Pole Observations (HIPPO) data (Wofsy et al, 2011) are not suitable for a comprehensive validation study as in this study due to their limited observation periods, HIPPO CO 2 data are useful to validate CO 2 vertical profiles observed by satellite-borne sensors and simulated in models (Kulawik et al, 2013). In addition, there may also be large biases in retrieved CO 2 data in local source and sink regions, where model data are more Figure 11.…”

“…This spatial resolution is not sufficient for measuring individual strong local point sources of CO 2 , and therefore they have been used to estimate surface CO 2 fluxes Saeki et al, 2013a;Chevallier et al, 2014;Basu et al, 2013Basu et al, , 2014Takagi et al, 2014). CO 2 concentrations in the free troposphere can be obtained by satelliteborne sensors with thermal infrared (TIR) bands at around 4.6, 10, and/or 15 µm, provided by the following sensors: the High-Resolution Infrared Sounder (HIRS; Chédin et al, 2002Chédin et al, , 2003Chédin et al, , 2005, the Interferometric Monitor for Greenhouse Gases (IMG; Ota and Imasu, 2016), the Atmospheric Infrared Sounder (AIRS; Crevoisier et al, 2004;Chahine et al, 2005;Maddy et al, 2008;Strow and Hannon, 2008), the Tropospheric Emission Spectrometer (TES; Kulawik et al, 2010Kulawik et al, , 2013, the Infrared Atmospheric Sounding Interferometer (IASI; Crevoisier et al, 2009), and the TANSO-FTS (Saitoh et al, 2009(Saitoh et al, , 2016. Furthermore, CO 2 concentrations in several atmospheric layers within the free troposphere can be retrieved separately from high-resolution TIR spectra (Saitoh et al, 2009;Kulawik et al, 2013).…”

Algorithm update of the GOSAT/TANSO-FTS thermal infrared CO<sub>2</sub> product (version 1) and validation of the UTLS CO<sub>2</sub> data using CONTRAIL measurements

“…The Atmospheric Infrared Sounder (AIRS) has achieved more accurate observations of middle-and upper-tropospheric CO 2 concentrations (Crevoisier et al, 2004;Chahine et al, 2005;Maddy et al, 2008;Strow and Hannon, 2008). The Tropospheric Emission Spectrometer (TES) has observed CO 2 concentrations in several vertical layers with high accuracy by taking advantage of its high wavelength resolution (Kulawik et al, 2010(Kulawik et al, , 2013. The Infrared Atmospheric Sounding Interferometer (IASI) has observed upper-atmospheric CO 2 amounts from its TIR spectra (Crevoisier et al, 2009).…”

Gradients of column CO<sub>2</sub> across North America from the NOAA Global Greenhouse Gas Reference Network

“…The uncertainty of TCCON total column CO 2 is reported to be 0.4 ppm (1σ ) after comparison to aircraft measurements (Wunch et al, 2010). Vertical profiles are also used to evaluate other satellite retrievals of total column XCO 2 , such as those from the Tropospheric Emission Spectrometer (TES) (Kulawik et al, 2013) and the Greenhouse Gases Observing SATellite (GOSAT) Saitoh et al, 2016). Satellite retrieval products have known and unknown biases (due to errors in spectroscopy, viewing geometry, spatial differences in clouds and aerosols, surface albedo, etc.)…”