Carbon dioxide retrieval from OCO-2 satellite observations using the RemoTeC algorithm and validation with TCCON measurements

Lianghai Wu,Thorsten Warneke,Jochen Landgraf,Dietrich G Feist,Kei Shiomi,Dmitry Koshelev,Frank Hase,Haili Hu,Ralf Sussmann,Rigel Kivi,Yao Té,Isamu Morino,Joost Aan De Brugh,Justus Notholt,Martine De Mazière,Hirofumi Ohyama,Otto Hasekamp,David F Pollard ,Tae‐Young Goo ,Mat­thias Schneider ,G C Toon ,A Butz ,I Aben ,L T Iraci ,David Griffith

doi:10.5194/amt-11-3111-2018

Abstract

Abstract. In this study we present the retrieval of the column-averaged dry air mole fraction of carbon dioxide (XCO2) from the Orbiting Carbon Observatory-2 (OCO-2) satellite observations using the RemoTeC algorithm, previously successfully applied to retrieval of greenhouse gas concentration from the Greenhouse Gases Observing Satellite (GOSAT). The XCO2 product has been validated with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON) for almost 2 years of OCO-2 data from September 2014 to July 2016. We found that fitting an additive radiometric offset in all three spectral bands of OCO-2 significantly improved the retrieval. Based on a small correlation of the XCO2 error over land with goodness of fit, we applied an a posteriori bias correction to our OCO-2 retrievals. In overpass averaged results, XCO2 retrievals have an SD of ∼ 1.30 ppm and a station-to-station variability of ∼ 0.40 ppm among collocated TCCON sites. The seasonal relative accuracy (SRA) has a value of 0.52 ppm. The validation shows relatively larger difference with TCCON over high-latitude areas and some specific regions like Japan.

Highlights

Carbon dioxide (CO2) concentration is rapidly increasing in the atmosphere due to fossil fuel combustion and deforestation (Prentice et al, 2001)
By taking advantage of the target mode where many observations are acquired over ground-based validation sites, the biases in the XCO2 retrievals from Orbiting Carbon Observatory-2 (OCO-2) measurements can be accurately evaluated
We focus on satellite observations that are collocated with measurements from the Total Carbon Column Observing Network (TCCON), which is a global network of ground-based instruments that can measure XCO2 in the atmosphere (Wunch et al, 2011a)

Summary

Introduction

Carbon dioxide (CO2) concentration is rapidly increasing in the atmosphere due to fossil fuel combustion and deforestation (Prentice et al, 2001). The thermal infrared observations of CO2 from instruments like the Atmospheric Infrared Sounder (AIRS), the Tropospheric Emission Spectrometer (TES) and the Infrared Atmospheric Sounding Interferometer (IASI) can provide CO2 measurements at altitudes between 5 and 15 km (Chédin et al, 2002; Engelen et al, 2004; Crevoisier et al, 2009). These measurements have a limited sensitivity to CO2 in the lower troposphere where CO2 sources and sinks are located. With a spatial sampling size of about 3 km, the number of cloud-free XCO2 OCO-2 observations exceeds significantly those of previous missions

Methods

Findings

Discussion

Conclusion