Full-physics carbon dioxide retrievals from the Orbiting Carbon Observatory-2 (OCO-2) satellite by only using the 2.06 µm band

Lianghai Wu,Haili Hu,Joost Aan De Brugh,Jochen Landgraf,Otto Hasekamp,Ilse Aben,Andre Butz

doi:10.5194/amt-12-6049-2019

Abstract

Abstract. Passive remote sensing of atmospheric carbon dioxide uses spectroscopic measurements of sunlight backscattered by the Earth's surface and atmosphere. The current state-of-the-art retrieval methods use three different spectral bands, the oxygen A band at 0.76 µm and the weak and strong CO2 absorption bands at 1.61 and 2.06 µm, respectively, to infer information on light scattering and the carbon dioxide column-averaged dry-air mole fraction XCO2. In this study, we propose a one-band XCO2 retrieval technique which uses only the 2.06 µm band measurements from the Orbiting Carbon Observatory-2 (OCO-2) satellite. We examine the data quality by comparing the OCO-2 XCO2 with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON). Over land and ocean the OCO-2 one-band retrieval shows differences from TCCON observations with a standard deviation of ∼1.30 ppm and a station-to-station variability of ∼0.50 ppm. Moreover, we compare one-band and three-band retrievals over Europe, the Middle East, and Africa and see high correlation between the two retrievals with a SD of 0.93 ppm. Compared to the three-band retrievals, XCO2 retrievals using only the 2.06 µm band have similar retrieval accuracy, precision, and data yield.

Highlights

Over the past decade, space-based measurements of atmospheric carbon dioxide (CO2) have been used, along with ground-based measurements, to characterize CO2 sources and sinks in order to better understand the carbon cycle
We examine whether this claim holds for real Orbiting Carbon Observatory-2 (OCO-2) measurements by comparing the XCO2 products for both methods in terms of accuracy and data yield
A oneband retrieval using only the 2.06 μm band is only possible if surface pressure information from meteorological reanalysis/forecast is used in the retrieval algorithm

Summary

Introduction

Space-based measurements of atmospheric carbon dioxide (CO2) have been used, along with ground-based measurements, to characterize CO2 sources and sinks in order to better understand the carbon cycle. The currently operational CO2 satellites, i.e., the Greenhouse Gases Observing Satellite (GOSAT; Kuze et al, 2009) and the Orbiting Carbon Observatory-2 (OCO-2; Crisp et al, 2017), and the corresponding retrieval algorithms (e.g., Butz et al, 2009; Boesch et al, 2011; O’Dell et al, 2012; Buchwitz et al, 2017) apply a three-band approach using three spectral bands around 0.76 (O2 A band), 1.61 (weak CO2 band), and 2.06 μm (strong CO2 band) to simultaneously retrieve XCO2 and other relevant parameters such as surface albedos and aerosol properties. Prior information on the carbon dioxide profile is extracted from the CarbonTracker model for the year 2013 with an added annual increase of 2.25 ppm (Peters et al, 2007)

Retrieval algorithm and methodology

Estimated from measured radiance

Performance evaluation

Findings

Conclusions