Abstract
This paper presents the comparison of two CO2 datasets from the National Institute for Environmental Studies (NIES) of Japan and the Atmospheric CO2 Observations from Space (ACOS) of NASA for three years (2010 to 2012). Both CO2 datasets are retrieved from the Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared spectra over High gain surface land. In this three-year period, the yield of the NIES CO2 column averaged dry air mole fractions (XCO2) is about 71% of ACOS retrievals. The overall bias is 0.21 ± 1.85 ppm and −0.69 ± 2.13 ppm for ACOS and NIES XCO2, respectively, when compared with ground-based Fourier Transform Spectrometer (FTS) observations from twelve Total Carbon Column Observing Network (TCCON) sites. The differences in XCO2 three-year means and seasonal means are within about 1 to 2 ppm. Strong consistency is obtained for the ACOS and NIES XCO2 monthly averages time series over different regions, with the greatest mean difference of ACOS to NIES monthly means over China (1.43 ± 0.60 ppm) and the least over Brazil (−0.03 ± 0.64 ppm). The intercomparison between the two XCO2 datasets indicates that the ACOS XCO2 is globally higher than NIES by about 1 ppm and has smaller bias and better consistency than NIES data.
Highlights
Atmospheric carbon dioxide (CO2 ) is the most important greenhouse gas
National Institute for Environmental Studies (NIES) gases Observing SATellite (GOSAT) Short-Wavelength InfraRed (SWIR) Level 2 v02.xx XCO2 product and Atmospheric CO2 Observations from Space (ACOS) GOSAT Level 2 v3.5 XCO2 retrievals are collected for the entire study period
High/Medium gain and land/ocean differences, the comparisons between NIES and ACOS XCO2 are limited to High gain land surface in this work
Summary
Atmospheric carbon dioxide (CO2 ) is the most important greenhouse gas. The column averaged dry air mole fractions of atmospheric CO2 (XCO2 ) has increased dramatically from 280 parts per million (ppm) in the pre-industrial era to 396 ppm in 2013 [1], most probably due to human activities, such as fossil fuel combusting, land use change, cement production and biomass burning. Ground-based observations of greenhouse gas can provide accurate and high–frequent CO2 measurements Their sparse and uneven global distributions lead to large uncertainties in the estimates of CO2 amount and flux on sub-continental or regional spatial scales [3,4,5]. The preliminary validation of ACOS Level 2 v3.3 XCO2 against TCCON data showed that the mean bias and standard deviation were 1.34 and 1.83 ppm [19]. Kulawik et al [22] validated the precision characteristics, season cycle, yearly growth and daily variability of ACOS v3.5 XCO2 based on TCCON data. These XCO2 products were validated or compared with ground-based FTS data or model simulations.
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