FOCAL-OCO2 Fast atmOspheric traCe gAs retrievaL for OCO2
M. Reuter, M. Buchwitz, O. Schneising, et al.
Institute of Environmental Physics, University of Bremen


The fast atmospheric trace gas retrieval for OCO2 (FOCAL-OCO2) has been setup to retrieve XCO2 (the column-average dry-air mole fraction of atmospheric CO2) by analyzing hyper spectral solar backscattered radiance measurements of NASA's OCO2 satellite. FOCAL includes a radiative transfer model which has been developed to approximate light scattering effects by multiple scattering at an optically thin scattering layer. This reduces the computational costs by several orders of magnitude. FOCAL's radiative transfer model is utilized to simulate the radiance in all three OCO-2 spectral bands allowing the simultaneous retrieval of CO2, H2O, and solar induced chlorophyll fluorescence.


Dr. Maximilian Reuter

Institute of Environmental Physics (IUP)
University of Bremen, FB1
Otto-Hahn-Allee 1
D-28334 Bremen

Phone: +49 (421) 218 62085
FAX: +49 (421) 218 4555
E-Mail: maximilian.reuter at

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Data Quality and Known Limitations

FOCAL's accuracy and precision has been determined by comparison with collocated ground based TCCON (Total Column Carbon Observing Network) FTS (Fourier transform spectrometer) measurements. Regional-scale (station-to-station) biases amount to about 0.6ppm. The single measurement precision (standard deviation of the difference to TCCON) is about 1.5ppm.

Mainly due to overly conservative cloud filtering using MODIS MYD35 cloud mask data, probably too few soundings are processed.

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Data Access

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The data set consists of global data covering the years 2015 and 2016.

The data-format is NCDF, one file per day, and organized as ESA's GHG CCI CRDP#4 data format.
All NCDF files are compressed into a single tar.gz file.

For more information on the data format, please read the Product Specification Document Version 3 (PSDv3) of ESA's GHG CCI project.

Condition of Use

When using FOCAL data, you agree ...

... to inform us prior to any publication where FOCAL data products are planned to be used.

... to offer us co-authorship for any planned peer-reviewed publication based on FOCAL data products. (For non peer-reviewed publications it is sufficient if you add an appropriate acknowledgement.)

... not to distribute the FOCAL data products to any third party. The only exception being colleagues working in your institute (in this case you agree to inform them about the conditions listed here and that they also have to accept these conditions).


FOCAL is in part funded by the European Union (Copernicus Climate Change Service, VERIFY project, CHE project), ESA/ESRIN (GHG-CCI II project), and the State and the University of Bremen. ECMWF provided the used meteorological profiles. The OCO-2 data were produced by the OCO-2 project at the Jet Propulsion Laboratory, California Institute of Technology, and obtained from the OCO-2 data archive maintained at the NASA Goddard Earth Science Data and Information Services Center. Additionally, NASA provided the MODIS L2 collection 6 MYD35 cloud mask data, the OMI L3 OMAERUVd v003 UV aerosol index data, and the absorption cross section database ABSCO. The used solar spectra were made available by R. L.Kurucz and G.C. Toon. The used chlorophyll fluorescence spectrum has been published by U.Rascher. TCCON data were obtained from the TCCON Data Archive, hosted by the Carbon Dioxide Information Analysis Center (CDIAC).