GOSAT/GOSAT-2 EORC Daily Partial Column GHGs

GOSAT V02 GOSAT-2 V01

JAXA EORC GOSAT retrieval

Last update: 2022/01/05

1. Partial Column Density overview

GOSAT uses the multiplex advantage of the FTS technology, which enables simultaneous measurements of solar-reflected lights and thermal emissions of the Earth’s atmosphere with a single instrument. Existing GOSAT Level 2 products (e.g. NIES/GOSAT and NASA’s ACOS) have provided the column-averaged dry-air mole fractions of CO2 and CH4 (XCO2 and XCH4, respectively), but only from the three SWIR-bands. TIR spectra emitted from CO2 and CH4 contain vertical profile information, due to the temperature gradient. Conventional algorithms for the TIR band have attempted to acquire CO2 and CH4 densities for ten vertical layers in the troposphere, resulting in unstable retrievals due to the uncertainties of radiometric calibrations. In addition, TIR data alone do not contain enough information of near-surface CO2 and CH4.

The JAXA EORC GOSAT group has reduced the number of vertical layers for a more robust retrieval. They can retrieve the difference between the partial column-averaged dry-air mole fractions of the two individual layers of the lower and upper troposphere XCO2LT, XCO2UT, XCH4LT, and XCH4UT by combining TIR and SWIR spectra data simultaneously, thereby constraining the accurate total column density of XCO2 and XCH4. They retrieved five vertical layers: two in the troposphere and three in the stratosphere. They used the entire spectral range acquired with the FTS including absorption bands of O2 A at 0.76 μm, CO2 and CH4 at 1.6 μm, and CO2 at 2.0 μm, and thermal emission from atmospheric CO2 and CH4. The simultaneous use of two liner polarizations can provide accurate light-path modification under thick aerosol conditions.

The retrieval method is the maximum a posteriori solution found by minimizing a cost function. For reflected solar light, we used the vector equation of radiative transfer for the diffuse components of the Stokes parameters. We define vertical layers of LT and UT not by temperature, but by the retrieved surface pressure (Psurf) from individual O2 A band data as retrieved vertical temperature has a larger uncertainty. The pressure-height ranges of the LT and UT were taken as 0.6-1 Psurf and 0.2-0.6 Psurf, respectively. Both LT and UT have the same air masses. The exact ranges of each vertical layer were determined by individually retrieved Psurf. In the case of ocean data, the vertical range of LT becomes 0-4 km. We allocate three layers in the stratosphere to stabilize the retrieval. Most pieces of information on the stratosphere come from a priori data. The typical degrees of freedom for the signal (DFS) are roughly 1.2, 1.8, 0.6, 0.8 for XCO2, XCH4, XCO2LT, and XCH4LT, respectively. Therefore, most of the lower troposphere data are acquired from GOSAT observations. They validated our XCO2LT and XCH4LT retrieval algorithm by coincident spiral flights with an airborne spectrometer during the annual calibration and validation campaigns at Railroad Valley in Nevada, USA.

In addition to CO2 and CH4, they provide 11-layer H2O density. TANSO-FTS contains wide H2O bands and H2O have more complicated vertical profiles; therefore 11-layer data are retrieved.

2. Data description

2.1 Data Access

 Available at https://www.eorc.jaxa.jp/GOSAT/index.html

2.2 Product version

 Version 2
  Based on the version 230.231 of the Level 1B products

2.3 Data Period

 GOSAT Data period, 2009-2020 (2013-2020 as of October 17)
  Contents: Successfully retrieved single point data acquired from a single interferogram (Level 1 A) by TANSO-FTS per line

2.4 Format

 One file per month.
  Format text.

GOSAT Version 2 (230231)

  • yyyy/mm/dd and hh:mm:ss :
    Observation time defined as the start time of the exposure.
  • LSFLG :
    land/sea flag [0 ... land | 1 ... sea | 2 ... mixed]
  • XH2O_apr :
    a priori column averaged VMR of water vapor [ppmv]
  • XH2O :
    retrieved column averaged VMR of water vapor [ppmv]
  • H2O_apr_** :
    a priori VMR of water vapor in the **-th layer [ppmv]
    The VMR of water vapor is retrieved with 11 vertical layers whose interfaces are defined as
    0.1 hPa and [0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0] * Psrf_ret.
  • XH2O_** :
    retrieved VMR of water vapor in the **-th layer [ppmv]
    The VMR of water vapor is retrieved with 11 vertical layers whose interfaces are defined as
    0.1 hPa and [0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0] * Psrf_ret.
  • XGAS_apr :
    a priori column averaged VMR of GAS [ppmv]
  • XGAS :
    retrieved column averaged VMR of GAS [ppmv]
  • XGAS_apr_UT :
    a priori VMR of GAS [ppmv] in the upper troposphere
    upper troposphere (UT) ... from 0.2*Psrf_ret down to 0.6*Psrf_ret
  • XGAS_apr_LT :
    a priori VMR of GAS [ppmv] in the lower troposphere
    lower troposphere (LT) ... from 0.6*Psrf_ret down to Psrf_ret
  • XGAS_UT :
    retrieved VMR of GAS [ppmv] in the upper troposphere
    upper troposphere (UT) ... from 0.2*Psrf_ret down to 0.6*Psrf_ret
  • XGAS_LT :
    retrieved VMR of GAS [ppmv] in the lower troposphere
    lower troposphere (LT) ... from 0.6*Psrf_ret down to Psrf_ret
  • Psrf_apr :
    a priori surface pressure [hPa]
  • Psrf_ret :
    retrieved surface pressure [hPa]
  • AOT_xyz :
    retrieved AOT at wavelength xyz
  • SIF :
    SIF (constant in wavenumber) [10^-9 W/cm^2/sr/cm^-1]
  • Cloud :
    cloud cover [0.0 - 1.0]

3. Condition of use

Please do not distribute this product to any third party. If you plan to publish your research outcome using this product, please inform and consult us in advance.

4. Citation

  • Kikuchi, N., Kuze, A., Kataoka, F., Shiomi, K., Hashimoto, M., Suto, H., et al., "Three-dimensional distribution of greenhouse gas concentrations over megacities observed by GOSAT", AGU fall meeting, (2017).
  • A. Kuze et al., “Update on GOSAT TANSO-FTS performance, operations, and data products after more than 6 years in space,” Atmos. Meas. Tech., 9, 2445-2461, (2016).
  • The SWIR part of the algorithm is described by Kikuchi et al.: Kikuchi, N., Y. Yoshida, O. Uchino, J. Morino, and T. Yokota: "An advanced retrieval algorithm for greenhouse gases using polarization information measured by GOSAT TANSO-FTS SWIR I: Simulation study", J. Geophys. Res., 121, 21, 13129-13157, doi:10.1002/2015JD024720, (2016).
  • A. Kuze et al., “Level 1 algorithms for TANSO on GOSAT: Processing and on-orbit calibrations,” Atmos. Meas. Tech., 5, 2447-2467 (2012).

5. Reference

Ancillary data

6. Links

7. Acknowledgments

GHG Long term trend viewer was developed by JAXA/EORC. We would like to thank NIES GOSAT project members, and JAXA GOSAT project members.

8. Contact

Please contact shiomi.kei@jaxa.jp suto.hiroshi@jaxa.jp kuze.akihiko@jaxa.jp for the access.

9. Note

Post screening will be added to remove outliers.