GHGs Trend Viewer
with GOSAT Long term target observation

JAXA EORC GOSAT retrieval

Last update: 2022/09/07

1. Introduction

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.

The GHG long term trend viewer presents quick view and pick up data set of the target observation sites, where users are interested. Most of the target observations requested by the RA researchers are not included in the list.

2. Data description

L1B version

About data category

About parameter

About data extraction

In order to use long term trend data of the point of interest, the viewer pick up data within the circle of 10km radius.

But the following adjacent site, the viewer pick up within the circle of 1km or 2km radius.

[circle of 1km radius]

Osaka3, Osaka4
Bakersfield4 - 6
Boston4, Boston5, Greece4, Greece5

[circle of 2km radius]

JPL Tokyo6, 8, 11 - 13
Osaka5
Bakersfield2, Bakersfield3
Aliso_Canyon2 - 4
Namibia1 - 3
Antarctica1 - 4
Beijing1 - 16
Shanghai1 - 13
Delhi1 - 16
Dhaka1 - 16
MexicoCity1 - 16
Istanbul1 - 16
Cairo1 - 15
CebuIsland1, 2
Sacramento(Rice Field), Sacramento(CA Capitol)
Karachi1 - 16
Lahore1 - 16
East_Hokkaido1 - 14

[circle of 2.5km radius]

Caltech_USA

The primary pointing system, which had been used between launch and Dec. 2014, larger pointing offset of about 5km.

Therefore, some cases include nearby target points.

3. Citation

Algorithm:

Ancillary data

4. Links

5. 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.

6. 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.