XCO<sub>2</sub> retrieval for GOSAT and GOSAT-2 based on the FOCAL algorithm
<p>Since 2009, the Greenhouse gases Observing SATellite (GOSAT) has performed radiance measurements in the near-infrared (NIR) and shortwave infrared (SWIR) spectral region. From February 2019 onward, data from GOSAT-2 have also been available.</p> <p>We present the first resu...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-05-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/14/3837/2021/amt-14-3837-2021.pdf |
| Summary: | <p>Since 2009, the Greenhouse gases Observing SATellite (GOSAT) has performed
radiance measurements in the near-infrared (NIR) and
shortwave infrared (SWIR) spectral region.
From February 2019 onward, data from GOSAT-2 have also been available.</p>
<p>We present the first results from the application of the Fast atmOspheric
traCe gAs retrievaL (FOCAL) algorithm to derive
column-averaged dry-air mole fractions of carbon dioxide (<span class="inline-formula">XCO<sub>2</sub></span>) from GOSAT and
GOSAT-2 radiances and their validation.
FOCAL was initially developed for OCO-2 <span class="inline-formula">XCO<sub>2</sub></span> retrievals and
allows simultaneous retrievals of several gases over both land and
ocean.
Because FOCAL is accurate and numerically very fast, it is currently
being considered as a candidate algorithm for the forthcoming European
anthropogenic <span class="inline-formula">CO<sub>2</sub></span> Monitoring (CO2M) mission to be launched
in 2025.</p>
<p>We present the adaptation of FOCAL to GOSAT and discuss the changes
made and GOSAT specific additions.
This particularly includes modifications in pre-processing (e.g. cloud
detection) and post-processing (bias correction and filtering).</p>
<p><span id="page3838"/>A feature of the new application of FOCAL to GOSAT and GOSAT-2 is the
independent use of both S- and P-polarisation spectra in the retrieval.
This is not possible for OCO-2, which measures only one polarisation
direction.
Additionally, we make use of GOSAT's wider spectral coverage compared
to OCO-2 and derive not only <span class="inline-formula">XCO<sub>2</sub></span>, water vapour
(<span class="inline-formula">H<sub>2</sub>O</span>), and solar-induced fluorescence (SIF) but also methane
(<span class="inline-formula">XCH<sub>4</sub>)</span>, with the potential for further atmospheric
constituents and parameters like semi-heavy water vapour (<span class="inline-formula">HDO</span>). In the case of GOSAT-2, the retrieval of nitrous oxide (<span class="inline-formula">XN<sub>2</sub>O</span>) and carbon monoxide (<span class="inline-formula">CO</span>) may also be possible.</p>
<p>Here, we concentrate on the new FOCAL <span class="inline-formula">XCO<sub>2</sub></span> data products.
We describe the generation of the products as well as applied
filtering and bias correction procedures.
GOSAT-FOCAL <span class="inline-formula">XCO<sub>2</sub></span> data have been produced for the time interval 2009 to 2019. Comparisons with other independent GOSAT data sets reveal
agreement of long-term temporal variations within about
1 <span class="inline-formula">ppm</span> over 1 decade; differences in seasonal variations of
about 0.5 <span class="inline-formula">ppm</span> are observed.
Furthermore, we obtain a station-to-station bias of the new GOSAT-FOCAL
product to the ground-based Total Carbon Column Observing Network
(TCCON) of 0.56 <span class="inline-formula">ppm</span> with a mean scatter of 1.89 <span class="inline-formula">ppm</span>.</p>
<p>The GOSAT-2-FOCAL <span class="inline-formula">XCO<sub>2</sub></span> product is generated in a similar way as the
GOSAT-FOCAL product, but with adapted settings. All GOSAT-2 data until the end of 2019 have been processed. Because of this limited time interval, the GOSAT-2 results are considered to be preliminary only, but first comparisons show that these data compare well with the GOSAT-FOCAL results and also TCCON.</p> |
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| ISSN: | 1867-1381 1867-8548 |