Improved retrieval of gas abundances from near-infrared solar FTIR spectra measured at the Karlsruhe TCCON station
We present a modified retrieval strategy for solar absorption spectra recorded by the Karlsruhe Fourier Transform Infrared (FTIR) spectrometer, which is operational within the Total Carbon Column Observing Network (TCCON). In typical TCCON stations, the 3800–11 000 cm<sup>&minu...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-02-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/9/669/2016/amt-9-669-2016.pdf |
| Summary: | We present a modified retrieval strategy for solar absorption spectra recorded
by the Karlsruhe Fourier Transform Infrared (FTIR) spectrometer, which is
operational within the Total Carbon Column Observing Network (TCCON). In
typical TCCON stations, the 3800–11 000 cm<sup>−1</sup> spectral
region is measured on a single extended Indium Gallium Arsenide (InGaAs)
detector. The Karlsruhe setup instead splits the spectrum across an Indium
Antimonide (InSb) and InGaAs detector through the use of
a dichroic beam splitter. This permits measurements further into the mid-infrared (MIR)
that are of scientific interest, but are not considered TCCON
measurements. This optical setup induces, however, larger variations in the
continuum level of the solar spectra than the typical TCCON setup. Here we
investigate the appropriate treatment of continuum-level variations in the
retrieval strategy using the spectra recorded in Karlsruhe. The broad spectral
windows used by TCCON require special attention with respect to residual
curvature in the spectral fits.
To accommodate the unique setup of Karlsruhe, higher-order discrete Legendre
polynomial basis functions have been enabled in the TCCON retrieval code to fit
the continuum. This improves spectral fits and air-mass dependencies for
affected spectral windows. After fitting the continuum curvature, the
Karlsruhe greenhouse gas records are in good agreement with other European
TCCON data sets. |
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| ISSN: | 1867-1381 1867-8548 |