TIR Spectral Radiance Calibration of the GOSAT Satellite Borne TANSO-FTS With the Aircraft-Based S-HIS and the Ground-Based S-AERI at the Railroad Valley Desert Playa

Algorithm update of the GOSAT/TANSO-FTS thermal infrared CO<sub>2</sub> product (version 1) and validation of the UTLS CO<sub>2</sub> data using CONTRAIL measurements

“…Another possible factor that worsened CO 2 retrieval results is the uncertainty in the calibration of TIR V161.160 L1B spectra. As reported in Kataoka et al (2014), TANSO-FTS TIR V130.130 L1B radiance spectra had a wavelength-dependent bias ranging from 0.1 to 2 K. Although the characteristics of the spectral bias in V161.160 L1B data used in TIR V1 L2 CO 2 retrievals are still under investigation, we assumed the same degree of bias in V161.160 L1B spectra and evaluated the effect of the L1B spectral bias on the TIR CO 2 retrieval using the following …”

“…Here, G CO 2 is a gain matrix for CO 2 retrieval, d spec is a spectral bias vector based on the evaluation by Kataoka et al (2014), and d CO 2 is a vector of bias errors in retrieved CO 2 concentrations attributable to the spectral bias. The result showed that a wavelength-dependent bias comparable to V130.130 L1B spectra could yield up to 0.3 and 0.5 % uncertainties in retrieved CO 2 concentration in the UTLS regions at the northern middle latitude in spring and at the northern low latitude in summer, respectively.…”

“…The following modifications were made to the algorithm from V150.151 to V161.160: improving the TIR radiometric calibration through the improvement of calibration parameters, turning off the sampling interval non-uniformity correction, modifying the spike noise criteria of the quality flag, and reevaluating the misalignment between the GOSAT satellite and TANSO-FTS sensor. Kataoka et al (2014) reported that the biases of TANSO-FTS TIR V130.130 L1B radiance spectra based on comparisons with the Scanning High-resolution Interferometer Sounder (S-HIS) spectra for warm scenes were 0.5 K at 800-900 and 700-750 cm −1 , 0.1 K at 980-1080 cm −1 , and more than 2 K at 650-700 cm −1 . Although the magnitude of the spectral bias evaluated on the basis of V130.130 L1B data would change in V161.160 L1B data, the issue of L1B spectral bias still remains.…”

“…In the TIR V1 L2 algorithm, we estimated surface temperature and surface emissivity to correct the spectral bias inherent in the TANSO-FTS TIR L1B spectra (Kataoka et al, 2014). The existence of a relatively large spectral bias around the CO 2 15 µm absorption band in TANSO-FTS TIR L1B spectra (Kataoka et al, 2014) resulted in a decrease in the number of normally retrieved CO 2 profiles.…”

“…The existence of a relatively large spectral bias around the CO 2 15 µm absorption band in TANSO-FTS TIR L1B spectra (Kataoka et al, 2014) resulted in a decrease in the number of normally retrieved CO 2 profiles. This is probably because the TIR L1B spectral bias in the CO 2 15 µm absorption band was sometimes too large for the L2 retrieval calculation to converse in a limited iteration.…”