Implications for Molecular Spectroscopy Inferred from IASI Satellite Spectral Measurements
| Main Authors: | Tony Clough, Mark Shephard |
|---|---|
| Format: | info Proceeding Journal |
| Terbitan: |
, 2008
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/17533 |
Daftar Isi:
- IASI (Infrared Atmospheric Sounder Interferometer) is a spatially scanning Michelson interferometeric emission spectrometer covering the spectrum from 645 to 2760 cm_1 with a resolution 0.25 cm_1 (Gaussian 1/e). The instrument has a demonstrated photometric accuracy of _0.1 K in Brightness Temperature through much of this spectral region. We present here analyses for two IASI spectra, one acquired over the Southern Great Plains ARM site, the other over the Gulf of Mexico. Modeling of the radiance spectra with a level of accuracy consistent with that of the data provides a significant challenge. The objective here is to validate and improve the forward radiative transfer model including the associated continua and line parameters for the highly inhomogeneous radiating atmosphere Validation of the atmospheric radiative transfer model is particularly challenging given the difficulty of providing an adequate specification of the radiating atmosphere and surface. For the present analysis radiosondes have been used for the initial guess followed by the retrieval of temperature, water vapor, methane, and carbon monoxide. The spatial and temporal variability of water vapor in the atmosphere essentially precludes the use of radiosondes for validation. The forward model used in these analyses is LBLRTM v11.3. The line parameters are based on HITRAN 2004 and associated updates with specific exceptions. The line parameters for carbon dioxide have been replaced by those available from Niro et al.1 including P-Q-R line coupling. The implementation uses first order perturbation theory derived from the relaxation matrices of Niro et al. The continuum is mt ckd 2.1. The inclusion of line coupling requires redefinition of the fundamental continuum function which will be discussed in some detail. No adjustment in the carbon dioxide line shape has yet been made for duration of collision effects. The overall results are remarkably good based on the analysis of the residuals. The need for a modification to the CO2 line shape is clearly evident in the 2385 cm_1 region. The consistency between the _2 and _3 bands is remarkably good. The residuals in the 1600 cm_1 water vapor region are the largest in the entire spectrum presumably primarily due to issues with the spectroscopy but atmospheric inhomogeneity may play some role. Velocity broadening has not been applied in these analyses. A validation using new water vapor line strengths due to L. Coudert will be shown for comparison.
- Session IV-1.