Abstract
The alternate mapping correlated k-distribution (AMCKD) method is studied and applied to satellite simulations. To evaluate the accuracy of AMCKD, the simulated brightness temperatures at the top of the atmosphere are compared with line-by-line radiative transfer model (LBLRTM) or the observed data which are from Advanced Himawari Imager (AHI) on board the Himawari-8, as well as Medium Resolution Spectral Imager (MERSI) on board the Fengyun-3D. The result of AMCKD is also compared with the algorithm of Radiative Transfer for the Television Observation Satellite Operational Vertical Sounder (RTTOV). Under the standard atmospheric profiles, the absolute errors of AMCKD in all longwave channels of AHI and MERSI are bounded by 0.44K compared to the benchmark results of LBLRTM, which are more accurate than those of RTTOV. In the most cases, the error of AMCKD is smaller than the NEDT at ST, while the error of RTTOV is larger than the instrument noise equivalent temperature (NEDT) at scene temperature (ST). Under real atmospheric profile conditions, the errors of AMCKD increase, because the input data from ERA-Interim reanalysis dataause bias in the satellite remote sensing results. In the most considered cases, the accuracy of AMCKD is higher than RTTOV, while the efficiency of AMCKD is slightly slower than RTTOV.
Highlights
The computational speed of radiative transfer for satellite and ground based remote sensing measurementsis always a big issue [1,2,3,4]
Alternate mapping correlated k-distribution (AMCKD) is an extended correlated k-distribution (CKD) method that is beneficial for handling gaseous overlap
AMCKD method has been extended to the application of the forward radiative transfer model for remote sensing, and the results are compared to line-by-line radiative transfer model (LBLRTM)
Summary
The computational speed of radiative transfer for satellite and ground based remote sensing measurementsis always a big issue [1,2,3,4]. Gaseous transmission in the CKD model is integrated over a smooth and monotonically increasing absorption coefficient space instead of over a tortuously variable frequency space. The CKD method requires many fewer points to calculate the spectral transmissivity than the LBLRTM, with an increase of computational efficiency by two to three orders of magnitude. The traditional CKD method maps single gas within the whole band spectral region and the same mapping is applied to the other gases, leading to a highly accurate result in the mapped gaseous absorption but relatively low accuracy to the other non-mapped gases. Alternate mapping correlated k-distribution (AMCKD) proposed in [9] is an efficient and precise CKD method, which takes the importance of all gases within the entire band into consideration. AMCKD has been successfully applied in climate models and achieved very accurate results in climate simulation [10,11]
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