Validate the channel transmittance of LBLRTM and RTTOV

[jianjun shi]

Dear RTTOV:
Hi
I tried to compare the AHI infrared channel transmittance calculated by LBLRTM and RTTOV.

I compared it with different approximate models, such as the channel transmittance calculated by MODTRAN and LibRadtran (Convolve with the spectral response function). The results of these models indeed show little difference from RTTOV. However, when I used LBL, the average channel transmittance calculated from LBL differed significantly from the mentioned above, especially in the absorption channels (7.2, 8.5, 13um).

I suspect there might be some issues with my LBL script. In fact, I first calculate the optical thickness of each layer use LBL, and then use the exponential function to convert the optical thickness into transmittance, then convolve.

Could you please provide a script for solving channel transmittance using LBL? I actually just want to replicate the content of this page https://nwp-saf.eumetsat.int/site/software/rttov/download/coefficients/comparison-with-lbl-simulations/.

thanks

jun shi

[James Hocking]

Hi Jun Shi,

Sorry for the delay in replying due to the Easter holiday break.

Would you be able to provide the TAPE5 you are using in your LBLRTM simulations? It might be easiest if you open a ticket on the help desk:
https://nwp-saf.eumetsat.int/site/help-desk/

Best wishes,
James

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