Questions about the output of transmittance

[liu xuan]

Hi,

I’m using the RTTOV_SCATT module to calculate the weight function of the AMSR2 microwave radiometer. Here, we need to use the optical depth or transmittance of each layer. There is a parameter called emiss_retrieval_terms in the RTTOV_SCATT module. Its explanation is that the output structure contains radiation and transmission data, which can be used for all-sky emission retrievals. However, I also found another module-Transmission Struture. One of the parameters is tau_levels (nlevel, nchanprof). This can also output the transmittance of each layer. I want to know which of these two modules can obtain the transmittance of each pressure layer. Looking forward to your reply.

Thanks

[James Hocking]

Hi,

The transmission structure is not an output of RTTOV-SCATT, and the emissivity retrieval terms structure only contains total atmospheric transmittances, not level-to-space transmittances.

Unfortunately it is not possible to obtain level-to-space transmittances from RTTOV-SCATT. You can obtain clear-sky transmittances by running the same simulation in RTTOV (and if using v13.1 or v13.2 you can set opts%rt_all%transmittances_only to true for faster calculations). These are transmittances for the RTTOV pressure levels, not the RTTOV-SCATT pressure half-levels.

There is not currently any way to obtain cloudy transmittances from RTTOV-SCATT.

Best wishes,
James

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