Is it possible to call CRTM's RT solution?

CRTM
1

Dear CRTM：
Hi. Thank you for reading this question.
I calculated the layered optical thicknesses of atmospheric gases without CRTM. is it possible to use these optical thicknesses directly as input to ADA for radiance calculations?
thanks a lot，any reply is appreciated.
Jun Shi
04/18/2023

2

Hi Jun,

Yes, this should be possible. Do you have any clouds / aerosols, or is it just clear sky values?

-Ben

3

Hi Ben,
Thank you for your reply.
My requirements are as follows: I want to establish a lookup table for retrieving the infrared optical thickness of dust aerosol. I calculate the layer OD of a large number of atmospheric profiles with LBL. Meanwhile, I also constructed aerosol profiles with different heights and ODs. However, when I tried to use cdisort for calculation, the efficiency was very slow. I wanted to use faster radiation transmission to solve this problem, so I wanted to use ADA algorithm. Since you said it can be called, can you tell me how to call it? My intention is very different from the CRTM way of calculating, because I don’t seem to need any coefficient files associated with the instrument, which means I just want to call ADA.
Thanks again
Jun Shi

4

Hi @sjj199405 ,

If you are only interested in the layer optical thickness you can obtain it in the following way:

  1. You still need to call the full forward model:
    Error_Status = CRTM_Forward( Atmosphere(ii:ii), &
                                 Sfc(ii:ii)        , &
                                 Geometry(ii:ii)   , &
                                 ChannelInfo, &
                                 RTSolution(:,ii:ii) )
  1. Afterwards you can retrieve the layer transmittance like so:
RTSolution(1,ii)%Layer_Optical_Depth(1:N_LAYERS)

and the optical depth like so:

EXP(-1.0_8*RTSolution(1,ii)%Layer_Optical_Depth(1:N_LAYERS))

The CRTM also provides an AOD model to compute AOD separately:

err_stat = CRTM_AOD( atm
                     chInfo
                     rts
                       Options=opt  ) ! Optional input