Enabling solar radiation in RTTOV

[SWADHIN SATAPATHY]

Hi All,

I’m trying to add the solar contribution to the spectrum while running RTTOV. I did that by setting myRttov.Options.AddSolar = True. But as per the user guide it will only add the solar contribution to the IR channels in the 3-5 micron range. It is also mentioned that users have noted that a solar contribution due to sun glint can be detected even in window channels in the thermal IR. By default these channels are considered thermal-only, but it is possible to include the solar contribution for them by setting the element of coefs%coef%ss_val_chn(:) corresponding to the channel in question to 1 after the coefficient file has been read.

Is there a way I can do that in the python wrapper, to include the contribution due to sun glints in the thermal IR channels (10-12 micron)?

[James Hocking]

Hi,

You can’t do this in code in the wrapper, but you can achieve the same thing by editing the rtcoef file directly. Look for the “SOLAR_SPECTRUM” section. The second column contains the flag indicating thermal-only (0), solar-only (2), or mixed thermal+solar (1) for each channel. For the thermal IR channels of interest, change the 0 to 1. (As an aside it is worth saying that you must not change any solar-only channels to mixed (i.e., do not change 2 to 1) because this will not work).

Note that if the instrument is in low-Earth orbit then the thermal IR channels will only have been trained over 6 secants (up to zenith angles at around 65 degrees). Therefore the accuracy of the optical depth prediction will be degraded for larger solar zenith angles.

Best wishes,
James

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