Thank you, Richard and Stefan,

Yes, that is the difference that I am getting at 183 GHz.

Does the scattering calculation methods in ARTS even now accept only RJBT units 
? Are Planck units going to be enabled for scattering solvers anytime soon?

From: Richard Larsson <>
Sent: Tuesday, April 20, 2021 5:42 AM
To: Thomas,Renish <>
Cc: Stefan Buehler <>; <>
Subject: Re: [arts-users] Calculated brightness temperature bias causes.


Just by numbers:

RJBT at 300 K 183 GHz is 3.086705214957283e-15

Planck at 300 K 183 GHz is 3.0417434132511342e-15

This means you expect a 1.5 % difference, or about 4.5 K between them.

With hope,

Den tis 20 apr. 2021 kl 13:22 skrev Thomas,Renish 
Hi Stephan,

I am using Rayleigh jeans. As I need to activate cloud box in some instances.

I understand that RJBT instead of Planck can cause a dip in the brightness 
temperatures. Is this the only factor that can cause a bias, or does pressure 
levels, lat/lon grid resolution also cause a bias?


-------- Original message --------
From: Stefan Buehler 
Date: 4/20/21 6:11 AM (GMT-06:00)
To: "Thomas,Renish" 
Subject: Re: [arts-users] Calculated brightness temperature bias causes.

Dear Renish,

do you use Planck or Rayleigh-Jeans brightness temperature? For Planck,
you should indeed approach the ambient temperature if you go low enough.



On 20 Apr 2021, at 12:46, Thomas,Renish wrote:

> Hi Everyone,
> I had some questions about the calculated brightness temperature in
> When I calculate the brightness temperature for an atmospheric
> scenario in "horizon looking mode" and in clearsky. I get a brightness
> temperature at 183.31 GHz (Water vapor absorption line), which is
> about 3 to 6 degrees lower than the ambient temperature.
> I would assume that at the water vapor absorption line and at low
> altitudes (~2 km above sea level), I should measure very close to the
> ambient temperature (Due to high absorption).
> So, my questions are:
> 1.)  Is this brightness temperature bias expected?, or can something
> else cause this?
> Thanks,
> Renish
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