Dear Simon,

how will you manage communication? I’m asking because there is a related issue in computing absorption. It is easy to define a common interface with respect to what the functions have to provide. But in that case (and perhaps also in your case) a problem is that they require quite different input, in addition to the atmosphere. (In the case of absorption for example spectral line data for LBL functions, or a table with measured cross-section data for other functions.)

Best wishes,


On 31 Jan 2021, at 10:53, Simon Pfreundschuh wrote:

Dear Stefan,

If there's no user-configurable parameters required for molecular scattering then

using it in a control file would be trivial:


The iy method would then just need to check if the sun is on and calculate

the bulk scattering properties for the first order scattering. In this way particles

and molecules would be handle in a consistent way.

What is required for this to work is of course a class that implements the interface

defined by the ScatteringSpeciesImpl class (as indicated in the PDF).

I also would really like to highlight the following, which you seem to have

The interface that I described makes no assumptions whatsoever on the scattering

species being either particles or a gas. It essentially already implements what

you described but is even less restrictive. It only requires that a scattering species

is able to provide bulk scattering data from an atmospheric state following the

protocol defined by the ScatteringSpeciesImpl class.

I am quite sure that with this system molecular and particle scattering can be handled consistently and the need for a molecular_scattering flag. However, I also agree that it would probably be inappropriate to require Jon to use this system considering that he's just a Master's student and that this is still under

Kind regards,


From: <> on behalf of Stefan Buehler <>
Sent: Friday, January 29, 2021 8:42:21 AM
To: Simon Pfreundschuh
Cc: ARTS Developers List
Subject: Re: Simon plans for scattering properties

Hej Simon,

can you help me understand it then, please? I do want to find the best
solution, not necessarily the quickest. (But simplicity is part of the
criteria for “best”.)


On 29 Jan 2021, at 7:11, Simon Pfreundschuh wrote:

Dear Stefan,

I guess all I can say is that I am quite confident that you didn't

understand my proposal, which could quite easily handle the pressure

dependency. Anyhow, it's quite clear that you are searching for a

solution and I won't be able to provide that. So let's just cut this


From: Stefan Buehler <>
Sent: Thursday, January 28, 2021 5:02:28 PM
To: Simon Pfreundschuh
Cc: ARTS Developers List
Subject: Re: Simon plans for scattering properties

Dear Simon,

thanks for the summary!

I think I understand more or less how this works now. A bit
that so much information has to be moved around at the controlfile
level. (The copying of grids from one variable to the other, the
of the scattering data themselves.) Is the idea that you would then in
practise store and load directly the ScatteringHabits, in order to
this easier?

On where the Rayleigh scattering fits in: Patrick suggested when we
talked yesterday that perhaps a more logical way to think about this
to distinguish between *gases* and *particles*, rather than between
*absorption* and *scattering*. (Including Rayleigh scattering with the
PND system really does not work, as it turns out, as it depends on

Perhaps we should move towards a *gas* / *particle* division in ARTS.
That would mean including the Liebe rain absorption in the particle
part. It would also affect your nomenclature, since one should then
preferably talk about *ParticleSpecies* rather than
(And *gas_species* instead of *absorption_species*.)

All the best,


On 26 Jan 2021, at 22:10, Simon Pfreundschuh wrote:

Dear Stefan,

I attach the description of the new scattering system that you

I tried to keep it general to avoid getting lost in technicalities.
you have

more specific questions please let me know.

Kind regards,


<> on behalf of Stefan
Buehler <>
Sent: Monday, January 25, 2021 9:36:33 AM
To: ARTS Developers List
Subject: Simon plans for scattering properties

Dear all,

one thing I took home from the developer meeting on Friday is that I
would like to better understand Simon’s plans for the scattering
properties. We need this to make a good decision on how to proceed
the Rayleigh scattering (incorporate it into the existing scattering
data framework, or make a special case for this analytical scattering
matrix). Simon, can you please summarize your concept briefly?

All the best,


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