Dear Stefan,

If you have a controlfile to compute the od and tangent altitude

it should be fairly easy to wrap this into a python function and

use scipy.optimize.root to find the zero of od - 1.0.



<> on behalf of Stefan Buehler 
Sent: Friday, March 9, 2018 3:17:42 PM
To: ARTS Development List
Subject: [arts-dev] Transit radius

Dear all,

here is an ARTS challenge, not strictly important right now, but for my own 
curiosity. Probably mostly to Patrick, but perhaps interesting also for others.

For exoplanet research, one observation technique provides the planet's transit 
radius, that is, the tangent radius where the optical depth of the limb path is 

Can we generate this with ARTS? The simple-minded way I can come up with is to 
do a limb simulation and store opacity for each pencil-beam, along with its 
tangent altitude. Then interpolate to find the tangent altitude for which the 
opacity along the limb path is one.

Is there a smarter way?

And, for the way I outlined, what is the currently recommended way to get out 
tangent altitude and opacity along the los?

If it is easy to generate, I feel tempted to include a “transit radius” view to 
the nadir spectrum figure in the paper.

Best wishes,


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