On 27/06/18 15:40, Roberto Marzocchi wrote:
Il giorno mer 27 giu 2018 alle ore 15:25 Markus Metz
<[email protected] <mailto:[email protected]>>
ha scritto:
On Wed, Jun 27, 2018 at 3:06 PM, Roberta Fagandini
<[email protected] <mailto:[email protected]>> wrote:
>
>
>
> 2018-06-27 14:24 GMT+02:00 Markus Metz
<[email protected] <mailto:[email protected]>>:
>>
>>
>>
>> On Wed, Jun 27, 2018 at 2:16 PM, Roberta Fagandini
<[email protected] <mailto:[email protected]>> wrote:
>> >
>> > I'm trying to create an automatic procedure to retrieve all
the input parameters for the control file of i.atcorr.
>> > I need py6S because I want to automatically read and compute
AOT at 550nm from an AERONET file.
>>
>> With AOT you mean aerosol optical thickness right? This is user
input to i.atcorr. There are various sources for AOT at 550nm, e.g.
MODIS.
>
>
> Right!
>
>>
>>
>>
>>
>> Anyway, it is probably much easier to to write your own routine
to read the AERONET file and get the corresponding formula for AOT
than to fight with 51821 lines of Fortran source code that is
numerically unstable. Maybe I can help with getting AOT at 550nm
from an AERONET file avoiding the Fortran version of 6S.
>
>
> Ok but I'm not able to create this kind of routine on my own. If
someone, more expert than me, can help me in translating the 6S/Py6S
functions I can go on in this way otherwise for me it's easier to
use the fortran source code.
Apparently the AERONET data are simple CSV files. You can import
them with r.in.xyz <http://r.in.xyz> or v.in.ascii.
Still, I think it is up to the user to decide on the source of AOT
values. AERONET is one of many possible sources.
Ok but I know that Roberta want try to simplify the procedure for
atmospheric correction. In particular she would like to add an option
(not the only one) to read automatically the AOT at the wave length of
550 nm from the AERONET file.
The steps to do this IMHO are:
1) read the file (using GRASS or maybe better Python)
2) a formula to calculate the AOT550
Unfortunately I have no idea about the 2nd point :-(
I'm not sure either, what exactly the necessary calculations are.
Superficially reading through the relevant class in Py6S [1], I
understasnd that it does two things:
1) Get the value of AOT550
2) Create a continuous profile by interpolating values
If all you need is 1), then all they do (see _get_aot() method at the
end) is to read all the AOT_* columns and chose the value of the line
with the timestamp closest to the one asked for and the wavelength
closest to 550.
As the code is GPL you could probably just extract the necessary parts
and integrate them into your code. The only thing I'm not to sure about
is their use of pandas which creates yet again another dependency which
I don't really think necessary and desirable.
It should be enough to extract from the file the date and time (or maybe
easier to work with: year and the Julian day) and all AOT_* columns,
parse the AOT_* columns for their wavelength value and then identify the
value which has closes time and wavelength to the time requested and 550nm.
Moritz
[1] https://github.com/robintw/Py6S/blob/master/Py6S/SixSHelpers/aeronet.py
_______________________________________________
grass-dev mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/grass-dev
