On 28/01/22 10:55, ilaria.ferrand...@gmail.com wrote:
Thank you Moritz, I will do some research on visibility (aerosol model
concentration) to put a reasonable value there (any suggestion is appreciated,
also regarding references to look at).
The man page suggests https://aeronet.gsfc.nasa.gov/.
How can I transform digital number into radiance/reflectance?
This information should be in the metadata that accompanies the Sentinel
data. I haven't worked with this data in a couple of years, so don't
remember.
However, in the doc on
https://docs.sentinel-hub.com/api/latest/data/sentinel-2-l2a/, you can read:
For Sentinel-2 optical data, the relation between DN and REFLECTANCE
(default unit) is: DN = 10000 * REFLECTANCE.
Moritz
Thank you very much for your precious help!
-----Messaggio originale-----
Da: Moritz Lennert <mlenn...@club.worldonline.be>
Inviato: giovedì 27 gennaio 2022 17:50
A: ilaria.ferrand...@gmail.com; 'Maris Nartiss' <maris....@gmail.com>
Cc: 'GRASS user list' <grass-user@lists.osgeo.org>
Oggetto: Re: R: R: [GRASS-user] NULL values as output of i.atcorr
On 27/01/22 14:54, ilaria.ferrand...@gmail.com wrote:
The output of r.info is the following
r.info map=immagine@mapset
+----------------------------------------------------------------------------+
| Map: immagine@mapset Date: Tue Nov 30 12:51:12 2021 |
| Mapset: mapset Login of Creator: [...] |
| Location: WGS84_UTM32
|
| DataBase: C:\Users\[...]\grassdata |
| Title: immagine
|
| Timestamp: none
|
|----------------------------------------------------------------------------|
|
|
| Type of Map: raster Number of Categories: 0
|
| Data Type: CELL
|
| Rows: 10980
|
| Columns: 10980
|
| Total Cells: 120560400
|
| Projection: UTM (zone 32)
|
| N: 4900020 S: 4790220 Res: 10
|
| E: 609780 W: 499980 Res: 10
|
| Range of data: min = 0 max = 18876
|
|
|
| Data Description:
|
| generato da r.in.gdal
|
|
|
| Comments:
|
| r.in.gdal -e input="C:\Users\[...]\T32TNP_2020062\ |
| 2T100559_B04.jp2" output="immagine" memory=300 offset=0 num_digits=0
|
|
|
+---------------------------------------------------------------------
-------+
This looks to me like the data is in digital number, not in radiance or
reflectance. You first have to translate it to one or the other before feeding
it to i.attcor.
Do you mean the sixth line of the file? From the i.atcorr help it is the "mean
target elevation above sea level [km]", and it is correct that it is negative.
I'm now wondering if the problem can be having put "0" for visibility (aerosol
model concentration, fifth line). What do you think about it?
I am speaking about the value '-0.293' in line 6 (and yes, my bad for not
paying attention to the value 0 in the line before). The man page
states: "If you have an estimate of aerosol optical depth, enter 0 for the
visibility and in a following line enter the aerosol optical depth at 550nm (iaer means
'i' for input and 'aer' for aerosol), for example:"
So, if you have 0 on line 5, so line 6 is AOD and not mean target elevation
above sea level.
In this case line 7 is the "mean target elevation above sea level [-km]"
with value -1000 :-).
Moritz
-----Messaggio originale-----
Da: Moritz Lennert <mlenn...@club.worldonline.be>
Inviato: giovedì 27 gennaio 2022 14:08
A: ilaria.ferrand...@gmail.com; 'Maris Nartiss' <maris....@gmail.com>
Cc: 'GRASS user list' <grass-user@lists.osgeo.org>
Oggetto: Re: R: [GRASS-user] NULL values as output of i.atcorr
On 27/01/22 14:01, ilaria.ferrand...@gmail.com wrote:
Dear Moritz,
thank you for your reply.
I tried with and without the -r flag and the results is the same.
I reformulate this part of the question then: what exactly is the
content of immagine@mapset ? Please provide the output of
r.info map=immagine@mapset
Please find attached the parameters of the file 22giugno2020_b4.txt:
26
6 22 17.05 9.68728523 43.75514951
2
1
0
-0.293
Are you sure this should be a negative number ? This should be visibility in km
IIRC.
-1000
182
Moritz
-----Messaggio originale-----
Da: Moritz Lennert <mlenn...@club.worldonline.be>
Inviato: giovedì 27 gennaio 2022 13:22
A: Ilaria Ferrando <ilaria.ferrand...@gmail.com>; Maris Nartiss
<maris....@gmail.com>
Cc: GRASS user list <grass-user@lists.osgeo.org>
Oggetto: Re: [GRASS-user] NULL values as output of i.atcorr
On 26/01/22 19:50, Ilaria Ferrando wrote:
Dear Māris,
Thank you for your reply.
Yes, the image is inside the computational region.
Any other ideas?
1) Are you sure your input data is reflectance (-r flag used) ?
2) Could you provide us with the contents of the 22giugno2020_b4.txt file ?
Moritz
Il mer 26 gen 2022, 19:45 Maris Nartiss <maris....@gmail.com
<mailto:maris....@gmail.com>> ha scritto:
One thing to always check – does your computational region contain
data you are analysing? Try to run `g.region rast=immagine` before
running i.atcorr.
Māris.
trešd., 2022. g. 26. janv., plkst. 18:13 — lietotājs
<ilaria.ferrand...@gmail.com <mailto:ilaria.ferrand...@gmail.com>>
rakstīja:
>
> Dear all,
>
> I am having troubles in processing a Sentinel-2 image with i.atcorr.
>
> The command I use is the following:
>
> i.atcorr -r -input=immagine@mapset range=0,10000
parameters=C:\...\22giugno2020_b4.txt output=immagine_atcorr rescale=0,1
>
> and I obtain this output:
>
> wavelength less than 0.25 micron:
>
> let's take s(l)=s(0.25)
>
> Atmospheric correction...
>
> Atmospheric correction complete.
>
>
>
> The map I obtain is constituted by pixels with 6.669033e-34 values.
>
> Can anyone explain the meaning of the output and why I obtain a
NULL value corrected map?
>
> Thank you for your support.
>
>
>
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