Cheers
Stefan
-----Original Message-----
From: grass-user [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of
Moritz Lennert
Sent: mandag 18. desember 2017 16.26
To: Žofie Cimburová <zoficimbur...@gmail.com>
Cc: GRASS user list <grass-user@lists.osgeo.org>
Subject: Re: [GRASS-user] i.atcorr with Sentinel2
On 18/12/17 16:13, Žofie Cimburová wrote:
Dear Moritz,
According to
https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/product-
types , the L1C product I am using already is in top of atmosphere
reflectance, so this should not be the problem (?).
I tried running i.atcorr both with and without the -r flag.
Reflectance is the percentage of light that is reflected either from the top of
the atmosphere or from the surface. Reflectance values should thus be real
values between 0 and 1. Your data have
Range of data: min = 1 max = 28000
This means that they are expressed in digital (integer) numbers. Try
transforming these DN into real numbers. IIRC, in the metadata, you have a
variable QUANTIFICATION_VALUE. Divide your pixel values by that value to get
real TOA reflectance values.
AFAIK, it also depends on whether you directly imported the original 12-bit
file, or possibly a modified, e.g. 16-bit, version.
Moritz
On Mon, Dec 18, 2017 at 3:35 PM, Moritz Lennert
<mlenn...@club.worldonline.be <mailto:mlenn...@club.worldonline.be>> wrote:
On 18/12/17 13:14, Žofie Cimburová wrote:
Hi all,
Now the 6S parameters are complete, but the output map contains
only NULLs, no matter what combinations of input parameters and
flags I use. Have anyone encountered the same issue? (Info
below.)
In the i.atcorr man page it says:
"If flag -r is used, the input raster data are treated as
reflectance. Otherwise, the input raster data are treated as
radiance values"
IIUC, your data is still in DN. You might want to try to transform
this into radiance values before sending it into i.atcorr.
Moritz
Thanks again.
Zofie
----------------------------------------
Version:
g.version -g
version=7.4.0RC1
date=2017
revision=exported
build_date=2017-11-18
build_platform=x86_64-pc-linux-gnu
build_off_t_size=8
----------------------------------------
Region:
g.region -p
projection: 1 (UTM)
zone: 33
datum: etrs89
ellipsoid: grs80
north: 6653695
south: 6643685
west: 256495
east: 266505
nsres: 10
ewres: 10
rows: 1001
cols: 1001
cells: 1002001
----------------------------------------
Input data: Sentinel2 L1C product B02 (tried with B01 too)
r.info <http://r.info> <http://r.info>
map=test_B02@p_Sentinel4Nature_S2_Oslo
+----------------------------------------------------------------------------+
| Map: test_B02@p_Sentinel4Nat Date: Wed Dec 6
12:06:39 2017
| Mapset: p_Sentinel4Nature_S2_Oslo Login of Creator:
stefan.blumentr
| Location: ETRS_33N
| DataBase: /data/grass
| Title:
S2A_OPER_PRD_MSIL1C_PDMC_20160907T044118_R008_V20160905T104022_2
| Timestamp: none
|----------------------------------------------------------------------------|
|
| Type of Map: raster Number of Categories: 0
| Data Type: CELL
| Rows: 1001
| Columns: 1001
| Total Cells: 1002001
| Projection: UTM (zone 33)
| N: 6653695 S: 6643685 Res: 10
| E: 266505 W: 256495 Res: 10
| Range of data: min = 1 max = 28000
|
| Data Description:
| generated by r.in.gdal
+---------------------------------------------------------------------
-------+
----------------------------------------
6s file:
25- geometrical conditions=Sentinel-2A
9 5 10.6728 10.73413 59.90647- month day hh.ddd longitude latitude
4 - atmospheric model=subarctic summer
3- aerosol model=urban
50- visibility [km] (aerosol model concentration) (this is
estimated, I also tried with AOD specified)
-0.055- mean target elevation above sea level [km]
-1000- sensor height
166- Sentinel2A Blue band B2 (440nm - 535nm)
----------------------------------------
Command:
i.atcorr input=test_B02@p_Sentinel4Nature_S2_Oslo range=1,28000
elevation=dem_10m_25833@p_Sentinel4Nature_S2_Oslo
parameters=/home/NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt>
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt>>
output=test_B02_atcorr
>Atmospheric correction...
>Atmospheric correction complete.
(I am not sure about the range parameter, tried with 0,255 too.
The DEM contains no NULLs. Also tried running with -r and -a
flags.)
----------------------------------------
Output:
r.info <http://r.info> <http://r.info>
map=test_B02_atcorr@p_Sentinel4Nature_S2_Oslo
+----------------------------------------------------------------------------+
| Map: test_B02_atcorr@p_Sentinel4N Date: Mon Dec 18
13:10:14 2017
| Mapset: p_Sentinel4Nature_S2_Oslo Login of Creator:
zofie.cimburova
| Location: ETRS_33N
| DataBase: /data/grass
| Title: test_B02_atcorr2
| Timestamp: none
|----------------------------------------------------------------------------|
|
| Type of Map: raster Number of Categories: 0
| Data Type: FCELL
| Rows: 1001
| Columns: 1001
| Total Cells: 1002001
| Projection: UTM (zone 33)
| N: 6653695 S: 6643685 Res: 10
| E: 266505 W: 256495 Res: 10
| Range of data: min = -nan max = -nan
|
| Data Description:
| generated by i.atcorr
|
| Comments:
| i.atcorr input="test_B02@p_Sentinel4Nature_S2_Oslo"
range=1,28\
| 000 elevation="dem_10m_25833@p_Sentinel4Nature_S2_Oslo"
para\
|
meters="/home/NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt>
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt
<http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt>>" o\
| utput="test_B02_atcorr2" rescale=0,255
|
+---------------------------------------------------------------------
-------+
On Fri, Dec 15, 2017 at 5:12 PM, Žofie Cimburová
<zoficimbur...@gmail.com <mailto:zoficimbur...@gmail.com>
<mailto:zoficimbur...@gmail.com
<mailto:zoficimbur...@gmail.com>>> wrote:
Dear Markus,
thanks for your reply, this is exactly what I need to know!
Best, Zofie
On Fri, Dec 15, 2017 at 5:09 PM, Markus Neteler
<nete...@osgeo.org <mailto:nete...@osgeo.org>
<mailto:nete...@osgeo.org <mailto:nete...@osgeo.org>>> wrote:
On Dec 15, 2017 3:54 PM, "Žofie Cimburová"
<zoficimbur...@gmail.com
<mailto:zoficimbur...@gmail.com> <mailto:zoficimbur...@gmail.com
<mailto:zoficimbur...@gmail.com>>> wrote:
>
> Dear all,
> I am trying to use i.atcorr (GRASS 7.4) to apply
atmospheric corrections for Sentinel 2 data. The documentation
provides a great help, but there are two points I am not sure
about - >
> - I don't need the atmospheric correction to be
applied to the whole scene, so I only imported a small clip of
the scene to GRASS. What longitude and latitude shall I then
specify in the 6S parameters?
I'd use the center coordinates of the clipped area.
> Or is it necessary to apply the corrections to the
entire scene?
No since it is a pixel based algorithm.
> - How can I estimate the value of visibility (aerosol
model concentration)?
There are AERONET data online somewhere which might be
the best
choice.
Markus
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