<div dir="ltr"><div>Dear Moritz,</div><div><br></div><div>According to <a href="https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/product-types">https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/product-types</a> , the L1C product I am using already is in top of atmosphere reflectance, so this should not be the problem (?). </div><div>I tried running i.atcorr both with and without the -r flag.</div><div><br></div><div>Zofie</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Dec 18, 2017 at 3:35 PM, Moritz Lennert <span dir="ltr"><<a href="mailto:mlennert@club.worldonline.be" target="_blank">mlennert@club.worldonline.be</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">On 18/12/17 13:14, Žofie Cimburová wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi all,<br>
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.)<br>
</blockquote>
<br></span>
In the i.atcorr man page it says:<br>
<br>
"If flag -r is used, the input raster data are treated as reflectance. Otherwise, the input raster data are treated as radiance values"<br>
<br>
IIUC, your data is still in DN. You might want to try to transform this into radiance values before sending it into i.atcorr.<br>
<br>
Moritz<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
<br>
Thanks again.<br>
Zofie<br>
<br>
------------------------------<wbr>----------<br>
Version:<br>
g.version -g<br>
version=7.4.0RC1<br>
date=2017<br>
revision=exported<br>
build_date=2017-11-18<br>
build_platform=x86_64-pc-linux<wbr>-gnu<br>
build_off_t_size=8<br>
<br>
------------------------------<wbr>----------<br>
Region:<br>
g.region -p<br>
projection: 1 (UTM)<br>
zone: 33<br>
datum: etrs89<br>
ellipsoid: grs80<br>
north: 6653695<br>
south: 6643685<br>
west: 256495<br>
east: 266505<br>
nsres: 10<br>
ewres: 10<br>
rows: 1001<br>
cols: 1001<br>
cells: 1002001<br>
<br>
------------------------------<wbr>----------<br>
Input data: Sentinel2 L1C product B02 (tried with B01 too)<br>
</div></div><a href="http://r.info" rel="noreferrer" target="_blank">r.info</a> <<a href="http://r.info" rel="noreferrer" target="_blank">http://r.info</a>> map=test_B02@p_Sentinel4Nature<wbr>_S2_Oslo<span class=""><br>
+---------------------------<wbr>------------------------------<wbr>-------------------+<br>
| Map: test_B02@p_Sentinel4Nat Date: Wed Dec 6 12:06:39 2017<br>
| Mapset: p_Sentinel4Nature_S2_Oslo Login of Creator: stefan.blumentr<br>
| Location: ETRS_33N<br>
| DataBase: /data/grass<br>
| Title: S2A_OPER_PRD_MSIL1C_PDMC_20160<wbr>907T044118_R008_V20160905T1040<wbr>22_2<br>
| Timestamp: none<br>
|---------------------------<wbr>------------------------------<wbr>-------------------|<br>
|<br>
| Type of Map: raster Number of Categories: 0<br>
| Data Type: CELL<br>
| Rows: 1001<br>
| Columns: 1001<br>
| Total Cells: 1002001<br>
| Projection: UTM (zone 33)<br>
| N: 6653695 S: 6643685 Res: 10<br>
| E: 266505 W: 256495 Res: 10<br>
| Range of data: min = 1 max = 28000<br>
|<br>
| Data Description:<br>
| generated by r.in.gdal<br>
+---------------------------<wbr>------------------------------<wbr>-------------------+<br>
<br>
------------------------------<wbr>----------<br>
6s file:<br></span>
25- geometrical conditions=Sentinel-2A<br>
9 5 10.6728 10.73413 59.90647- month day hh.ddd longitude latitude<span class=""><br>
4 - atmospheric model=subarctic summer<br>
3- aerosol model=urban<br></span>
50- visibility [km] (aerosol model concentration) (this is estimated, I also tried with AOD specified)<br>
-0.055- mean target elevation above sea level [km]<br>
-1000- sensor height<br>
166- Sentinel2A Blue band B2 (440nm - 535nm)<br>
<br>
------------------------------<wbr>----------<br>
Command:<br>
i.atcorr input=test_B02@p_Sentinel4Natu<wbr>re_S2_Oslo range=1,28000 elevation=dem_10m_25833@p_Sent<wbr>inel4Nature_S2_Oslo parameters=/home/<a href="http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt" rel="noreferrer" target="_blank">NINA.NO/zofie<wbr>.cimburova/Sentinel4Nature/<wbr>DATA/6s.txt</a> <<a href="http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt" rel="noreferrer" target="_blank">http://NINA.NO/zofie.cimburov<wbr>a/Sentinel4Nature/DATA/6s.txt</a>> output=test_B02_atcorr<span class=""><br>
>Atmospheric correction...<br>
>Atmospheric correction complete.<br>
<br>
(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.)<br>
<br>
------------------------------<wbr>----------<br>
Output:<br>
</span><a href="http://r.info" rel="noreferrer" target="_blank">r.info</a> <<a href="http://r.info" rel="noreferrer" target="_blank">http://r.info</a>> map=test_B02_atcorr@p_Sentinel<wbr>4Nature_S2_Oslo<span class=""><br>
+---------------------------<wbr>------------------------------<wbr>-------------------+<br>
| Map: test_B02_atcorr@p_Sentinel4N Date: Mon Dec 18 13:10:14 2017<br>
| Mapset: p_Sentinel4Nature_S2_Oslo Login of Creator: zofie.cimburova<br>
| Location: ETRS_33N<br>
| DataBase: /data/grass<br>
| Title: test_B02_atcorr2<br>
| Timestamp: none<br>
|---------------------------<wbr>------------------------------<wbr>-------------------|<br>
|<br>
| Type of Map: raster Number of Categories: 0<br>
| Data Type: FCELL<br>
| Rows: 1001<br>
| Columns: 1001<br>
| Total Cells: 1002001<br>
| Projection: UTM (zone 33)<br>
| N: 6653695 S: 6643685 Res: 10<br>
| E: 266505 W: 256495 Res: 10<br>
| Range of data: min = -nan max = -nan<br>
|<br>
| Data Description:<br>
| generated by i.atcorr<br>
|<br>
| Comments:<br>
| i.atcorr input="test_B02@p_Sentinel4Nat<wbr>ure_S2_Oslo" range=1,28\<br>
| 000 elevation="dem_10m_25833@p_Sen<wbr>tinel4Nature_S2_Oslo" para\<br></span>
| meters="/home/<a href="http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt" rel="noreferrer" target="_blank">NINA.NO/zofie.ci<wbr>mburova/Sentinel4Nature/DATA/<wbr>6s.txt</a> <<a href="http://NINA.NO/zofie.cimburova/Sentinel4Nature/DATA/6s.txt" rel="noreferrer" target="_blank">http://NINA.NO/zofie.cimburov<wbr>a/Sentinel4Nature/DATA/6s.txt</a>><wbr>" o\<br>
| utput="test_B02_atcorr2" rescale=0,255<br>
|<br>
+---------------------------<wbr>------------------------------<wbr>-------------------+<span class=""><br>
<br>
<br>
<br>
On Fri, Dec 15, 2017 at 5:12 PM, Žofie Cimburová <<a href="mailto:zoficimburova@gmail.com" target="_blank">zoficimburova@gmail.com</a> <mailto:<a href="mailto:zoficimburova@gmail.com" target="_blank">zoficimburova@gmail.co<wbr>m</a>>> wrote:<br>
<br>
Dear Markus,<br>
thanks for your reply, this is exactly what I need to know!<br>
<br>
Best, Zofie<br>
<br>
On Fri, Dec 15, 2017 at 5:09 PM, Markus Neteler <<a href="mailto:neteler@osgeo.org" target="_blank">neteler@osgeo.org</a><br></span><span class="">
<mailto:<a href="mailto:neteler@osgeo.org" target="_blank">neteler@osgeo.org</a>>> wrote:<br>
<br>
<br>
On Dec 15, 2017 3:54 PM, "Žofie Cimburová"<br></span><span class="">
<<a href="mailto:zoficimburova@gmail.com" target="_blank">zoficimburova@gmail.com</a> <mailto:<a href="mailto:zoficimburova@gmail.com" target="_blank">zoficimburova@gmail.co<wbr>m</a>>> wrote:<br>
><br>
> Dear all,<br>
> 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 - ><br>
> - 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?<br>
<br>
I'd use the center coordinates of the clipped area.<br>
<br>
> Or is it necessary to apply the corrections to the entire scene?<br>
<br>
No since it is a pixel based algorithm.<br>
<br>
> - How can I estimate the value of visibility (aerosol model concentration)? <br>
There are AERONET data online somewhere which might be the best<br>
choice.<br>
<br>
Markus<br>
<br>
<br>
<br>
<br>
<br></span><span class="">
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</span></blockquote>
<br>
<br>
</blockquote></div><br></div>