[GRASS-user] i.atcorr with Sentinel2
Moritz Lennert
mlennert at club.worldonline.be
Mon Dec 18 06:35:47 PST 2017
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> map=test_B02 at p_Sentinel4Nature_S2_Oslo
> +----------------------------------------------------------------------------+
> | Map: test_B02 at 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 at p_Sentinel4Nature_S2_Oslo range=1,28000
> elevation=dem_10m_25833 at p_Sentinel4Nature_S2_Oslo
> parameters=/home/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> map=test_B02_atcorr at p_Sentinel4Nature_S2_Oslo
> +----------------------------------------------------------------------------+
> | Map: test_B02_atcorr at 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 at p_Sentinel4Nature_S2_Oslo" range=1,28\
> | 000 elevation="dem_10m_25833 at p_Sentinel4Nature_S2_Oslo" para\
> | meters="/home/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
> <zoficimburova at gmail.com <mailto:zoficimburova at 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 <neteler at osgeo.org
> <mailto:neteler at osgeo.org>> wrote:
>
>
> On Dec 15, 2017 3:54 PM, "Žofie Cimburová"
> <zoficimburova at gmail.com <mailto:zoficimburova at 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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