Re: i.atcorr with Sentinel2
Moritz Lennert <[email protected]>
| Newsgroups | gmane.comp.gis.grass.user |
|---|---|
| Message-ID | <[email protected]> |
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 > <[email protected] <mailto:[email protected]>> 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 > <[email protected] <mailto:[email protected]> > <mailto:[email protected] > <mailto:[email protected]>>> 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 > <[email protected] <mailto:[email protected]> > <mailto:[email protected] <mailto:[email protected]>>> wrote: > > > On Dec 15, 2017 3:54 PM, "Žofie Cimburová" > <[email protected] > <mailto:[email protected]> <mailto:[email protected] > <mailto:[email protected]>>> 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 > > > > > > _______________________________________________ > grass-user mailing list > [email protected] <mailto:[email protected]> > https://lists.osgeo.org/mailman/listinfo/grass-user > <https://lists.osgeo.org/mailman/listinfo/grass-user> > > > > _______________________________________________ grass-user mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/grass-user