I'll have to check but I believe I used constant visibility for the 6S correction but, I did use an elevation map from SRTM. Of course the area is rather flat (a wetland).
Daniel On Tue, May 31, 2011 at 11:35 AM, Markus Metz <[email protected]> wrote: > On Sun, May 29, 2011 at 8:16 PM, Daniel Victoria > <[email protected]> wrote: >> I'm also struggling with i.atcorr for Landsat. A friend of my >> corrected some TM images using the Flash module in ENVI (based on >> modtran) and I tried to correct the same images using 6S in grass >> (i.atcorr). We both used the same radiance images that had some >> problems with a few negative values in water areas. I set the negative >> values to 0. >> >> After correcting the TM images in Grass I created 6000 random point in >> order to compare the images (flash vs. 6s). The attached graph shows >> the density plot (~histogram) for each band (band 6 is actually TM >> band7). For all images, value have been scaled from 0 to 1. Black line >> is radiance, red is 6S and blue is flash. What we see is that for >> bands 4, 5 and 7 there are no big differences but, for bands 1, 2 and >> 3, the correction done by flash is more pronounced. >> >> Now, what I don't know: >> 1) Is this type of analysis (looking at the image histogram) OK? >> 2) Should atmospheric correction change the histogram? >> 3) For i.atcorr I get a sort of "linear" relation between radiance & >> reflectance. That is, for each radiance there is only one value for >> reflectance. But the flash correction gives a point cloud when I >> compare radiance & reflectance (more than one reflectance value for >> the same radiance). What is the expected behavior? > > If you use global values for elevation and visibility, you will only > one output value for each input value. If you use an elevation and/or > visibility map as additional input (granted that the values in these > maps are not constants), you may get point clouds, i.e. several > different output values for the same input value if this input value > occurs more than once and either elevation or visibility differ > between the occurences. > > Markus M > >> >> I'm using Grass 7 svn from about 2 weeks ago. The images are from the >> Pantanal wetland in Brazil in the dry period (still lots of water >> there). For 6S the settings are: Tropical atmosphere, continental >> aerosol mode, 20km visibility. >> >> Thanks and cheers >> Daniel >> >> >> On Fri, May 27, 2011 at 7:34 PM, Juan Benavides Duque <[email protected]> >> wrote: >>> I'm sending the code I used to run the i.atcorr module (including the >>> i.landsat.toar transformation) >>> >>> (I also used the code sent by Yann Chemin (May 23) with the same results) >>> >>> Of two files attached one has the code and other one the univariate stats >>> output of the band 1 TOAR raster for one of the 1986 scenes >>> >>> A copy of the original landsat used have been placed temporarily at the >>> following location " assets " >>> >>> hope somebody can help >>> >>> >>> thanks >>> >>> juan >>> >>> >>> I'm using a desktop running Ubuntu 10.10 with a 64bit Intel(R) Core(TM) i7 >>> CPU 860 @ 2.80GHz >>> >>> >>> >>> >>> 2011/5/27 Gaspar Reyes Póndigo <[email protected]> >>>> >>>> I had same problem, i.atcorr not work with landsat 5TM band 1, 2 and >>>> sometimes with band 3 >>>> I tried i.atcorr in different versions of grass, this is my results: >>>> >>>> 1. GRASS-6.4.1-2 under Mac Snow-Leopard 10.6.7: Not work band 1, 2, and >>>> sometimes with band 3 (for years 1992, 1993, 1995 and 1997). >>>> 2. GRASS-6.5. revision 46428 compiled in Mac Snow-Leopard 10.6.7: Not work >>>> band 1, 2, and sometimes with band 3 (for years 1992, 1993, 1995 and 1997) >>>> 3. GRASS-6.5svn45719(2011) under Microsoft Windows Xp sp3: All the bands >>>> work,THIS IS VERY RARE >>>> >>>> My images landsat 5 TM are from Tonameca, Oaxaca, México of years 1985 to >>>> 1999, and 2010 to 2011 (one image series for year), i am work with AOD and >>>> visibility value, and convert manually DN to radiance (a). >>>> >>>> (a) Lλ = [(LMAXλ − LMINλ) / (Qcalmax − Qcalmin)] (Qcal − Qcalmin) + LMINλ >>>> >>>> Gaspar Reyes Póndigo >>>> Universidad del Mar, Oaxaca, México >>>> Campus Puerto-Ángel >>>> Carretera principal Puerto Ángel Zipolite km 1.5 >>>> C.P. 70902 >>>> >>>> ------------------------------------------------------------------- >>>> >>>> Message: 1 >>>> >>>> Date: Fri, 27 May 2011 08:53:32 +0530 >>>> >>>> From: "Chemin, Yann (IWMI)" <[email protected]> >>>> >>>> Subject: RE: [GRASS-user] Re: i.atcorr returns all NULL values >>>> >>>> To: "Juan Benavides Duque" <[email protected]>, >>>> >>>> <[email protected]> >>>> >>>> Cc: Markus Metz <[email protected]>, Elena Mezzini >>>> >>>> <[email protected]> >>>> >>>> Message-ID: >>>> >>>> <[email protected]> >>>> >>>> Content-Type: text/plain; charset="us-ascii" >>>> >>>> Hi Juan, >>>> >>>> >>>> >>>> Can you please give the download link for your images, >>>> >>>> Could you also check the output of i.landsat.toar for them and tell if >>>> >>>> reflectance ranges are valid/logic. >>>> >>>> >>>> >>>> Thank you, >>>> >>>> Yann >>>> >>>> >>>> >>>> From: Juan Benavides Duque [mailto:[email protected]] >>>> >>>> Sent: Thursday, May 26, 2011 11:38 PM >>>> >>>> To: Chemin, Yann (IWMI) >>>> >>>> Cc: Markus Metz; Elena Mezzini >>>> >>>> Subject: Re: [GRASS-user] Re: i.atcorr returns all NULL values >>>> >>>> >>>> >>>> >>>> I tried Yann's code for the i.atcorr on some Landsat TM5 images >>>> >>>> It worked very nice for images taken after 1995 but before that still >>>> >>>> returns null values when running i.atcorr for bands 1 and 2 >>>> >>>> I used TM5 scenes from the same location for 1986, 1989, and 1996 and >>>> >>>> the first two (1986 and 1989) had the same problem with the null >>>> >>>> values... >>>> >>>> sorry I can provide a way to fix it but I hope somebody will >>>> >>>> juan c >>>> >>>> >>>> >>>> >>>> >>>> >>>> On Tue, May 24, 2011 at 3:49 AM, Chemin, Yann (IWMI) >>>> >>>> <[email protected]> wrote: >>>> >>>> Each created visibility map holds only one value r.mapcalc >>>> >>>> expression="visibility=${vis_list[$i]}" --overwrite so why not just use >>>> >>>> this visibility value as input in the >parameter file instead of >>>> >>>> creating a map where all cells have the same value? >>>> >>>> Yes, this is a valid point, the script is designed to (hopefully soon) >>>> >>>> encompass raster maps of visibility data (maybe interpolated...), so >>>> >>>> this is a placeholder for the next steps. >>>> >>>> >>>> -----Original Message----- >>>> >>>> From: Markus Metz [mailto:[email protected]] >>>> >>>> Sent: Tuesday, May 24, 2011 12:52 PM >>>> >>>> To: Chemin, Yann (IWMI) >>>> >>>> Cc: [email protected]; Elena Mezzini; Markus Neteler >>>> >>>> Subject: Re: [GRASS-user] Re: i.atcorr returns all NULL values >>>> >>>> On Mon, May 23, 2011 at 9:36 PM, Markus Neteler <[email protected]> >>>> >>>> wrote: >>>> >>>> Hi Yann, >>>> >>>> On Mon, May 23, 2011 at 5:07 AM, Chemin, Yann (IWMI) >>>> >>>> <[email protected]> wrote: >>>> >>>> p192 r030 image of July 2003 of Italy (L5TM) successfully corrected >>>> >>>> for band 1 and 2. >>>> >>>> The following script works well in GRASS GIS Trunk SVN. >>>> >>>> (better send as attachment since a series of line breaks got broken) >>>> >>>> ... >>>> >>>> # For i.atcorr scripting >>>> >>>> #----------------------------------------------------- >>>> >>>> vis_list=(10 10 8 9.7 15 8 7 10 10 9.7 12 9.7 7 12 12 12 3 15 12 9.7 >>>> >>>> 6 15) vis_len=${#vis_list[*]} echo $vis_len >>>> >>>> ... this is not clear to me: why so many values and where do they >>>> >>>> originate from? Since we have only 6 channels to work with... >>>> >>>> Moreover, how can it be possible that visibility is different for >>>> >>>> different channels of the same scene? From the documentation it seems >>>> >>>> that visibility is related to aerosol concentration at 550nm which can >>>> >>>> not possibility be different for different bands of the same scene. >>>> >>>> Each created visibility map holds only one value r.mapcalc >>>> >>>> expression="visibility=${vis_list[$i]}" --overwrite so why not just use >>>> >>>> this visibility value as input in the parameter file instead of creating >>>> >>>> a map where all cells have the same value? >>>> >>>> Markus M >>>> >>>> _______________________________________________ >>>> >>>> grass-user mailing list >>>> >>>> [email protected] >>>> >>>> http://lists.osgeo.org/mailman/listinfo/grass-user >>>> >>>> >>>> >>>> -------------- next part -------------- >>>> >>>> An HTML attachment was scrubbed... >>>> >>>> >>>> URL: http://lists.osgeo.org/pipermail/grass-user/attachments/20110527/211bcf66/attachment-0001.html >>>> >>>> _______________________________________________ >>>> grass-user mailing list >>>> [email protected] >>>> http://lists.osgeo.org/mailman/listinfo/grass-user >>>> >>> >>> >>> _______________________________________________ >>> grass-user mailing list >>> [email protected] >>> http://lists.osgeo.org/mailman/listinfo/grass-user >>> >>> >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> >> > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
