[GRASS-user] Re: i.atcorr returns all NULL values

[Markus Metz]

On Sun, May 29, 2011 at 8:16 PM, Daniel Victoria
<daniel.victoria at gmail.com> 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 <jbenavid at siu.edu> 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 <gos47 at hotmail.com>
>>>
>>> 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)" <Y.Chemin at cgiar.org>
>>>
>>> Subject: RE: [GRASS-user] Re: i.atcorr returns all NULL values
>>>
>>> To: "Juan Benavides Duque" <jbenavid at siu.edu>,
>>>
>>> <grass-user at lists.osgeo.org>
>>>
>>> Cc: Markus Metz <markus.metz.giswork at googlemail.com>, Elena Mezzini
>>>
>>> <elena.mezzini at gmail.com>
>>>
>>> Message-ID:
>>>
>>> <001F233294EA894387CFDAADAB87DE25085063E9 at iwmix.IWMI.CGIARAD.ORG>
>>>
>>> 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:jbenavid at siu.edu]
>>>
>>> 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)
>>>
>>> <Y.Chemin at cgiar.org> 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:markus.metz.giswork at googlemail.com]
>>>
>>> Sent: Tuesday, May 24, 2011 12:52 PM
>>>
>>> To: Chemin, Yann (IWMI)
>>>
>>> Cc: grass-user at lists.osgeo.org; 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 <neteler at osgeo.org>
>>>
>>> wrote:
>>>
>>> Hi Yann,
>>>
>>> On Mon, May 23, 2011 at 5:07 AM, Chemin, Yann (IWMI)
>>>
>>> <Y.Chemin at cgiar.org> 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
>>>
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>>
>>
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