[GRASS-user] Color equalization after patching/mosaicking the satellite data from multiple scenes

[Nikos Alexandris]

* Sajid Pareeth <spareeth at gmail.com> [2016-12-30 16:34:23 +0100]:

>Hi all
>
>I have some data from different scenes of Landsat8 covering my area of
>interest. But after mosaicking, it clearly shows the border line and the
>difference in colors in the composites.

Dear Sajid,

some normalisation, before patching, is what "needs" to be done, I think.  Relative
normalisation here (either for images of different dates over the same
area, or neighbouring images of the same date).

I never finished implementing some very simple process as described in
user manual(s) for QuickBird2 imagery, if I remember well.

I have a draft module which I named i.radio.balance. In short:  the
major difference between two scenes of the same area is the solar
geometry.  This difference can be minimized by correcting imagery for
Earth-sun distance and solar zenith angle.

I can send you off-list, if you want, the on-going script (incomplete, yet well
documented I believe it to be).

Cheers, Nikos


ps-  We need more advanced algorithms for such tasks (ie relative
radiomatric normalisation).




>For example I am attaching two cases, one from *Sentinel2* and another from
>*Landsat8*.
>
>I mosaicked two scenes of sentinel taken on the *same day,- November 19
>2016*, and tried following commands to get a composite.
>
>i.colors.enhance blue=S2A_B02 green=S2A_B8A.hpf red=S2A_B11.hpf
>> r.composite blue=S2A_B02.hpf green=S2A_B8A.hpf red=S2A_B11
>> output=test_118A02
>>
>
>And it works perfect, there is no sign that the image is from two scenes
>(attached - S2_19Nov2016comp_118A02.jpg ).
>
>But in the case of L8, it is more complicated as the data is coming from
>three scenes. Two scenes are from the same orbit and third from adjacent
>which has a different date.
>For each  scene, there are two acquisitions in November 2016 (Total six
>images in November 2016 for this g.region).
>Hence I used r.patch and r.series to create a November month composite and
>with this, the color composite looks really bad.
>
>i.colors.enhance blue=L8_B02.hpf green=L8_B05.hpf red=L8_B06.hpf
>> r.composite blue=L8_B02.hpf green=L8_B05.hpf red=L8_B06.hpf output=test_652
>>
>
>Please see attached "L8_Nov2016_comp_652.jpg"
>
>Is there anything I miss here to obtain a good composite over multiple
>scenes taken from different dates, but from the same month?
>
>
>Regards
>
>Sajid



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Nikos Alexandris | Remote Sensing & Geomatics
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