[GRASS-user] i.atcorr for GeoEye-1 and Worldview-3

Nikos Alexandris nik at nikosalexandris.net
Wed Jun 3 20:48:13 PDT 2015

* Kamhul Camhol <monk_purple at yahoo.com> [2015-06-04 02:27:58 +0000]:

> Dear Nikos,

Hi Kamhul,

> Thanks for the advice! The imagery are Ortho-Ready Standard 2A, already radiometrically and sensor-corrected 

Likely the products are delivered in Digital Numbers (DN). These
DNs are indeed "radiometrically corrected image pixels". They are not,
however, radiance or reflectance.  You need to convert first the
quantized DNs to some physical quantity before doing any further
radiometric processing (that includes atmospheric "corrections" as far
as understand) or working with vegetation indices. Or comparing images.

I have collected my notes when working with high resolution imagery in
the Wiki [0, 1, 2].  There are links to very nice readings, i.e. [3].

> but not atmospherically and geometrically corrected.

Just two notes here: if the image is clear, one can work on without "correcting" for
atmospheric effects. If the image is capturing a flat-land, maybe
applying the accompanied RPCs (via gdal) is enough.

>Are they already in radiance or reflectance values?

Very unlikely.

> Sometimes, I am confused as radiometric correction appears to be interchanged or taken similarly with atmospheric correction.

Please go through some of the readings.  They offer the required
clarifications. It would be useful to retrieve relevant documentation
for WorldView 3.

> Anyway, of course I would be willing to support the testing as you said. May I know how this is done?

Will try to find some time to reply properly for this.  In the end, we can
improve the wiki-pages as well.

Cheers, Nikos

[0] http://grasswiki.osgeo.org/wiki/QuickBird
[1] http://grasswiki.osgeo.org/wiki/WorldView
[2] http://grasswiki.osgeo.org/wiki/IKONOS

>      On Thursday, June 4, 2015 12:28 AM, Nikos Alexandris <nik at nikosalexandris.net> wrote:
>  * Kamhul Camhol <monk_purple at yahoo.com> [2015-06-03 04:56:37 +0000]:
> > Hello. I'm quite new with GRASS but I need to atmospherically process high-resolution imagery with i.atcorr. I have three images Quickbird, GeoEye-1 and Worldview-3 imagery of a single scene across three time periods.
> Hi!
> You would need, I think, to convert the raw Digital Numbers first to
> radiance/reflectance values. Please have a look at [0][1].
> > For Quickbird, I have all the data needed but basing from the following manual GRASS GIS manual: i.atcorr  there appears to be novalues for two required inputs for GeoEye-1 and Worldview-3.
> I have prepared months ago the numbes for QB2 and WV2 Yet, there has been no successful test so far (from my side at
> least). I need to try again :-/. Are you willing to support testing?
> > These are geometrical conditions and band. May I know if GRASS has updated the i.atcorrmanual to include these sensors as well?
> > Can I use the values ofWorldview-2 for Worldview-3?
> I think not. We need to get the radiometric response values for WV3.
> Then we can prepare the required data for i.atcorr.  But, as with the
> other two, it needs testing.
> > Or is there any other way to do the atmospheric correction for these two sensors?
> There are other tools that could do this. I think ORFEO ToolBox is one
> (from which I stole the numbers for QB2 back then).
> Yet, having this option in GRASS will make the workflow easier. We need
> it.
> Nikos

Nikos Alexandris | Remote Sensing Scientist, Dr
Themidos 3, 42100, Trikala, Greece
GPG Key Fingerprint 6F9D4506F3CA28380974D31A9053534B693C4FB3 

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