i.atcorr RapidEye band1

[chrisraa]

Dear grass gis team, actually I am working with several RapidEye (product Type L3A) acquisitions, in order to pre-process them for classification. It occurred to me that in some cases i.atcorr creates a results for the first band (blue), which seems to be “biased”. I applied i.atcorr on different machines and used different versions of Grass, but the issue is persistent.

Grass versions I tried on a Windows7 Professional, 64-bit system: 6.4.4, 7.0.0beta4 and 7.1svn

Input text file values I used:

13

5 25 12.8 52.09413 -10.22328

2

2

0

0.161

-0.253824

-1000

88

For the input imagery and its range a used the min and max values of the radiance image. As input altitude raster map a 5m DEM was used and for rescale output the range 0,1.

Please let me know if you need further information! Many thanks in advance!! Christoph

[chrisraa]

example_i.atcorr_RapidEye_band1

[martinl]

Ticket retargeted after milestone closed

[neteler]

I think I identified the issue:

The filter function values for RapidEye do not have the needed precision (only 2 digits!):

compare:

​https://trac.osgeo.org/grass/browser/grass/trunk/imagery/i.atcorr/sensors_csv/rapideye.csv

to e.g.

​https://trac.osgeo.org/grass/browser/grass/trunk/imagery/i.atcorr/sensors_csv/geoeye1.csv

We need a higher resolution rapideye.csv

[craab]

I found more precise values here:

​https://resa.planet.com/files/2014-06/Spectral_Response_Curves.pdf

I updated the rapideye.csv file, as well as the iwave.cpp file according the provided filter curve data.
Please see the provided diff file.

Best, Christoph

[neteler]

Replying to craab:

I found more precise values here:

​https://resa.planet.com/files/2014-06/Spectral_Response_Curves.pdf

I updated the rapideye.csv file, as well as the iwave.cpp file according the provided filter curve data.
Please see the provided diff file.

This is great, thanks. Uploaded to trunk for testing in r70078.

Later to be backported once it is known to work ok (please report here).

[craab]

I tested the adjustment and it works, but it is not part of the solution either. However, I traced back the problem to the optical thickness value, which was to high:

(​https://www.rese-apps.com/pdf/atcor3_manual.pdf , page 19)

"If the visibility is assumed too low (optical thickness too high) the path radiance becomes high, and this may cause a physically unreasonable negative surface refectance. Therefore, dark surfaces of low refectance, and correspondingly low radiance c0+c1DN, are especially sensitive in this respect."

I guess the ticket can be closed and I will try to put together a paragraph for the manual.

[neteler]

Replying to craab:

I tested the adjustment and it works,

I have backported it in r71053.

but it is not part of the solution either. However, I traced back the problem to the optical thickness value, which was to high:

(​https://www.rese-apps.com/pdf/atcor3_manual.pdf , page 19)

"If the visibility is assumed too low (optical thickness too high) the path radiance becomes high, and this may cause a physically unreasonable negative surface refectance. Therefore, dark surfaces of low refectance, and correspondingly low radiance c0+c1DN, are especially sensitive in this respect."

I guess the ticket can be closed and I will try to put together a paragraph for the manual.

Please consider to provide a manual text snippet, even here or as a patch to the HTML page.

[neteler]

Ticket retargeted after milestone closed

[martinl]

What is status of this issue?

[neteler]

Replying to martinl:

What is status of this issue?

The promised text snippet for the manual did not arrive yet...

[martinl]

Ticket retargeted after milestone closed