[GRASS-user] Low reflectance values with i.atcorr and Landsat 8

Yann Chemin ychemin at gmail.com
Tue Jun 16 20:45:35 PDT 2015


Something is fishy here, reflectance values should always be within 0-1
range.

Please manually remove all values outside of that range (use r.mapcalc) and
make a histogram of your TOAR band. if the histogram is of expected shape,
and is not truncated at 1.0 threshold then you are OK. if there is a
problem here, that means the TOAR processing had an issue. Stretching
output from an unknown histogram skewness could be giving you funny results.


On Mon, Jun 15, 2015 at 6:47 PM Micha Silver <micha at arava.co.il> wrote:

> On 6/15/2015 3:25 PM, John, Lisa wrote:
>
> Hi Micha,
>
> did you refer to the input range?
>
> Yes, the input range.
>
>  I did so and checked bands 1-9 with r.info -r. Top of atmosphere
> reflectance values are all in the range of -0.01 - 2.12. The negative value
> seems to be a outlier and I check in addition with the range 0-2.12.
> I used these values for the input range in i.atcorr -r and used 0,1 as
> output range.
>
> I meant in the first i.landsat.toar step. The input (DN) values should be
> up to 700 or so. Landsat 8, with its 12 bit data can have max DN values of
> 4096. But I didn't use that full range, rather the actual DN range of the
> original images.
>
>
>  However I get even smaller reflectance values (0.15 respectively 0.29 for
> vegetation in band5)
>
> Regards, Lisa.
>
>
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