[GRASS-user] Landsat 8 Workflow for Grass 7.0.0RC2

[Nikos Alexandris]

Paul Shapley wrote:

> I want to use the following Landsat 8 workflow to obtain some 
> pansharpened
> images but have a problem when i convert the DN values to 8bit for
> pansharpening. Here is my preferred workflow in Grass 7.0.0RC2.

> ·                     r.in.gdal (success)
> ·                     i.landsat.toar (success)
> ·                     r.rescale bands 432 & 8 (convert reflectance 
> 'DN'
> values to 0-255, 8bit)

> ·                     i.pansharpen bands 432 with 8
> ·                     r.rescale (convert 0-255 values back to 
> reflectance
> 'DN)
> ·                     i.colors.enhance (pansharp bands)
> ·                     d.rgb

> My question...is this a valid workflow? because i'm getting the same 
> two
> errors below and the images when displayed look solid grey when 
> viewed with
> d.rgb:

Paul,

just some thoughts:

- why mix the term "Digital Number (DN)" with Reflectance?  DN's are 
(supposed to be) the result of the quantisation (and calibration) of the 
energy that hits the sensor.  And Reflectance (unitless) is the result 
of radiometrically processing the DN values.

- Not sure if the values of the end-product, as in the work-flow you 
outline above, can be called Reflectance.

- Landsat8 is 16-bit.  Once you downscale down to 8-bit, how would you 
come back to the 16-bit details?  I think the radiometric detail is 
lost.

Instead, import > DN to ToAR > Pan-Sharpen with i.fusion.hpf (to not 
loose the fine digits which are important if you seek for more than just 
sharp visuals for viewing purposes).

Best, Nikos