[GRASS-user] Estimating Albedo from Landsat

[Nikos Alexandris]

Nikos:

> > > # so, here it goes... seems to run fine
> > > i.landsat.toar band_prefix=landsat_postfire_east_sterea_ellas
> > > method=uncorrected sensor=5 date=2007-09-05 solar_elevation=52.4986238
> > > product_date=2007-09-05
> > 
> > ...
> > 
> > > r.info landsat_postfire_east_sterea_ellas.toar.6 -r
> > > min=203.36601783578
> > > max=319.083636050686
> > > 
> > > No way the min value is true ( 203 K = -70.15 C -- irrational for
> > > Greece - for the moment! -)
> > > 
> > > The max value (319 K = 45.85 C) seems to fit for Greece but not for
> > > September! Maybe for July/August.
> > 
> > looking at the image/histogram again those min and max are outliers I
> > guess. The main body of information starts at ~280 K (6.85 C) and stops
> > at ~307 K (33.85 C).
> > 
> > I am not sure how to explain the min < 270 K  (those values lie mostly
> > within water bodies), but the max > 310 K areas are burned surfaces (a
> > few days old burn scars) which will explain the 45 C (at surface) in a
> > September day in Greece.
> > 
> > So, those values seem rational after all.
> 
> And, of course, an even better look reveals that those mins are the clouds
> :-)
> 
> # acca
> i.landsat.acca -5 -2 -s band_prefix=landsat_postfire_east_sterea_ellas.toar
> output=landsat_postfire_east_sterea_ellas.toar.acca
> 
> Pass one processing ...
>   PRELIMINARY SCENE ANALYSIS
>     Desert index:  0.975
>     Snow cover  :  0.001 %
>     Cloud cover :  12.856 %
>     Temperature of all clouds
>       Maximum: 299.82 K
>       Mean   : 251.23 K
>       Minimum: 203.37 K
>   HISTOGRAM CLOUD SIGNATURE
>       Histogram classes:  100
>       Mean temperature:   254.32 K
>       Standard deviation: 15.99
>       Skewness:           3298.36
>       97.50 percentile:   292.86 K
>       83.50 percentile:   276.87 K
> Pass two processing ...
> 
> 
> Finds clouds, shadows but includes too many irrelevant pixels -- bad result
> here :-(
> 
> # withous the "-s"
> i.landsat.acca -5 -2 band_prefix=landsat_postfire_east_sterea_ellas.toar
> output=landsat_postfire_east_sterea_ellas.toar.acca --o
> 
> Superb! This detects clouds (not the shadows though) very precise I dare to
> say :D
> 
> # with "-f"
> not sure about the real differences with the previous command. Look fine
> though :-)

OK, there is some salt and pepper but this can be removed by some filtering. 
It can be considered acceptable (?). Maybe I should post a screenshot 
(...later I'll try out the NC landsat5 image as well).