[GRASS-user] Estimating Albedo from Landsat

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Wed Sep 15 10:04:42 EDT 2010


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 :-)






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