[GRASS-user] Estimating Albedo from Landsat
nikos.alexandris at felis.uni-freiburg.de
Wed Sep 15 10:04:42 EDT 2010
> > # 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 :-)
i.landsat.acca -5 -2 -s band_prefix=landsat_postfire_east_sterea_ellas.toar
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
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
# withous the "-s"
i.landsat.acca -5 -2 band_prefix=landsat_postfire_east_sterea_ellas.toar
Superb! This detects clouds (not the shadows though) very precise I dare to
# with "-f"
not sure about the real differences with the previous command. Look fine
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