[GRASS-user] low radiance values after i.atcor and i.topo.corr

[maning sambale]

Hi,

After implementing gain and bias correction and topographic
correction, I get very low values for landsat data data
for example range of values of band1:

GRASS 6.3.1svn (p112r056):~ > r.info lsat7_2000.toar.1 -r
min=0.030303
max=0.372067
[Raster MASK present]
GRASS 6.3.1svn (p112r056):~ > r.info tcor.lsat7_2000.toar.1 -r
min=0.039443
max=0.442334

Running these range of values to an i.cluster reports very low separability:

means and standard deviations for 3 bands

 means     0.00   0.00   0.00
 stddev    0.06   0.00   0.00


initial means for each band

class 1     -0.05   0.00   0.00
class 2     -0.05   0.00   0.00
class 3     -0.05   0.00   0.00
class 4     -0.05   0.00   0.00
class 5     -0.04   0.00   0.00
class 6     -0.04   0.00   0.00
class 7     -0.04   0.00   0.00
class 8     -0.04   0.00   0.00
class 9     -0.03   0.00   0.00
class 10    -0.03   0.00   0.00
class 11    -0.03   0.00   0.00

...  "More output here but mostly 0 value for means and  stdev"

######## iteration 1 ###########
2 classes, 100.00% points stable
class distribution
       2161          7

########## final results #############
1 classes (convergence=100.0%)

class separability matrix


         1

  1      0


class means/stddev for each band


class 1 (2161)
  means    0.00   0.00   0.00
  stddev   0.00   0.00   0.00



#################### CLASSES ####################

1 classes, 100.00% points stable

######## CLUSTER END (Mon Jun 16 15:12:59 2008) ########


I assume this is due to the very low range of values (0.0xxx) of the
input images.  Running r.rescale.eq to "stretch" the range of values
doesn't also help.
Any ideas on converting the radiance values to a range acceptable to
i.cluster and i.maxlik?

cheers,
maning

PS. Running i.landsat.rgb gives very good result to the output image
(less topographic effects) but this just changes the color rules and
not the actual values.


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