[GRASS-user] Estimating Albedo from Landsat

Hamish hamish_b at yahoo.com
Tue Sep 14 18:48:42 EDT 2010

Nikos wrote:
> ... I realised that I don't really have the "correct" metadata file for 
> the scene I was given. The "meta" file available at Glovis is not really
> the complete set of meta-information (is my guess -- missing
> "sat_zenith=" value for example).

fwiw with Landsat-7 downloads from GloVis I get files like
L7*_MTL.txt which works with the i.landsat.toar metfile= option, it
includes SUN_ELEVATION and SUN_AZIMUTH but nothing obvious about zenith
that I can see.

looking in the source code, landsat_met.c (which parses the metadata file)
isn't looking for satellite zenith- it only comes from the command line,
and in landsat.c it seems that only the DOS2b, DOS3, and DOS4 correction
methods actually use it. So for uncorrected method (which I guess is the
appropriate one if the task is cloud detection??) that variable doesn't

> the output values (even if the sat_zenith value I used is
> non-sense) seem to be as expected for radiance/reflectance values


> (e.g. band 1, 
> min=-0.00308741863579021, max=0.39202091888652) .

I think this already got answered a couple of days ago, but is the
reflectance on a scale from 0.0-1.0 (0-100%)?

and what are the W/m^2-like units for radiance used for the output maps?

> Is the following the problem (you expect-ed)? I see strange
> characters, e.g.:
> -------------------
>  BAND 1  (code 1)
>    calibrated digital number (DN): 1.0 to 255.0
>    calibration constants (L): -1.520 to 193.000
>    at-sensor radiance = 0.76583 � DN + -2.28583
>    mean solar exoatmospheric irradiance (ESUN): 1983.000
>    at-sensor reflectance = radiance / 492.32067
> -------------------
>  BAND 2  (code 2)
>    calibrated digital number (DN): 1.0 to 255.0
>    calibration constants (L): -2.840 to 365.000
>    at-sensor radiance = 1.44819 � DN + -4.28819
>    mean solar exoatmospheric irradiance (ESUN): 1796.000
>    at-sensor reflectance = radiance / 445.89406

no, that is something else, it's a non-ASCII char in the fprintf()
string. Maybe it will show up in the email: it's the dot multiplier "·".
for me in "less main.c" it shows up as <B7>, in nedit and vi I see the dot.
I guess that should be %c + the code for it, or just "*" ?
.. displaying it will be terminal and locale dependent ..

> In my last test(s) no segfault occured...


> with or without "-v" !??

both should work.

> Even though "nice words" are inexpensive,

I don't think enough people really appreciate that cost/benefit ..

> I still think they are important (when they are honest). From my side,
> I just need some timing to contribute back - 
> all seems to go wrong currently :-p

best of luck & enjoy your time,


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