[GRASS-user] Negative raster values from i.landsat.dehaze

[Markus Neteler]

Hi James,

On Thu, May 3, 2012 at 10:05 PM, James Travers <traversjames at yahoo.ie> wrote:
>
> Ok, I have done a bit more digging and found r.univar for the stats problem
> - don't know how I missed that one!

glad you found it. If you see any potential to improve the documentation,
please make suggestions.

> On the atmospheric correction I have ditched i.landsat.dehaze in favour of
> the presumed higher accuracy of i.atcorr.

i.landsat.dehaze is "just" a simple statistical approach.

> So, with this I have created a
> control file with the relevant values for e.g. Band-3:
>
> #--------- start of control file -----
> 8                            - geometrical conditions=Landsat ETM+
> 3 24 08.020 35.400 32.680    - month day hh.ddd longitude latitude ("hh.ddd" is in GMT decimal hours)
> 2                            - atmospheric mode=midlatitude summer
> 2                            - aerosols model=maritime
> 50                           - visibility [km] (aerosol model concentration)
> -0.080                       - mean target elevation above sea level [km]
> -1000                        - sensor on board a satellite
> 63                           - 3rd band of ETM+ Landsat 7
> #--------- end of control file -------
> When I then run i.atcorr:
>
> $ i.atcorr -r -a iimg=R3 icnd=icnd3.txt oimg=C3D
> ERROR: Raster map <dem_float> not found

I just tried with the example of the manual page in the North Carolina
sample dataset and it worked ok. But: don't put the comment lines
into the control file! I fell into this trap in the beginning and i.atcorr
offered weird error messages.

> The error is refers to the default altitude raster-map, but the command help
> specifies that the ialt argument is optional and I don't have a DEM for the
> area.  Any ideas what is going on?

I suspect that you have the two comment lines in the file which
unfortunately confuse i.atcorr.

Markus