[GRASSLIST:7638] Convert DN's to reflection and r.patch

[Rahul Chopra]

Hi all,
I was wondering if I could get some assistance with respect to the
conversion of digital numbers to reflectance values for Landsat 5 TM.

My study area is encompassed by 9 scenes.

I first converted DN's to radiance for each band of the 9 scenes using:
 r.mapcalc "bandn_rad = 1.0 * (bandn * GAINn) + BIASn))"

I then converted the radiance values are at-the-top-of-the atmosphere to
measures of reflectance using
rhop =1.0* (pi * L * d2)/(ESUN * cos(thetas))
where L is the measured TOA radiance, d is the earth-sun distance in
astronomical units, and thetas is the solar zenith angle

However, when I use r.patch to patch files for a particular band, the output
map looks fragmented and discontinuous and not seamless. That is each scene
appears separated from the others.

Could it be that I need to convert the raster maps from floating point
values to integers? Or might it be that I need to play around with the null
values?

Any help would be supremely appreciated.
Thanks
Rahul