> I recently decided to use i.composite to work with some TM imagery.  I
> have no idea what combinations of which bands will produce what results. 
> Any assistance would be appreciated.
> 
> ---
> tim


Well, the basic rundown on TM imagery goes something like this.

TM Spectral Bands:
1       blue (0.45-0.53 um)
        Recommended for use in combination with other bands because of low contrast
        and high sensitivity to haze.

2       green (0.52-0.60 um)
        Recommended for use in combination with other bands because of low contrast
        and high sensitivity to haze.

3       red (0.63-0.69 um)
        Best for showing roads and bare soils.  This band heightens the contrast between
        vegetated and non-vegetated areas.

4       near-infrared (0.76-0.90 um)
        Useful for biomass estimation. It also separates water bodies from vegetation. 
    	Not as effective as tm3 for identifying roads.

5       shortwave infrared (1.55-1.75 um)
        Best single overall band.  It shows roads, openings, bare soils, water 
        good contrast between different types of vegetation.  It also has excellent haze
        penetration.

6       thermal infrared (10.5-12.5 um)
        This band responds to thermal radiation emitted by the target.  Thermal IR is
        closely related to soil moisture and the height and temperature of the vegetation.
        Data are acquired at night to obtain maximum information. (note 80m res for
        this band only)

7       shortwave infrared (2.08-2.35 um)
        This band has greater haze penetration than tm5.  It is less useful than tm5 for
        interpreting vegetation cover, but has strong potential for soil analysis.

Colour Composits in BGR order:

234     Sensitive to green vegetation (portrayed as red), coniferous as distinctly darker
        red than deciduous forests.  Roads and water bodies are clear.

345     contains one band from each of the main reflective units (vis, nir, shortwave
        infra).  Green veg is green and the shortwave band shows stress and mortality.
        Roads are less evident as band 3 is blue.

347     similar to 345 but depicts burned areas better.

243     green veg is green but coniferous forests arenUt as clear as the 234 combo

354     appears more like a colour infrared photo

374     similar to 354

123     true colour, however because of high correlation of the 3 bands in visible this
        combo contains not much more info than contained in one band alone.

457     shows soil texture classes (clay, loam, sandy) by CCRS researchers.

247     one of the best for info pertaining to forestry.  good for operation scale mapping
        of recent harvest areas and road construction.

The source of this info is the Canadian Centre for Remote Sensing btw.  If you need any 
more help just email me directly.

///\\\///\\\///\\\////
Kevin Seel
Golder Associates Ltd.
Calgary, Alberta, Canada
seel@fsa.ca



