[GRASSLIST:4452] Temperature from LANDSAT-TM5 ch.6

[Hamish]

Hi,

I'm looking at some LANDSAT-TM5 data and I'd like to derive surface
temperature from channel 6 (thermal IR) as described in Neteler &
Mitasova (1st ed.) S9.4.3.

The results look all wrong though, I'm getting a range of -54 to +69 C.


Using the following formulae:

radiance = 1.238+(15.6-1.238)*tm6/255.0;
temp_kelvin = 1260.56 / log(607.76/radiance + 1);
temp_celsius = temp_kelvin - 273.15

we get:

tm6(0) = -69.7787 deg C
tm6(255) = 68.6640 deg C


Using d.histogram on the "tm24r_b6" 8bit GeoTIFF input raster, I see a
bimodal distribution with peaks at 75 (land) and 220 (ocean). That
translates to -6deg for the land and +57deg for the ocean...

is my satellite data wrong or is it the conversion formulae?


thanks,
Hamish