Markus Neteler wrote:
> Remember that you have to rescale these data first:
>
> https://lpdaac.usgs.gov/lpdaac/products/modis_products_table
> -> MOD09Q1 Terra
Surface Reflectance Bands 1–2
Tile 250m
8 Day
> https://lpdaac.usgs.gov/lpdaac/products/modis_products_table/surface_reflectance/8_day_l3_global_250m/v5/terra
> -> layers
>
> ... MULTIPLY BY SCALE FACTOR ...
Nikos wrote:
Yep, I know that. But why is it wrong to just use them as they are?
FWIW, the MODIS/Aqua Chlorophyll-a product requires more than simple
linear rescaling:
r.mapcalc "${map}.chlor_A = 10^(($Slope * $map) + $Intercept)"
http://grass.osgeo.org/wiki/MODIS#Processing_2
so you may need to take care if working directly with raw 0-65535 data.
Hamish