In a reply Jim W. commented
Yes, GRAASS can be used to do volumetric calculations. There is no
straightforward program, but the following outline will start you
in the right direction:
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Maybe I'm missing something here but what about r.volume
r.volume GRASS Reference Manual r.volume
NAME
r.volume - Calculates the volume of data "clumps", and
(optionally) produces a GRASS site_lists file containing the
calculated centroids of these clumps.
(GRASS Raster Program)
???
w. Fredrick Limp
CAST
Fayetteville AR 72701 fred@kirk.uark.edu