integration of tabulated data in spherical coordinates

[bonnefoy(at)obs.ujf-grenoble.fr (Nicolas Bonnefoy)]

Hi,

My experiment (a goniometer) is aimed at measuring the light reflected
by a surface for several geometric configurations; to describe the 
whole upper hemisphere, in spherical coordinates (radius, latitude,
longitude), the observation angle is in the range 0-90 degrees in
latitude, and 0-360 degrees in longitude. To determine the albedo of the
surface, I need to integrate these reflectance measurements over the
hemisphere.

First, I used Sph_Scat to perform a spherical gridding of my data with a
better angular resolution (5 degrees in latitude and longitude, instead
of the 10 degrees of the measurements).

But my problem is that I did not find any IDL routine that integrates
the volume formed by a surface defined by tabulated data (my
measurements) in spherical coordinates (radius, latitude, longitude).

Has anyone solved this problem before, or have any ideas on to do it?  

Thanks

Nicolas