In our vegetation BRDF model and its application studies

we developed an indirect measuring method named the Tree Computed Tomography （TCT） for gathering tree crown architecture parameters

which include the Leaf Angle Distribution （LAD）

Foliage Area Volume Density （FAVD）

and Leaf Area Index （LAI）.  With direct method in field

it is difficulty to measure this kinds of architecture parameters

especially for trees. The TCT algorithm combining both computed tomography theory and vegetation canopy gap probability model

makes the indirect method be possible in tree crown architecture measurement. To improve and validate the algorithm

the Tree Computed Tomography field data gathering System（TCTS） was designed for getting more reliable multiviewing points image set in field. Both coniferous and deciduous crowns were selected to do indirect and manual direct measurement to get crown architecture parameters for the validation.  To improve our TCT algorithm

the average skylight distribution during the multiviewing points data gathering is reconstructed

the LAD estimation is considered

and the trunk/branches information is taken into account of FAVD reconstruction. Comparing the reconstructed 3d FAVD and manual measurement data

the results show that the reconstructed FAVD fit the manual measurement data very well. Then these indirect measured crown architecture parameters and measured radiance of lighted crown had been used in our BRDF model studies. This paper presents the above approach and the validation results.