Uncollided transmission at lower boundary level for direct illumination only
This is the fraction of the incident direct radiation - passing through a planar reference surface of specified lateral dimension and elevation above the target, and oriented perpendicular to the underlying surface normal - that is transmitted down to the level of the background (at z = ∼ 0) without undergoing any collisions within the canopy volume that it traverses. ftran_uc_dir does not include contributions from isotropically diffuse illumination sources (should they be prescribed in the illumination conditions of a given RAMI experiment). ftran_uc_dir is thus the magnitude of the un-collided direct-only radiation impinging on the background surface normalised by the magnitude of the incident direct-only radiation at the top of the canopy (entering through the reference area).
ftran_uc_dir = transmission due to direct incident radiation that has no scattering interactions with the canopy.
|standard deviation of ftran_uc_dir estimate*
*: if available, otherwise set to −1.000000.
Since ftran_uc_dir measurements are independent of wavelength they will have to be carried out only once for a given canopy scene and illumination condition. Therefore please exchange the RED or NIR or B** spectral band identifiers by B00 in the names of the ftran_uc_dir measurement files. This filenaming strategies then results in the following filenames, for example, ftran_uc_dir_raytran-HET07_JPS_SUM_B00_36.mes for the Jaervselja pine stand and HET14_WCO_090_B00_Z20A090-ftran_uc_dir_raytran.mes for the Wellington citrus orchard illuminated at $\theta_i$=20 and $\phi_i$=90 degrees, respectively.
In the case of the abstract canopies, for example, the experimental identifier HOM24_DIS_PLA_RED_Z20A000 should be changed into HOM24_DIS_PLA_B00_Z20A000 and HOM24_DIS_PLA_B00_Z20A000-ftran_uc_dir_raytran.mes relates to the heterogeneous abstract canopy having the experimental identifier: HET10_DIS_UNI_Z20A000. Obviously in the case of the anisotropic background test cases, the ftran_uc_dir measurements will be the same irrespective of whether the RPV parameters relate to soil, vegetation or snow.