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Uncollided transmission at lower boundary level for direct illumination only: ftran_uc_dir

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.

Within RAMI-IV this measurement applies to all canopy scenes. However, 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 ftran_uc_dir_raytran-HET14_WCO_090_B00_20.mes for the Wellington citrus orchard illuminated at SZA=20 and SAA=90 degrees, respectively. In the case of the abstract canopies, for example, the experimental identifier HOM24_DIS_PLA_RED_20 should be changed into HOM24_DIS_PLA_B00_20 and ftran_uc_dir_raytran-HET10_DIS_UNI_B00_20.mes relates to the heterogeneous abstract canopy having the experimental identifier: HET10_DIS_UNI_20. 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.

Formatting of measurement-file content:

Content ftran_uc_dir standard deviation of ftran_uc_dir*
Format real real
*: if not available set to −1.000000.

A real is defined as having 6 digits after the decimal point, e.g., 1.000000.

Example output:

0.123456	-1.000000