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18-Jan-2022   
Path: RAMI-IV : EXPERIMENTS : ACTUAL CANOPIES : OFENPASS WINTER PINESTAND : Local uncollided transmission at lower boundary for direct illumination from finitesized sun
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Local uncollided transmission at lower boundary for direct illumination from finite-sized sun: ftran_dir_loc

This is the transmission of light originating within the solar disc that traverses the canopy unhindered down to some reference x,y location (within the canopy scene) at a height level of 0.5 m above the background surface (it is thus similar to the direct transmission estimates of the TRAC instrument, for example). Three different transects of such direct transmissions are to be generated. To account for the physical size of the solar disc all incident directions that lie within 0.25 degree of the solar illumination direction are to be included in these local direct transmission estimates. Furthermore the flux density of the radiation is to be assumed uniform 1) across the solar disc and 2) across the top-of-canopy level of the RAMI scene of interest. The ftran_dir_loc measurement applies to all RAMI scenes that are at least 1 hectare in area (i.e., HOMOGENEOUS ABSTRACT canopies are thus excluded). More specifically, ftran_dir_loc prescribes three different transects located at a height of 0.5 metres within the canopy scene and composed of 1201 local direct transmission measurements carried out at 5 cm interval. In the hypothetical case that a given local transmission measurement point along the transect is actually situated within a tree trunk then obviously the resulting transmission is 0. The location of the three transects is as follows:
  1. RAMI scenes that have the origin of the coordinate system in the lower left corner of the scene:
    • Transect A: from x,y location 20,80 to 80,80 in intervals of 0.05 m
    • Transect B: from x,y location 20,50 to 80,50 in intervals of 0.05 m
    • Transect C: from x,y location 50,20 to 50,80 in intervals of 0.05 m
  2. RAMI scenes that have the origin of the coordinate system in the center of the scene:
    • Transect A: from x,y location −30,30 to 30,30 in intervals of 0.05 m
    • Transect B: from x,y location −30,0 to 30,0 in intervals of 0.05 m
    • Transect C: from x,y location 0,−30 to 0,30 in intervals of 0.05 m

The following graphics provide an overview of the concept of this measurements as well as the labelling of the various transects:

Within RAMI-IV this measurement applies only to a selection of canopy scenes:

ftran_dir_loc file-naming convention:

Since ftran_dir_loc measurements are independent of wavelength, and in order to specify the transect location (A,B,C) within the filename itself, the RAMI file-naming convention will have to be adapted. Therefore, please modify the RED, NIR and B** spectral band identifiers into two zeros followed by the letter indicating the location of the transect (e.g., 00A, 00B or 00C) in the measurement filename. This naming strategies then results in the following filenames, for example, ftran_dir_loc_raytran-HET07_JPS_SUM_00C_36.mes for a ftran_dir_loc measurement along transect C in the Jaervselja pine stand and ftran_dir_loc_raytran-HET14_WCO_090_00A_50.mes for a ftran_dir_loc measurement along transect A in the Wellington citrus orchard if the sun is located at a SZA=50 and has an SAA of 90 degrees. Similarly, one should use ftran_dir_loc_raytran-HET10_DIS_UNI_00B_20.mes for the ftran_dir_loc measurement applied to transect B in the heterogeneous abstract canopy HET10_DIS_UNI with illumination conditions having an SZA of 20 degrees.

    Formatting of measurement-file content:

    Header line content # rows in file (# of local transmission estimates) # columns in file height of transmission measurements [m]
    Header line format integer integer real
    Body lines content X coordinate of local transmission estimate [m] Y coordinate of local transmission estimate [m] ftran_dir_loc
    Body lines format real real real

    where

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

    The order in which the transmission values are to be reported in transects A and B is by starting with from the smallest X coordinate value and going towards the largest X coordinate value. For transect C one starts with the smallest Y coordinate value and moves towards the largest Y coordinate value.

    Example output: Transect A in the case of a RAMI scene having the origin of the coordinate system near the center of the scene.

    1201 3 0.500000 0.050000
         -30.000000      30.000000      0.668422
         -29.950000      30.000000      0.192887
         -29.900000      30.000000      0.068017
         -29.850000      30.000000      0.122837
         -29.800000      30.000000      0.284787
         -29.750000      30.000000      0.172861
         -29.700000      30.000000      0.107715
         -29.650000      30.000000      0.897916
         -29.600000      30.000000      0.342299
         -29.550000      30.000000      0.415999
         -29.500000      30.000000      0.414099
         -29.450000      30.000000      0.411679
    ....
    

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