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Isotropic Bihemispherical Reflectance (White Sky Albedo): bhr_iso

The isotropic bi-hemispherical reflectance is defined as the albedo of a target that is illuminated in a spatially-uniform manner at the top-of-canopy level by an isotropic diffuse light source, i.e., the intensity of the incident radiation is independent of direction. Based on these illumination conditions, the bhr_iso can then be said to be equal to:

where the projected solid angle [sr] is given in terms of zenith (θ) and azimuth (ϕ) angle by:

Notice that within RAMI all incident and exiting radiation has to pass through a (virtual) planar reference surface of specified lateral dimension and elevation above the target, and oriented perpendicular to the underlying surface normal.

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

    Formatting of measurement-file content:

    Content isotropic bihemispherical reflectance standard deviation of bhr_iso estimate*
    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

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