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Walddämpfung (ISO-9613)

Simple method

For ISO9613-calculations, the "simple" method is based on the one originally specified in [ISO9613]. This method is also presented as the "simplified method" in [ISO9613:2024], A.2.2.

❑  Anmerkungen:
  • The here implemented extension allows for the specification of the attenuation coefficient at 500Hz; a value of 0.05dB/m leads to the attenuation specified in the original method (which is intended to model a dense forest).

  • For spectral sources, the provided coefficient is used for 500Hz.

  • In this method, the "through-forest-path-length" (length of the portion of the 5km-radius curved path that lies within the forest, excluding the portion above the trees) is used to obtain the total attenuation (see image); note however that the standard limits this length (hard bound at 200m). For details, see [ISO-9613-2].

Method based on forestal parameters ("detailed method")

The "detailed" method [≥SLIP'25] is introduced in the 2nd edition of the ISO9613 standard, section A.2.3 [ISO-9613-2:2024]. It uses forestal parameters (stem diameter, basal area, standing stock, horizontal structuring and low-height foliage) to estimate a spectral attenuation coefficient.

❑  Anmerkungen:
  • For nonspectral sources, the attenuation for 500Hz is used.

  • The ISO9613-standard provides typical parameter values for light, normal and dense forests; these are displayed in the following table.

    forestal parameter light forestnormal forestdense forest
    stem diameter [cm] 10 25 40
    basal area [m2/ha] 15 32 50
    standing stock [m3/ha] 100 250 400
    horizontal structuring [class]none (0) minor (1) major (2)
    low height foliage [class] none (0) minor (1) major (2)

  • When using this method, the "through-forest-path" usually (central case) consists of two straight segments that rise (relatively to the ground) from the source and from the receiver, respectively; see image. [For this documentation, mentioning this central case might be sufficient, but note that the present implementation covers all possible cases.] See also [ISO-9613-2:2024].

See also