Impact driving: Prognosis of cumulative SEL and DTT

To represent a simplified case of a fleeing animal, it is assumed that the receptor moves radially away from the noise source at constant speed vf and starting at initial distance r0.

27 The SEL is numerically cumulated as the receiver moves away along the transect and receives new partial doses for each range step. The calculation is truncated in case the transect reaches shore (Section 4.3).

For the receptor at range ri [m] from the source, the sound exposure contribution at that range step is Ei [Pa²s]. For the full piling sequence, the cumulative SEL in dB re 1 µPa²s becomes:

𝐿𝐿_{𝐸𝐸,𝑐𝑐𝑐𝑐𝑚𝑚}= log₁₀^{𝐸𝐸𝑐𝑐𝑐𝑐𝑐𝑐}_𝐸𝐸

0 = 10∙log₁₀^{∑ 𝐸𝐸}_𝐸𝐸^𝑖𝑖

0 𝑑𝑑𝑑𝑑

Here, E0=1 µPa²s is the reference value for sound exposure.

At time ti after piling onset, the receptor is at range ri=r0+vf⋅ti.

For the Reference Case of Section 4.1.1, the Prognosis is carried out assuming r0 = 200 m.

For the Planned Construction Case and Specific ADD Case of Section 4.1.1, an iterative procedure shall be applied for determining LE,cum as a function of r0. This relation is then

evaluated for Distance-To-Threshold (DTT) of the acoustic criteria as described in Section 4.1.1.

The process is illustrated schematically in Figure 3.

For both the Planned Construction case and Specific ADD case, DTT must similarly be

determined for behavioural disturbance. The procedure is done for SPL125 ms, which is estimated from SELss, see Section 1.2

In the following, all metrics shall be calculated per 1/3-octave frequency band with appropriate frequency weighting according to Section 1.15. Hence, in SELcum,xx the subscript xx refers to the auditory weightings LF, HF, VHF, or PCW in the following.

Figure 3: Overview flow diagram showing iterative procedure for Distance-To-Threshold.

28

SEL

calculation based on N

curve fit

Due to issues related to acoustic interference patterns at low frequencies, the curve fit method of this section is not suited for the LF auditory group.

As mentioned in Section 4.5.4.1, a measurement-based transmission loss ∆LTL [dB] may be curve fitted to an expression of the type ∆LTL=XTL⋅Log10(r)+ATL⋅r.

In the following it assumed that an analogous fit has been obtained for propagation loss NPL,E

[dB re 1 m²]:

𝑁𝑁_{𝑃𝑃𝑃𝑃,𝐸𝐸}=𝑋𝑋 ∙log₁₀(𝑟𝑟) +𝐴𝐴 ∙ 𝑟𝑟 𝑑𝑑𝑑𝑑

Here, X [-] is a positive constant, and A [m^-1] is a positive or negative constant.

Assuming the noise to be emitted from an equivalent point source of sound exposure source level LS,E [dB re 1 µPa²m²s], the received single-strike SEL at any range r [m] is calculated as LS,E minus NPL,E(r).

Let the unweighted source level LS,E [dB re 1 µPa²m²s] corresponding to 100% impact hammer energy be:

𝐿𝐿_{𝑆𝑆,𝐸𝐸}= 10∙log₁₀^𝐸𝐸100%_𝐸𝐸

0 𝑑𝑑𝑑𝑑

The energy of the i’th strike out of a total of N strikes is related to the maximum energy by:

𝐸𝐸𝑖𝑖%= 𝑆𝑆𝑖𝑖

100% ∙ 𝐸𝐸^100%

Here, Si is the percentage of full hammer energy of the i’th strike, see also the hammer protocol example of Table 7.

By a receptor at distance ri [m] from the source, the sound exposure dose received from the i’th strike will depend on the hammer energy of the i’th strike as well as the propagation loss and thus be:

𝐸𝐸𝑖𝑖%= 𝑆𝑆𝑖𝑖

100% ∙ 𝐸𝐸⁰⋅₁₀^{𝑃𝑃𝑆𝑆,𝐸𝐸−𝑁𝑁}10^{𝑃𝑃𝑃𝑃,𝐸𝐸}

In this, the sound exposure-based propagation loss NPL,E is approximated as 𝑁𝑁𝑃𝑃𝑃𝑃,𝐸𝐸(𝑟𝑟_𝑖𝑖) =𝑋𝑋 ∙log10𝑟𝑟𝑖𝑖+𝐴𝐴 ∙ 𝑟𝑟𝑖𝑖=𝑋𝑋 ∙log10(𝑟𝑟0+𝑣𝑣𝑓𝑓∙ 𝑟𝑟𝑖𝑖) +𝐴𝐴 ∙(𝑟𝑟0+𝑣𝑣𝑓𝑓∙ 𝑡𝑡𝑖𝑖) 𝑑𝑑𝑑𝑑 The SELcum becomes:

𝐿𝐿_{𝐸𝐸,𝑐𝑐𝑐𝑐𝑚𝑚}= 10∙log₁₀∑ _100%^{𝑆𝑆𝑖𝑖} ∙10𝑃𝑃𝑆𝑆,𝐸𝐸−𝑋𝑋∙log10(𝑟𝑟0+𝑣𝑣𝑓𝑓∙𝑡𝑡𝑖𝑖)−𝐴𝐴∙(𝑟𝑟0+𝑣𝑣𝑓𝑓∙𝑡𝑡𝑖𝑖) 𝑁𝑁 10

𝑖𝑖=1 𝑑𝑑𝑑𝑑

29 All hammer strikes of the hammer protocol within a maximum of 24 hours shall be included in SELcum.

For values of fleeing speed vf, see Table 5.

If LS,E is prognosticated at several depths, the largest value must be used for the calculation of SELcum.

After calculating the unweighted SELcum as described above for each 1/3-octave band, the relevant auditory frequency weightings of Section 1.15 are applied and a weighted broadband value SELcum,xx is calculated.

SEL

approach based on fine-resolution sound field

If the sound field of SELss is provided in a vertical plane 2D grid along a transect, SELcum may be calculated directly from this without use of curve fitting. It is assumed that SELss is available for all relevant 1/3-octave bands in every grid-point.

Often, the spatial resolution of a numerical model is in the order of metres or decimeters. This fine-resolution grid may, as follows, be used analogously to the curve-fit based approach of Section 4.7.1, with the introduction of Max-Over-Depth, MOD (see definition in Section 1.9).

Preferably, all available grid-points may be used for SELcum. Alternatively, a smaller set of evaluation points using this approach shall be separated by maximum 20 m in the horizontal plane. Similarly, in vertical direction the points distributed across the water column shall be separated by maximum 1 m.

• First, all 1/3-octave band values of all evaluation points (i.e. selected grid-points as mentioned above) are frequency weighted according to Section 1.15. For each point, the broadband frequency weighted SELss,xx is calculated.

• Next, the depth dependence is removed by evaluating MOD for each range step throughout the length of the transect.

The animal receptor is assumed to flee at constant speed vf [m/s]. At time ti [s] corresponding to the i’th hammer strike, the receiver is at distance 𝑟𝑟𝑖𝑖=𝑟𝑟0+𝑣𝑣𝑓𝑓∙ 𝑡𝑡𝑖𝑖 [m] from the source. For values of fleeing speed vf, see Table 5.

After these preceding steps, SELcum,xx is evaluated over the entire piling sequence as:

𝐿𝐿𝐸𝐸,𝑐𝑐𝑐𝑐𝑚𝑚,𝑥𝑥𝑥𝑥 = 10∙log₁₀�10^{SEL𝑠𝑠𝑠𝑠,𝑥𝑥𝑥𝑥10(𝑟𝑟𝑖𝑖)}

𝑁𝑁 𝑖𝑖=1

𝑑𝑑𝑑𝑑

30 Note that until this point, SELss,xx is defined for discrete values of r, and one must provide a scheme for evaluating SELss,xx for the required values of ri, e.g. by linear interpolation. The applied method must be described.

All hammer strikes of the hammer protocol within a maximum of 24 hours shall be included in SELcum.