Underwater Noise Measurement Intercalibration Practices Experience

13

6-8 kHz for several instruments. Distinct peaks reflect the frequency response from
pontoon calibration.
The decreasing sensitivity of the BSH Sylence LP likely stems from its mounting
holder.
Overall, deviations are similar in magnitude but differ in spectral structure. As noted
2y Hayman et al. (2016), single-frequency pistonphone checks and broadband free-field
calibrations are not directly interchangeable but together help identify systematic,
frequency-dependent variations in sensitivity. Remaining deviations may reflect hardware
 design, mounting configuration, or open-water variability. Further workshops and
intercalibration exercises will be required to quantify these uncertainties more robustly.

Tank-Pontoon Comparison and Calibration Uncertainty

To evaluate the reproducibility of the calibration results, clip-level curves from the
tank and pontoon were compared for instruments measured at both sites (Fig. 5). The
comparison was restricted to the overlapping 2-10 kHz band, and the frequencydependent
 differences AL(f) = L_tank — L_pontoon were used to estimate the interfacılıty
 variability.

Pontoon - Tank [dB*

X
\

=»BSH Sylence
— AU ST600HF
— FOI ST300HF
— FO] Sylence
— TUT Sylence.

\

Cm
oO
Do
UM

2

nm

<A

mn,

B

3 ' —
2000

3000

4000

5000

6000 7000
Frequency [Hz]

—— 4
8000 9000 10000

Fig. 5 Difference of clip levels of pontoon and tank calibrations during the HELCOM calibration
workshop