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 hard- 
ware 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 frequency- 
dependent differences AL(f) = L_tank — L_pontoon were used to estimate the inter- 
facılıty 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