Underwater Noise Measurement Intercalibration Practices Experience 
15 
magnitudes and frequency dependence of the combined uncertainties are in line with 
expectations and confirm that results from both facilities are within a reasonable range. 
Rig Designs 
In addition to the calibration exercises, participants exchanged experiences on rig 
design and deployment practice. The discussion highlighted that most national 
programs rely on variations of the same basic concept: sensors mounted on a single 
vertical line, typically positioned a few meters above the seabed, with buoyancy and 
weights balanced to ensure stability (HELCOM 2022). Reliable releasers were 
Fig. 7 Diagram of an 
example inline deployment 
with a porpoise detector (C/F- 
POD) and an audio data 
‚ogger, with a built-in 
hydrophone (left) and with a 
ıydrophone extended away 
from the audio data logger 
(right). (Diagram credit: 
Aarhus University (left) and 
FOI (right)) 
Satellite Transmitter 
L 
Floatation 
win 
) 11m apart 
[-ı 
Audio data 
Logger* 
ım apart 
Porpoise Detector 
Releaser 
Stone Bags