Abstract
This report provides a summary of underwater noise measurements conducted in 2013 and 2014. The key findings based on the preliminary analysis of the collected data are as follows:
1. Sea noise measurements made at the two sites, GEMINI 1, 40 km west from the Gemini windpark, and GEMINI 8, between the two halves of the Gemini windpark, provide information on ambient noise in the area. Anthropogenic sources of underwater noise, in particular, shipping traffic, a geotechnical survey, and pile driving sound, were the major contributors to the noise environment in the area.
2. The underwater noise environment at GEMINI 1 (more easterly of the two positions) is more heavily dominated by shipping noise, mechanical noise − presumably associated with trawling. Shipping noise was highly variable in intensity and comprised noises from both near and distant vessels. Even though pile driving noise from construction of windparks in adjacent German waters was recorded at higher levels at station GEMINI 8, periods of intense noise from pile driving were evident in recordings from both positions. Additional information is required on piling locations and times from the operators for a more comprehensive analysis and more definite conclusion on the contribution made by these operations to ambient noise.
3. Sounds of biological origin were rarely evident in the datasets. This can partly be attributed to the frequency range of these recordings, which was limited to 24 kHz to compensate for energy and data storage demands thus eliminating sounds produced by harbour porpoises. Fish sounds, such as choruses produced by fish in tropical regions, were not expected and have not been detected in any of the recordings.
4. Noise recorded at both stations was up to 20 dB higher in certain frequency bands during periods when there was man-made noise than during periods when man-made noise was absent. On average, over the entire period, there was approximately a 5-10 dB difference between the two noise logger stations over most of the frequency band. In 2013, noise levels from GEMINI 1 were, on average, higher than those from GEMINI 8 while the recordings from 2014 provide a reverse result.
5. Several underwater explosions were detected in the recordings from both stations. These acoustic events have the potential to adversely affect marine animals.
6. This report provides a description of back-ground noise (a base-line), both anthropogenic and natural, against which noise produced during construction and operation of the windpark can be compared. The report is largely descriptive of the types of noise present prior to construction of Gemini windpark. More detailed analysis and interpretation of potential impacts can be conducted on obtaining noise profiles during construction and operation.