Noise emitted by container terminals has become a critical issue due to conflicting motives; noise nuisance has to be limited whilst decreasing lay time and increasing cost pressure requires fast-as-possible container handling. The latter, in turn, usually results in higher noise levels due to high operating grade of the handling equipment and, sometimes, noisy lift-and-drop actions. Additionally, many modern ports, as a consequence of their expansion, tend to grow closer to residential areas, in Bremerhaven, as close as a few hundred metres. Last, but not least, the sensitivity to the noise issue has been growing in the public arena over the last years.
Against this background, essential questions arise: which of those, more than typically 1000 relevant emission sources with levels up to 120 dB(A), may have an impact on the noise nuisance at the immission site? What does this mean for day or night? How many potential wake-up incidents occur per night? In some cases, psychoacoustical aspects may not be disregarded, too, such as the historical character of the residential area and the dwellers’ attitude towards port activities. Finally, the most important question: how to reduce noise efficiently and promptly?
Measuring technology
At this point, a measuring and notification system is necessary. In the case of the new container terminal in Bremerhaven, such a system has been defined as mandatory in the plan approval order, following the dispute during the planning phase. This decision was based on the experience gained with the former monitoring system that had been established by ted GmbH, Bremerhaven, in the course of the previous realisation of a container terminal. That system, which had been in operation until 2011, could already help to ease the situation of the conflicting interests mentioned above. Another result observed in recent years was, that in spite of increasing container handling rates the noise immission near the residential area stayed rather constant. Regardless of the sound mitigation measures in detail, it became obvious that „what gets measured gets improved”. This result is supported by the expertise of the company ted GmbH gained over more than 15 years from working in the field of port-related noise, ranging from consulting service in the process of planning and authorisation to the evaluation of transportation equipment and technical measures for noise mitigation.
The experience in the area of long-term sound measurements in Bremerhaven since 1991 and in Hamburg since 1998 became part of the continuous development of measuring technology. But however, the former high-end measuring technique had to undergo a fundamental revision and development concerning the concept, the hardware and the software. As a consequence of the plan approval order, the port expansion required not only the extension of the measuring array (area?) to 1 square km, but also an automatic notification system, being capable to distinguish between sound incidences occuring on the new or the former container terminal, respectively. Once a peak pulse incident is measured at the immission site and it is correlated with sound data acquired in the terminal area, the corresponding terminal operator has to get immediate notice. However, in order to approach the problem of efficient noise reduction, the features formally defined are still not sufficient.
Noise mitigation in this context demands a precise knowledge of the type of noise sources, their location within the terminal area, the time and the duration of occurrence. At this point, comprehensive consulting activities had been delivered by ted GmbH, leading to the concept of a wide-ranging data acquisition with 14 microphones in combination with a fully-automated noise classification and localisation system. Its core consists of noise recognition algorithms, based on a patent held by ted GmbH and their partner, representing a unique selling point in sound monitoring systems. It is an essential precondition for separating the port-related sound signals from local noise near the microphone in the unattended long-term measurements; “non issue signals” are filtered out. The system is able to distinguish between different kinds of noise and can even determine the location of the corresponding sources on the terminal. The messages sent during the ongoing operation support the Operations Managers. Those activities or handling devices causing undesirable noise will be identified. This can result in further sound mitigation measures or relocation activities.
In respect to the technical realisation, the engineers and scientists had to meet different challenges. The transmission of low-voltage measuring data over long distances up to 1.8 km turned out to be unfeasible via shielded cable due to strong electromagnetic fields radiated by power lines installed nearby. Concurrently, a high quality of the data transmission is required for the spectral analysis and a wide dynamic range of more than 80 dB, which is essential for measuring the background noise level as well as the peak pulses. This has been fulfilled by implementing a fibre network of approximately 11 km including state-of-the-art audio transmitters, 24-bit signal processing components and measuring microphones meeting the Class 1 standard. The arrangement of the microphones has been carefully selected according to the distribution of emission on the terminal, also taking into consideration the port-related traffic by road and rail.
Fast data transmission
Furthermore, in order to precisely determine the place of emission, in simultaneous correlation with the measurement at the immission site, a fast data transmission across the terminal boundaries is necessary. This is achieved with a fast GHz wireless link between the central station and the immission measurement station. The complete monitoring system has been designed consistently for unattended operation ensuring low maintenance costs and a high degree of automation and operational availability over the year. Telecommunication equipment provides for full remote control of the monitoring system, data access and a complaint-recording system via telephone for the adjacent residents.
However, most of the know-how is located in the purpose-built software. Particularly, it includes the patent-registered automatic noise recognition and separation system, but also the noise localisation algorithms. The latter are based on the correlation of emission and immission sound data analysing incident levels and detected instants of time, in combination with a peak pulse analysis. If a peak pulse incident near the homes, which exceeds the maximum level, has been allocated to the operation of the terminal, the notification routine immediately sends an email or fax to the operational manager on duty of the respective terminal section. Information about the localisation of the noise is included in the message.
Additionally, an online display of measuring data has been developed, showing the current sound pressure level at the immission site and the most relevant meteorological data. This gives the worthwhile opportunity of evaluating the actual degree of noise nuisance over the internet. More detailed information can be made available for the terminal operators. A full data access as well as remote control and maintenance functions has been established, too. An almost fully automated report compilation and documentation complete the comprehensive function volume. Detailed recording of sound pressure levels, spectra, meteorological data and audio signals is a basic must in the context of sound monitoring.
The experiences gained from the noise monitoring system during the first weeks of field test are promising: the complex interaction between sophisticated hardware and software algorithms works, and, as a first step on the way to a more silent port, the awareness of the issue „noise” seems to have grown among the parties involved. In the end, sound monitoring is worth the effort in view of t
he close coexistence of ports and residential areas.