TECHNOLOGY ADVANCES IN REMOTE NOISE MONITORING NOISE-CON PORTLAND, OREGON JULY Greg Bracci. Brüel & Kjær EMS

Transcription

1 TECHNOLOGY ADVANCES IN REMOTE NOISE MONITORING NOISE-CON PORTLAND, OREGON JULY Greg Bracci Brüel & Kjær EMS 5189 Lake Creek Court Frisco, TX USA greg.bracci@bksv.com Phil Stollery Brüel and Kjær EMS 34 Cumberland Ave Fixby Huddersfield HD2 2JJ phil.stollery@bksv.com Brüel & Kjær EMS

2 TABLE OF CONTENTS 1. Abstract Introduction The Challenges with remote monitoring Instrumentation develpoments Automatic Source detection Monitoring functionality The Approach to Monitoring Conclusion References...11 Brüel & Kjær EMS Page i

3 1. ABSTRACT Long term monitoring of noise from airports, industrial facilities and construction projects has been well established over many years. The systems monitor noise levels at various points around the facility, feed the data back to a central system where data can be summarized and any breaches in compliance criteria are reported. These systems are passive by nature; they simply report what happened giving little opportunity to do anything to prevent breaches in the first place. Should breaches occur, attendance at the site is typically necessary to investigate before advice on mitigation can be given to prevent future breaches of compliance. Technology advances in how data is captured, what data is captured and how it is accessed now means that in a large number of cases investigation can be achieved remotely without the need for site visits. This makes the process more efficient, lower cost, and much more immediate. Technology can now deliver results in real time that can help to prevent breaches occurring in the first place. This paper outlines the technology advances and suggests how they will help to change the way noise consultants can deliver more monitoring services over a wider geographical area with fewer staff whilst simultaneously providing a better quality result. 2. INTRODUCTION Around the world, Brüel & Kjær has witnessed increasing interest and investment in noise monitoring around industrial facilities, mines, large construction sites and major entertainment event sites as the operators of these facilities invest proactively in the maintenance of what we call environmental capacity the extent to which a community will allow a facility to impact on the noise climate around the site. Effective management of environmental capacity requires continuous monitoring to ensure agreed levels are complied with and to ensure that facilities are able to demonstrate compliance at all times. With the important time periods for nuisance at night time and weekends lying outside standard working hours, automatic unattended noise monitoring is critical to providing a viable solution. Brüel & Kjær EMS Page 1

4 Figure 1 IT Advances have driven improvements in almost every area of remote monitoring Advances in information technology have helped to improve instrumentation and find ways to automatically detect noise sources; both of which have enabled increased functionality. Developments have also helped to change the entire approach to noise monitoring by delivering a range of benefits making continuous monitoring more feasible and more desirable. 3. THE CHALLENGES WITH REMOTE MONITORING Long term unattended monitoring presents a variety of challenges. The ultimate goal is to replace the function of a person on site equipped with a sound level meter with a technology solution that is just as effective, lower cost, more scalable and much less tedious for the operator. Aiming for this goal poses a number of challenges including, power, communications, instrument reliability and calibration etc. Most importantly, and perhaps not immediately apparent, is the need to identify noise sources. This is essential not just to determine facility responsibility for the noise, but also to support and inform mitigation actions. During an attended survey, source identification is instinctively achieved by the operator observing the environment and noting down source descriptions. In recent years advances in information technology have enabled noise level information to be supplemented with other data to automate source identification to a degree and to enable remote investigation. Brüel & Kjær EMS Page 2

5 4. INSTRUMENTATION DEVELPOMENTS Field based permanent noise monitoring has been established since the 1970 s. Originally comprising of analogue based noise instruments coupled with a digital data logger, these devices stored simple broadband noise metrics at regular intervals. Frequent visits to the site were necessary to collect data until analogue telephone lines were used to automatically capture data from the data loggers. The early 1990 s saw the first fully digital noise monitoring terminals. These incorporated modems for automatic data capture over analogue telephone lines and contained significant processing capabilities on site. The slow data transmission rates effectively limited the amount of data that could be transmitted across the line. Key uses for the on board processor was to analyze both the time data into periodic (typically hourly) measurements and noise events for any significant deviations from background levels. This effectively cut down the amount of data that needed to be transmitted to be able to describe the noise climate on site. This was beneficial but being remote from the site meant that there was a thirst for more data to be recorded and transmitted. Fortunately, technology gradually progressed to enable more local processing, more local storage and faster communication. Moore s law 1 has consistently predicted that the number of transistors on a given size of integrated circuit will double every two years. Amazingly this has held true since it was first hypothesized in 1965 and effectively means that processing power and storage capacity has increased at the same rate. In airports, the Effective Perceived Noise Level metric was widespread in certification and required capturing 1/3 rd octave band frequency levels every ½ second. EPNL became a standard addition to airport noise monitoring in the mid 1990 s closely followed by 1/3 rd octaves themselves, which of course immediately multiplied communication rates and storage capacities by a factor of 33. By the millennium permanent noise monitors were now capable of recording and storing large amounts of sampled audio data giving extreme flexibility as this data could be reanalyzed. Audio data rarely needs to be post processed in long Brüel & Figure Kjær EMS 2 A Directional noise monitor and resulting Page polar 3 noise plot

6 term monitoring as it is usually known beforehand what metrics are required; the main purpose of audio recording is for audio replay to aid source recognition. Since the introduction of audio recording, instrumentation has largely stayed the same in terms of what it can measure. For particular applications we have seen simultaneous time and frequency weightings but for the most part equipment delivers the noise metrics it did 10 years ago. Instead instrumentation has developed to provide additional monitoring capabilities to help support the noise information being recorded. Weather sensors are common place to ensure that when weather conditions are not suitable for accurate noise monitoring, those measurements are not considered for compliance monitoring. Initially including wind speed and direction, a more complete picture of the monitoring climate can be gained by also considering temperature, pressure, humidity and rainfall. All the aforementioned parameters would typically be recorded by the operator of a sound level meter prior to making an attended measurement. When a noise disturbance is heard in the community an operator making an attended measurement will observe the environment to capture additional information to help identify the noise source. This will include listening to the noise, noting which direction it came from, noting down tonality and other characteristics, and checking visually what operations are in progress. In unattended monitoring the need is the same, with the limitation that the operator is not present at the site or possibly at the time of the disturbance. We can now capture additional information to replicate these functions remotely including audio capture for later replay by the remote operator and video capture to view activities around the noise monitoring location during the disturbance. Not only do these help to identify sources, but they may be retained alongside noise levels to provide evidence should the facility s noise compliance be challenged. In complex multi source environments noting the directionality of noise is an important aspect. Noise rarely exists solely from the source that is being monitored and noise from other sources needs to be identified as such and removed from the assessment. It is unfair for a factory to be penalized with a compliance breach resulting from an aircraft overhead. Again the sound level meter operator on site has an advantage in being able to determine the direction of the noise. Now this capability is available in permanent noise monitors by using multiple microphones and automatic cross correlation processing to determine the direction of the noise level. Now, when monitoring an industrial facility for example, systems can automatically reject noise from other sources away from the plant. This is particularly important as compliance levels get lower and monitoring takes place further away from the source where contamination from general community noise is highly likely. Brüel & Kjær EMS Page 4

7 Advances in information technology have been able to support developments in instrumentation but it has not all been positive. The advances have also brought an additional challenge in terms of power consumption. Whilst digital instrumentation brings greater accuracy, reliability, functionality and usability it is at the expense of greater power consumption. Digital equipment consumes power orders of magnitude greater than older analogue equipment and power consumption is a key constraint to remote monitoring. High density batteries and low power digital signal processors have been developed for the smart phone market but acoustic instrumentation is somewhat different. The requirements for high precision audio capture and high speed processing over a very wide dynamic range means that today s digital sound level meters have limited battery life. Furthermore, smart phones can be placed into a low power standby mode that is received only when not being used. This isn t possible with noise monitors as they must operate continuously. You can have large battery banks to power noise monitors but this can rapidly become unworkable particularly if monitoring equipment frequently needs to be relocated. In many areas power problems may be alleviated with solar panels coupled with batteries providing continuous power year round but in high latitude areas solar becomes a greater challenge. For permanent sites, fuel cells can be a solution but these are expensive and will still require a site visit every 4 weeks to replenish fuel stocks. Figure 3 Solar and Wind power provide viable alternatives to ground power 5. AUTOMATIC SOURCE DETECTION Understanding which noise levels are the ones you are interested in and which should be ignored is critical to getting an accurate assessment of the noise from the facility of interest. We have seen how advances in instrumentation have enabled collection of data to facilitate source detection remote from site, however simply replicating the presence on site to a remote position whilst more palatable in inclement weather doesn t do anything to address the tedious nature of monitoring. Repeatable signal processing plays an enabling role making monitoring systems more effective than attended site monitoring and a lot more scalable and efficient. Outside of the defence industries, possibly most work in the area of source detection has been done for airport noise monitoring systems. In the early days of such systems this was achieved by looking at noise levels for significant deviations from the background. If the level was increased significantly for long enough duration it was deemed to be an aircraft. This was Brüel & Kjær EMS Page 5

8 successful only in filtering out noise from shorter time duration sources such as road traffic. Systems became more sophisticated by fusing the noise data with other sources of information such as radar systems to determine where aircraft are flying. Thus noise could only be classified as aircraft noise if an aircraft was within range of the measurement site at the time of the noise event. Further data fusion with aircraft type, operation type and expected noise level before linking with a noise event means these systems are capable of a high degree of aircraft noise correlation automatically typically with over 98% of all noise events correctly identified. Particularly where there is a lot of other noise, other attributes of the noise such as its spectral content can be useful information. Looking at the spectral content is very effective in identifying wind induced noise. High wind speeds can invalidate outdoor noise measurements, which is quite often the case at airports. However, as more and more airports are required to monitor further away from the airfield site, sometimes over 10km away and where aircraft are above 6,000 ft, community based noise is often significantly louder than that from aircraft. Detecting when aircraft noise is heard becomes more and more difficult. This has led to another level of sophistication in aircraft noise detection based on neural networks and other sophisticated processing. These networks learn the characteristics of aircraft noise and then use this information to pick out when aircraft noise is dominant. Such networks are in use in a few airports and can even separate out jets, turbo props and helicopters. Detection of the source of noise is one thing but what if the noise source you want to measure is quieter than the sources contaminating it? Using standard measuring techniques you can only measure the overall ambient noise level and you lose the ability to determine the level of the source you are interested in. Directional noise monitoring mentioned earlier can help here too. As well as determining the direction of levels the same processing is able to determine noise levels up to 10 db below the overall ambient noise level. Brüel & Kjær EMS Page 6

9 Figure 4 Monitoring noise below ambient levels Figure 4 is a trace from directional noise monitoring at a mine site for one day. The mine activity is in the selected direction. The black line is the noise compliance line which should not be exceeded. Note that the overall noise level (green line) is well above compliance from 06:00 to 18:00. Reviewing noise from the mine activity (red line) we can see a brief non compliance at point A. The source location and measurement reveals the detail of the mine activity beneath the overall noise level. Point B is where rock crushing activity starts, which doesn t have a visible effect on the overall noise level. After a short break it commences again at point C this time exceeding the define noise threshold. Measuring noise with standard equipment would show non compliance continuously throughout the day and fail to show the impact specific to the mine operation going on beneath the other sources. 6. MONITORING FUNCTIONALITY Once you have captured data and processed it, what you do with the data has also changed. In this case technology advances are not the driver for change they are an enabler. The drivers come from legislation, regulators and the community that are impacted by the noise. Noise monitoring systems are primarily utilized to monitor compliance where they routinely produce summary noise reports showing the monitoring levels against agreed limit level to show compliance. This is a purely reactive approach to noise. Advances in communication technology have enabled a valuable change in the way monitoring systems can be used. Data is now available in real time and can be monitored from anywhere. Should noise approach a threshold levels alerts can be generated to operating staff signaling them to cease and change site activities. This turns a monitoring system into a management system enabling operators to do something proactive rather than limiting themselves to reactive reporting of compliance. Real time noise management actually enables you to make their business quieter and by using Brüel & Kjær EMS Page 7

10 predictive alerting systems will now tell you, for example, that unless you reduce noise levels you will exceed your limit in 15 minutes; giving operators a clear opportunity to avoid breaches of compliance benefiting businesses, regulators and communities alike. In the last 20 years, IT storage and processing capacities have increased by several orders of magnitude. It used to be necessary to archive or destroy data older than 12 months whereas now it is practical to keep data from long term monitoring programs always accessible. The increased processing capabilities can work on this data to provide long term summaries and trends which can be very useful in managing noise issues for the future. Looking at longer term trends reduces the effect of short term changes to operating conditions, weather conditions and other factors to reveal the underlying noise performance of a facility. The wealth of data that is retained by systems is a valuable research ground to feed future mitigation advice and to support future planning around a facility. Lastly, public engagement has become a strong feature of monitoring systems. It is one thing for a business to employ continuous monitoring to keep a check on noise limits, but unless it is adequately communicating these actions and the resulting compliance to the people that care, the business is not achieving the full benefit of the monitoring program. The thought of releasing information about the noise can be a daunting prospect but the airport industry has recognized the benefit of doing so for some years. It promotes transparency and helps to build the communities appreciation of the noise impact as well as building their understanding of the measures an airport is taking to keep noise levels under control. In Europe, timely reporting of environmental impact is core to the Aarhus convention 2. Originally achieved through the regular publication of written noise reports, these days information is more likely delivered through Web enabled technology where people can gain a richer experience and receive data in a more timely fashion. Brüel & Kjær EMS Page 8

11 Figure 5 Sharing of noise information promotes transparency and improves perception A key aspect of sharing information with the community is about engaging them in the process. It is engagement that builds community understanding and it is the most successful public websites that do this well. Whether it is being able to view traces of noise levels and listen to audio recordings or being able to view flight tracks and measure exactly how close to their property the aircraft came, these websites provide a way to increase environmental capacity by improving perception and understanding. Without improving perception and understanding to increase environmental capacity the operator is limited to just reducing the noise levels. 7. THE APPROACH TO MONITORING Advances in monitoring are not just related to what we measure and what we can achieve with the measurements but technological advances have also changed the entire approach to long term monitoring. Due to technology being able to achieve more, monitoring programs are more effective and much lower cost. This makes it easier for companies concerned about their environmental impact to utilize noise monitoring as a tool to manage this. Technology is able to provide a higher quality result which is more consistent and repeatable. We have already touched on the increased storage capacity on site which has reduced the amount of site visits to transfer data, but advances in communication have eliminated the need for site visits except once per year for routine calibration. The same advances in communications that have brought real time data communication result in the ability to access data via smart phones. Noise monitoring systems can also send noise alerts immediately via or SMS to a variety of platforms. Brüel & Kjær EMS Page 9

12 Technology has also changed the way in which monitoring is established and accessed. Traditionally, customers acquire measurement equipment and a license for software. After commissioning a supplier to implement the system, the customer then takes over all operational tasks relating to the system. In the last decade, many business applications have become available as web-based subscription services, instantly accessible through standard webbrowsers, with no need to burden internal IT resources with installation of yet another application. This trend towards Cloud-Based computing is well established and many monitoring clients now conduct the monitoring programs on this model. Cloud computing is a way to increase capacity or add capabilities on the fly without investing in new infrastructure, training new personnel, or licensing new software. Cloud computing encompasses any subscriptionbased or pay-per-use service that is real time over the Internet. Just as organizations will rent office space and acquire cars on a fully-maintained lease basis, many organizations prefer neither to burden their balance sheets with noise monitoring technology assets nor to add additional maintenance tasks to already-stretched internal staff. Noise instrumentation is now routinely offered on an Asset Managed basis where a simple monthly fee guarantees access to operational facilities. Figure 6 Cloud based computing delivers a wide range of benefits By combining the cloud-based and asset-managed approaches, organizations can engage suppliers not just to provide inputs, but to be responsible for outputs and outcomes. This Outcome-Based approach lowers the total-cost-of-ownership of the monitoring solution by leveraging the instrument suppliers centralized resource pool, establishes agreed service levels around the outcomes, and frees up customer resources to focus on stakeholder management and instead of operating a system. 8. CONCLUSION Technology advances have clearly changed instrumentation, how we can overcome the limitations of monitoring whilst remote from the site, what we can do with the data once we have it and in many cases the entire approach to procuring, installation and operating a monitoring program. Increased capabilities driven by advances in technology mean that attendance on site during monitoring is all but eliminated. In turn this is able to transform how noise professionals Brüel & Kjær EMS Page 10

13 monitor noise freeing them from geographical constraints making it possible, for example, to monitor and advise a construction site in Hong Kong from your offices in San Francisco. Continuous remote monitoring is more effective than ever, allowing for remote investigation and analysis. This means that companies that need to monitor can free themselves from technology and resource constraints and have high quality monitoring services provided by technology driven solutions. The cost of monitoring has reduced significantly and it is now easier than ever to incorporate monitoring into standard business processes so that businesses can manage their noise impact and demonstrate compliance to regulators and communities. 9. REFERENCES 1. Gordon E Moore, Cramming more components onto integrated circuits, Electronics, Volume 38, Number 8, April 19, United Nations Economic Commission for Europe, Aarhus Convention on Access to information, Public Participation in decision-making and Access to Justice in Environmental Matters Brüel & Kjær EMS Page 11