Assessing and Controlling Blast Noise Emission

Dr. Larry Pater | U.S. Army Engineer Research and Development Center (ERDC)

SARNAM™ Noise Impact Software

Background

Weapons noise compromises the Department of Defense’s (DoD) ability to maintain access to resources necessary for military training and testing. Community reactions to military noise include complaints, damage claims, legal action, political pressure, and other efforts to curtail the noisy activity. Noise concerns have prompted installations to relocate training, impose firing curfews (both time of day and day of the week), and close ranges. Such short-term-solution decisions, if made without reliable noise management technology, can needlessly hamper training mission execution and ultimately impact soldier proficiency and survival. Noise impact assessment software can guide planning decisions to minimize noise impacts on soldier and civilian health and welfare. Impulsive noise from military weapons training and testing is not governed by national laws; consequently, noise management consists of striking a balance between mission execution and environmental quality. Reliable guidance regarding noise level reduction under a wide range of conditions is arguably more critical than the absolute accuracy of noise level predictions for specific conditions.

The military noise impact assessment software, or noise model, known as SARNAM™ enables calculation and display of noise contours for small arms ranges. The name SARNAM™ is an acronym for Small Arms Range Noise Assessment Model. Input options include the type of weapon and ammunition, number and time of shots, range size and structure, noise dose metrics, and assessment protocols. The model accounts for muzzle blast and projectile sonic boom spectrum and directivity, which facilitates accurate sound level prediction and interpretation of receiver response. SARNAM™ noise level predictions are based on the mean expected value of noise level metrics for mild downwind sound propagation conditions; this calculation is used in all directions, which moderately over-predicts noise levels in some regions. SARNAM™ is most useful as an environmental planning tool to address unwanted noise as an environmental attribute in the community; it can be used to avoid siting new noise-sensitive land uses in areas impacted by military noise and to guide mitigation of environmental impacts of operational plans or new facilities.

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Objectives of the Demonstration

The overall objective of this project was to validate and demonstrate the SARNAM™ small arms noise impact assessment software under typical conditions. The “validation” aspect of the project sought to test the accuracy of SARNAM™ by comparing calculation results with comprehensive noise monitoring data to judge noise level prediction accuracy. The demonstration aspect of the project sought to evaluate the software utility and cost during realistic noise management consultation. The software was used to predict noise contours associated with the operation of a proposed new range and was then used to explore revisions to the range location and design to reduce the noise level in the adjacent community. The primary performance measures were the amount of noise dose reduction, the cost of use, and the projected cost savings.

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Demonstration Results

This project had two primary aspects: validation and demonstration. The purpose of the validation aspect of the project was to verify the accuracy of SARNAM™ noise contour calculations. The project also resulted in information regarding how best to employ the software. Each element of the application, particularly calculation algorithms, had been validated under controlled conditions prior to the present project. This project planned to test the combination of all elements under actual conditions by measuring community noise levels in training scenarios at a military installation during an entire year, then comparing the measured levels with SARNAM™ calculated results. The goal of agreement within 5 dB was not met for several reasons. The monitoring period was cut short by an unexpected closure of the ranges, and only summer, not the typically more noisy winter weather conditions were sampled. Analysis of the data pointed out the critical consequences of inaccurate range firing data for determining metric values, particularly annual averages. The results of the validation support the need for an option in SARNAM™ to select among a variety of weather classifications, rather than the current downwind-only model, to achieve improved accuracy under more well-defined weather conditions. The results emphasize that, given the always-present uncertainties in propagation conditions and operation parameters (e.g., weapon, location, and number of shots) that influence sound level predictions, it is not reasonable to expect agreement between predictions and spot measurements. The software is very useful in determining the effects of changes in facilities and operations; these effects are valid regardless of uncertainties and ephemeral conditions.

The demonstration aspect of the project evaluated the utility of SARNAM™ in dealing with realistic operational noise problems. The software was used to assess the noise emission from a proposed new firing range and to explore and evaluate options to reduce community noise impact. Options were identified that provided 5- to 10-dB reductions, which exceeded the goal of a 5-dB reduction, by moving the range location and adding noise barriers. Prior to SARNAM™, the only way to assess small arms noise impact was by manual hand calculation of the expected noise environment in combination with on-site noise monitoring. SARNAM™ was shown to reduce the labor and cost of small arms noise analysis by 65%, which significantly exceeds the 20% cost reduction goal. SARNAM™ was demonstrated to be an effective means for reducing community noise to maintain combat training throughput.

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Implementation Issues

This project provided the first opportunity to test SARNAM™ exhaustively and in detail for accuracy and performance in assessing training noise impact under conditions of actual training at an installation over a protracted time period. The utility of the software for noise mitigation was demonstrated. An extremely favorable cost performance was also shown. The project revealed the extreme importance of reliable training activity data, particularly regarding the type of weapons and the number of rounds fired on each range throughout the assessment period. The noise monitor measurements showed the extreme variability of received noise level. The lack of agreement between calculated and measured noise levels led the researchers to conclude that there is the need to modify SARNAM™ to offer the user a selection of weather conditions. This has been done for two other blast noise models and was intended for SARNAM™, but prevented by development budget cuts. SARNAM™ remains the only software package available to calculate and display weapons noise contours due to weapons impulsive noise, which greatly facilitates assessment of noise impacts and evaluation of noise mitigation options. Results of this project will guide improvement of current and new noise impact assessment software. Results of this study are also of value for guiding how DoD conducts noise impact assessment. The difficulty of obtaining accurate data for the number of rounds fired means that average noise metric values are of dubious accuracy; this is one reason for using single event metric noise levels, since weapon type and location are comparatively easy to ascertain accurately. This project will result in improvement in noise assessment software and procedures that will contribute to sustainable training capability. The project confirmed that the most important purpose of a noise model such as SARNAM™ is not to predict the absolute noise level in the community but to serve as a mitigation tool to manage noise disturbance and environmental quality.

End user—U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM), contractors who perform noise assessments for installations, and installation personnel including master planners, trainers, and range operators—considerations include the accuracy of the software, its cost, and ease of use. The software runs on common personal computers that utilize the Windows™ operating system. The demonstration/validation project used commercially available noise monitoring equipment. The Army developed the SARNAM™ software and hence there are no proprietary considerations. Implementation cost consists essentially of learning to use the software, which is facilitated by expertise in acoustics and familiarity with military weapons systems. Noise emission depends strongly on the type of weapons fired, which is dictated by training requirements. The noise dose in the community can be influenced by other controllable factors, particularly the location of the firing, the design and orientation of the range, the time and weather conditions when the firing occurs, and the number of noise events.

There are no national regulations regarding weapons blast noise. Current “regulation” amounts to self-regulation by the installation to maintain noise at levels acceptable to community residents. This is done by a combination of technology, planning, and public outreach. Information generated by SARNAM™ is used by USACHPPM in consultation with installations to minimize noise problems and is available to installations and the public. Noise models such as SARNAM™ have been formally integrated into Huntsville range design manuals.

SARNAM™ is optimally used as an environmental planning tool to address unwanted noise as an environmental attribute in the community at large rather than a regulatory compliance tool since there are no legally binding criteria for human exposure to noise that support “compliance” levels outside the facility perimeter. Calculated noise contours are used as planning tools for land use guidelines. SARNAM™ can be used to avoid siting new noise-sensitive land uses in off-post areas impacted by military noise as well as to plan military facilities and operations to minimize community noise levels.

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BNOISE2™ Noise Impact Software

Background

Weapons noise compromises the Department of Defense’s (DoD) ability to maintain access to resources necessary for military training and testing. Community reactions to military noise include complaints, damage claims, legal action, political pressure, and other efforts to curtail the noisy activity. Noise concerns have prompted installations to relocate training, impose firing curfews (both time of day and day of the week), and close ranges. Such short-term-solution decisions, if made without reliable noise management technology, can needlessly hamper training mission execution and ultimately impact soldier proficiency and survival. Noise impact assessment software can guide planning decisions to minimize noise impacts on soldier and civilian health and welfare. Impulsive noise from military weapons training and testing is not governed by national laws; consequently, noise management consists of striking a balance between mission execution and environmental quality. Reliable guidance regarding noise level reduction under a wide range of conditions is arguably more critical than the absolute accuracy of noise level predictions.

The military noise impact assessment software, or noise model, known as Blast Noise Version 2 (BNOISE2™) enables assessment of high-energy impulsive noise impacts via calculation and display of noise contours for large arms, including explosive charges, artillery, armor, and missiles. The software was updated in the late 1990s, replacing the previous version known as MicroBNOISE. BNOISE2™ is useful as an environmental planning tool to address unwanted noise as an environmental attribute in the community. It can be used to avoid siting noise-sensitive land uses in regions of the adjacent community as well as to assess mitigation of environmental impacts of operational plans or new facilities.

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Objectives of the Demonstration

The overall objective of this project was to validate and demonstrate the BNOISE2™ noise impact assessment software under typical conditions. The validation aspect sought to test the accuracy of BNOISE2™ by comparing calculation results with comprehensive noise monitor data to judge noise level prediction accuracy. The demonstration aspect sought to evaluate the software utility and cost during realistic noise management consultation.

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Demonstration Results

This project had two primary aspects: validation and demonstration. The purpose of the validation aspect of the project was to test the accuracy of BNOISE2™ noise contour calculations. Each element of the application, particularly acoustical emission models and propagation calculation algorithms, had been validated under controlled conditions prior to the present project. The validation portion of this project was designed to evaluate the prediction accuracy of the software under actual conditions by measuring noise levels in the environs of a military training installation during an entire year, then comparing the measurements with BNOISE2™ predictions; the performance goal was agreement within 5 dB. The validation effort was unfortunately not fully successful. After noise monitoring was complete, it was discovered that the microprocessor-based Norsonics™1 121 noise monitors incorrectly calculated the noise level metrics that researchers planned to use for comparison with BNOISE2™ predictions. Accurate values of a-octave-band spectrum unweighted sound exposure level (SEL) for each event had been recorded, from which the needed metric values could be calculated, though only at considerable cost. A lack of reliable data regarding the firing that occurred during noise monitoring further hampered the validation effort. Project researchers and ESTCP officials agreed to not devote substantial additional resources to analysis of the field validation data. The experience of the validation effort provided valuable insight regarding how best to employ the software and also guided evolution of improved impact assessment methodology for high-energy impulsive noise. Experience gained during the attempted validation, along with concurrent noise consultation experiences, culminated to convince the research team that average-noise protocols do not adequately assess blast noise impacts. This project was a major influence that led to a change in the way the Army assesses blast noise, so it was by no means unsuccessful. This project will have significance well beyond demonstration and validation of the noise models. It was the first comprehensive and objective evaluation of several aspects of correlation between noise impact assessment procedures and actual installation activity. It will help to shape more effective noise impact management procedures and tools for the future.

The demonstration aspect of the project evaluated the performance and cost of BNOISE2™ in assessing and mitigating the impact of additional noise due to increased operations associated with Army Modular Force Transformation restationing. Evaluation of various training scenarios and range siting options enabled impact assessment and identification of mitigation options that without BNOISE2™ could not have been accomplished quickly enough to meet the NEPA document preparation schedule. BNOISE2™ was shown to reduce the labor and cost of noise analysis by at least 67%, substantially exceeding the 20% goal. This improved efficiency enables the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) to accomplish many more noise consultations each year. Additional substantial cost savings are realized as a result of effective management of noise emission from training and testing ranges. The software is very useful in determining the effects of changes in facilities and operations; these effects are valid regardless of uncertainties and ephemeral conditions.

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Implementation Issues

End user—USACHPPM, contractors who perform noise assessments for installations, and installation personnel including master planners, trainers, and range operators—considerations include software accuracy, implementation cost, cost savings, and ease of use. The U.S. Army developed BNOISE2™ in-house at the ERDC/CERL, so there are no proprietary considerations. Implementation cost consists essentially of learning to use the software, which is facilitated by familiarity with acoustical principles and military weapons and training practices.

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Points of Contact

Principal Investigator

Dr. Larry Pater

U.S. Army Engineer Research and Development Center (ERDC)

Phone: 217-373-7253

Fax: 217-373-7251

Principal Investigator

Dr. William Russell

CHPPM

Phone: 410-436-3829

Fax: 410-436-1026

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