Environmental Noise Characteristics Research Articles

Quantification of noise levels for the flying drones in accordance with operating condition

This study investigated quantification method of drone noise levels according to various operating conditions through the field measurements. In South Korea, a pilot credential is mandatorily required to operate a drone more than 250 g in accordance with the Aviation Safety Act. Pilot credentials are divided into 4 levels, and Type 1 credential is the highest grade for covering drones of 25 kg to 150 kg which are high-risk unmanned aerial vehicles. For the pilot credential test, a standard flight pattern is defined with various operating conditions such as taking-off, landing, hovering, cruise, triangular and circumferential flights. Accordingly, the environmental noise characteristics according to the standard flight pattern were measured for two types of drones. The measurements are carried out at three points which are 5 m apart from the center of the basic operational range, and one point which is 2 m apart from the center of the route passing-by during the cruise operation. As results, the appropriate evaluation indicators and measurement points were suggested by each operating condition. In addition, repeatability and reproducibility of the measurement results were discussed, and the relationship with environmental noise standards was reviewed.

Experimental investigation on composites incorporating rice husk nanoparticles for environmental noise management

Environmental noise characteristics are determined by factors besides its source. One such factor is reverberation time, which in city canyons tends to be high due to the reflective characteristics of materials commonly used in building facades. Incorporating sound absorbing materials into building facades can help improve urban environments. This research evaluates different facade materials (concrete mix, mortar mix, vinyl spackling, and epoxy resin) incorporated with rice husk nanoparticles (NPs). Rice husk, in addition to presenting good properties for acoustic absorption, is one of the main agricultural wastes worldwide. Additionally, the characteristic of rice husk nanoparticles is correlated with milling time (longer grinding times enhance production of rice husk NPs). Sound absorption coefficients levels increase for compounds with a greater amount of rice husk NPs.

Measurement-outlier robust Kalman filter for discrete-time dynamic systems

This paper proposes a recursive filter for discrete-time linear dynamic systems subject to output outliers or heavy-tailed noises. First, we introduce a weight matrix in the conventional MAP estimation. It is shown that this matrix plays an influential role in the innovation whitening and asymptotic variance of the modified MAP estimation and, consequently, can be used in outlier detection. Then, we propose two different constrained optimization problems to obtain this weight. These constraints, stemming from environmental noise characteristics, help to obtain the weight matrix more precisely, which increases the filtering performance significantly. In the first approach, we introduce a convex optimization problem to minimize the estimation upper bound of the error covariance matrix. The second approach converts the modified MAP estimation to a min–min optimization problem with a concave cost function. Consequently, to reduce the effect of outliers in estimation, a semidefinite program (SDP) is proposed for outlier detection. At last, simulation results show the effectiveness and verify the performance of the proposed filter for dynamic systems in the presence of measurement outliers.

The transfer function method reveals how age‐structured populations respond to environmental fluctuations with serious implications for fisheries management

AbstractFluctuations in wild fish populations result from interaction between population dynamics and environmental forcing. Age‐structured populations can magnify or dampen particular frequencies of these fluctuations, depending on life cycle and species traits. The transfer function (TF) gives a detailed analytical description of these phenomena. In this study, we derive a generalized form of TF to investigate the fluctuations of fish populations in response to species traits and environmental noise characteristics. We found that for semelparous species, fluctuations in fish stocks log‐size are directly proportional to the recruitment elasticity and inversely proportional to the age of maturity, and for iteroparous species, fluctuations in fish stocks log‐size are inversely proportional to the adult lifespan. In addition to the already known effect of cohort resonance (increased sensitivity to environmental fluctuations on cohort timescales in the elastic range of recruitment elasticity), we find a stock resonance effect (increased sensitivity to environmental fluctuations on double cohort timescales in the inelastic range of recruitment elasticity). These results were then applied to fisheries management. The relationship between fishing mortality and species‐specific variability of fish stocks was formalized. In accordance with this analysis, precautionary levels for different catches were estimated.

Field Test Research on Environmental Noise Characteristics in the Throat Area of Metro Depot

Environmental noise pollution is the primary environmental problem faced by the superstructure of metro depots. The throat area of depot is prone to high wheel-rail impact noise due to the use of seam lines, multiple joints, turnouts and small radius curves. The noise exerts through fire and ventilation openings on the side walls, which may cause high annoyance to the residents in the superstructures both on the upper cover and surrounding areas. In this paper, a field test was condected on the environmental noise in the throat area of metro depot. The noise of the trackside and adjacent open space were recorded, and the time-frequency domain characteristics and statistical characteristics and attenuation law of the noise generated by train operation in the throat area were analyzed. The research results have certain guiding significance for the prediction and control of noise in the throat area of the depot.

Effect of elastic rubber mats on the reduction of vibration and noise in high-speed elevated railway systems

In the development of a high-speed railway system, controlling the vibration and noise caused by the system plays an important issue, since the vibration and noise have an influence on the surrounding environment. This study describes the field experiment conducted in September 2015 on the Chengdu–Dujiangyan high-speed railway system where elastic rubber mats – the only countermeasure that is currently applied to reduce vibration and noise in high-speed elevated railway systems in China – were installed in September 2010. The effects of mats under the tracks on noise and vibration were evaluated and analyzed systematically compared to the tracks without mats in the following three aspects: vertical wheel–rail forces; vibration characteristics of the track system, bridge, and ground in combination with the environmental noise characteristics in several frequency domains; and the ride comfort and the interior noise of the vehicle. The results indicate that mats have a negligible effect on the vertical wheel–rail forces, ride comfort, and the interior noise of the vehicle. However, even though they significantly reduce the vibration of the base slab, bridge, and the ground below the mats, vibration of the rails and track slabs above the mats is increased, especially at low frequencies. Mats can also effectively reduce the bridge-borne noise but have little influence on the far-field noise. Furthermore, their control effect on environmental noise and vibration was evaluated in September 2010 and September 2015, showing that mats could effectively minimize the environmental vibration and bridge-borne noise after five years of practical operation, although their control effect declined as their stiffness increased.

Evidence theoretic classification of ballistic missiles

In this paper, using the Dempster–Shafer theory (DST) of evidence, a new decision criterion is proposed which can quickly classify airborne objects without any a priori knowledge, whose data are laced with environmental noise characteristics, within 10seconds (10s) from the time it is detected. Kinematic parameters of an airborne object received from radars are used to classify it into one of the six classes, which include three levels of ballistic target discrimination, aerodynamic, satellite and unknown. The DST is chosen as it can suitably handle the element of uncertainty, limited a priori data and short observation times that exist with the data acquired for the purpose of classification. The focus of the work is on ballistic targets in a theater of war. The approach is compared with the popularly known k-NN and decision tree techniques and is found to perform better with the chosen data sets. This approach is tested using both real flight test data and simulated data.

Clutter losses and environmental noise characteristics associated with various LULC categories

To enhance the accuracy of propagation predictions for broadcasting and land mobile applications, a more accurate characterization of clutter loss and of environmental noise has been needed. A series of tests was performed to quantify the environmental RF noise levels associated with various types of ground clutter and to quantify the effects of ground clutter on RF propagation path loss. Tests were performed at 162, 460, and 860 MHz in four different localities in the United States. Each had very different land clutter, as characterized by the land use land cover (LULC) categories used in the United States. It was found that the numbers currently in use by industry for clutter loss are, in general, slightly less than the observed values. Both the clutter loss and noise results can be applied to system design.