A review of transport noise indicators

TL;DR: In this paper, a review of the main transport noise indicators, both the general acoustic ones and those used for specific transport modes, is presented, with a critical analysis of the strengths and weaknesses of these indicators, as well as a section discussing the framework in which they work.

About: This article is published in Transport Reviews.The article was published on 2012-08-21 and is currently open access. It has received 17 citations till now. The article focuses on the topics: Environmental noise & DPSIR.

Summary

1 Introduction

• The absolute magnitude is a fundamental astronomical parameter.
• This brightness is determined by the asteroid’s size (D, diameter in km) 2 and geometric albedo (pV); the latter parameter, which is used to quantify the intrinsic reflectance of the surface, is related to surface composition and texture.
• 2 D is the diameter of a sphere having the same projected surface area as the asteroid.
• Therefore, the authors must extrapolate from the phase angle of observation to zero degrees using what they know about the variation of the magnitude as a function of phase angle.

2.1 H, G Magnitude Phase Function

• The H, G phase function for asteroids can be described as follows.
• Due to the peculiarity of the Mercury phase curve at large phase angles, it was excluded from the development of the H, G phase 9 function.
• More than 20 years since its adoption, there are reasons to try and improve the H, G phase function.
• This function still does a reasonably good job in fitting phase curves for many asteroids, especially in the region from ∼10◦ to ∼60◦.

2.2 Stochastic Optimization

• The authors make use of a stochastic optimization method for the basis functions that is, in principle, independent of any a priori analytical choices for the shape of the functions.
• In optimizing the basis functions, the data are properly weighted by the asteroid groups and number of members within each group.
• It is important to require that the basis functions be nonintersecting at phase angles most typically covered by observations: should the basis functions intersect, all resulting phase functions would pass through the point of intersection, which would be in disagreement with observational data.
• The authors group the individual asteroid phase curves based on their similarities and differences so as to guarantee a balanced coverage of phase-curve variability.
• In characterizing the goodness of the linear least-squares fits for the individual brightness phase curves, the authors make use of the rms values of the fits (in mag, again).

2.3 Monte-Carlo Inverse Methods

• For a given magnitude phase function, the a posteriori probability density function (p.d.f.) for the parameters a is obtained from (cf. Eq. 11) p(a)∝ exp[−1 2 χ2(a)], (16) where χ2 denotes the product of the residuals in a row vector (observed minus computed), the covariance matrix for the random observational errors, and the residuals in a column vector.
• In what follows, for simplicity, the covariance matrix is assumed to be diagonal.
• If the model is linear, p(a) is a multivariate Gaussian p.d.f. and can be Monte-Carlo sampled using standard methods, whereafter samples of dependent nonlinear parameters follow in a straightforward way.

3.1 Optimizing the H, G Phase Function

• The authors first attempt to obtain an improvement of the H, G phase function consists of trying to derive improved expressions for the basis functions Φ1(α) and Φ2(α).
• Making the composite curves for groups I-IV is presently required in order to obtain a coverage as a function of the phase angle dense enough for successful optimization of basis functions.
• Note that the phase curves of (24) Themis, (44) Nysa, (1862) Apollo, and the Moon have been included in the derivation of the new magnitude phase function, which partly explains the remarkably small rms-values for the H, G1, G2 fits for these objects.

4 Conclusions

• The authors have developed a three-parameter cubic-spline H, G1, G2 magnitude phase function for asteroids that provides excellent fits to magnitude-phase observations.
• The authors have shown that this three-parameter phase function succeeds in removing the inability of the H, G magnitude phase function to adequately fit the phase curves of high-albedo and low-albedo asteroids.
• Furthermore, the H, G1, G2 phase function has allowed for the development of the nonlinear two-parameter H, G12 phase function that provides predictive power for small numbers of observations (sparse observational data) better than the H, G phase function.
• The authors point out that, should a new type of asteroid photometric phase-curve data become available, it is possible to revise the magnitude phase functions using the methods currently presented.
• Finally, the new phase functions can turn useful in the interpretation of Gaia and Pan-STARRS photometry of asteroids.

Figures

Table 1 Synthesis of strengths and weaknesses and use of general acoustic and general environment noise indicators

Table 3 Synthesis of strengths and weaknesses and use of air noise indicators

Figure 1 Relationships among the noise indicators

Table 2 Synthesis of strengths and weaknesses and use of road and rail noise indicators

Frequently asked questions

Q1. What are the future works in this paper?

The possibility to use short-time measures to calculate Lden is critical for a good use of past efforts and to reduce monitoring costs. To this extent the measurement techniques are important to distinguish between potential ( Lden ) and real disturbance. The traffic micro-simulation models, more suited to apprehend the kinematic characteristics, can help ( Chevallier et al., 2009 ; Beuving and Hemsworth, 2006, but costs are high as regards the potential improvements. Of course, simpler methods are welcome and better measured data will allow a good trade-off between simplification and precision, also because measurements remain essential to calibrate the models ( e. g. for the evolution of the vehicle fleets ). 

Q2. What are the contributions in this paper?

The paper presents a review of the main transport noise indicators, both the general acoustic ones and those used for specific transport modes. A critical analysis of the strengths and weaknesses of those indicators is provided, as well as a section discussing the framework in which they work, and suggestions for their best use, aimed at assisting decision-makers to ascertain their role in the evaluation process of the transport systems. 

Q3. What are the effects of noise on human health?

Noise induces social and behavioural effects, notably annoyance and sleep disturbance; from a medical point of view, the effects of noise on human health are also well known: hearing impairment, speech intelligibility, physiological dis-functions, mental illness, performance reduction, cardiovascular diseases (WHO, 1999; WHO, 2011). 

Q4. How much time is it necessary to carry out measurements?

carrying out measurements is a very expensive exercise and, to meet the Directive requirements properly, long time measurements are necessary. 

Q5. What is the difficulty of achieving the targets?

The difficulty to attain those targets is that 80% of people live in the urban areas, where transport infrastructures represent the most important source of noise. 

Q6. what is the use of factor analysis in the economic evaluation of noise effects?

While in Europe the use of Lden and Lnight indicators for the economic evaluation of noise effects is now common, this paper shows that decision-makers should jointly use noise and socio-economic variables to fully support their decisions. 

Q7. What is the main reason why the general acoustic indicators are useful?

The general acoustic indicators are useful when it is just important to quantify the noise produced and, for this reason, both road and rail noise indicators stem from Leq, SEL and Lxx.