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From page 42... ... 42 Four approaches or tools to adjust modeled sound levels for meteorological effects are: • Statistical regression models, • Look-up tables, • Engineering models, and • PE models. Each approach uses meteorological parameters in diverse ways and in varying degrees of complexity. Read the entire page →
From page 43... ... Conceptual Models and Tools 43 While the vertical wind speed profile is important for determining the sound speed profile, it is not directly measured at most National Weather Service weather stations. Wind shear can be measured by anemometers at multiple heights, or through Lidar, Sodar, or weather balloon radiosonde measurements. Read the entire page →
From page 44... ... 44 How Weather Affects the Noise You Hear from Highways As part of this project, the research team created a spreadsheet that uses an AERMET file to estimate the wind speed profile using the formula in Equation 2. This is discussed further in the following section. Read the entire page →
From page 45... ... Conceptual Models and Tools 45 phenomenon and already considered in all engineering sound models.) However, the vertical temperature profile will directly affect the sound speed profile. Read the entire page →
From page 46... ... 46 How Weather Affects the Noise You Hear from Highways shear in stable conditions. Alternatively, turbulence intensity can be directly measured using relatively inexpensive logging anemometers. Read the entire page →
From page 47... ... Conceptual Models and Tools 47 The methodology is based on the evaluation of the three atmospheric parameters related to noise propagation: wind speed changes with height (wind shear) , temperature changes with height (lapse rate) Read the entire page →
From page 48... ... 48 How Weather Affects the Noise You Hear from Highways model that was most useful is one that uses data that is readily available from AERMET using NWS data. Note that the effective sound speed gradient can be calculated using the AERMET Sound Speed Profiler spreadsheet tool described in this chapter. Read the entire page →
From page 49... ... Conceptual Models and Tools 49 • The interaction of distance with the sound speed gradient, since the distance from the highway affects the shape of the sound speed gradient effect (LogMicDist * c_effp30) Read the entire page →
From page 50... ... 50 How Weather Affects the Noise You Hear from Highways The two drawbacks of the NCHRP Report 791 tables are that they use the temperature lapse rate, which is not easily measured, and the tables did not show combinations of meteorological conditions. That is, the NCHRP Report 791 tables can only be used where one of the two following conditions are true: the vector wind speed is zero or the temperature lapse rate is zero. Read the entire page →
From page 51... ... Conceptual Models and Tools 51 simplifications made during the modeling process. The simplifications occur for the following reasons: • In the measurements, background levels existed and even though low still represent a "floor" to the measurements like what is expected in TNM modeling. Read the entire page →
From page 52... ... 52 How Weather Affects the Noise You Hear from Highways eliminating the variation in traffic type and flow. FHWA TNM Reference Energy Mean Emission Level (REMEL) Read the entire page →
From page 53... ... Conceptual Models and Tools 53 • Table 16 shows the meteorological effect only as a function of the 10-meter wind speed. It includes all measurements, not just those under zero temperature lapse conditions. Read the entire page →
From page 54... ... 54 How Weather Affects the Noise You Hear from Highways Temperature Profile Distance to Highway (m) 15 30 60 120 240 480 960 Strong lapse 0 -2 -3 -4 -6 -6 -7 Lapse 0 -2 -2 -3 -5 -6 -6 Zero 0 0 0 1 1 0 0 Inversion 0 1 2 3 5 5 2 Strong inversion 0 1 1 2 4 2 -1 * Read the entire page →
From page 55... ... Conceptual Models and Tools 55 Engineering Models Engineering models are generally based on physical principles and can be used to model diverse types of site-specific conditions. Engineering models tend to generalize, which allows for ease-of-use and reasonable calculation times. Read the entire page →
From page 56... ... 56 How Weather Affects the Noise You Hear from Highways model represents the practical state-of-the-art direct implementation that can be achieved in TNM. Such a model would be able to handle multiple terrain features more precisely than could be achieved with look-up tables or regressions while at the same time being able to produce results much faster than a research model. Read the entire page →
From page 57... ... Conceptual Models and Tools 57 Adjustments from simple regression models offer relatively fast computation times. In addition, changes in the required adjustments due to subtleties in parameter levels can be smoothed out in the statistical model. Read the entire page →

From page 42...

... 42 Four approaches or tools to adjust modeled sound levels for meteorological effects are: • Statistical regression models, • Look-up tables, • Engineering models, and • PE models. Each approach uses meteorological parameters in diverse ways and in varying degrees of complexity.