Reflection Tab

In order to perform calculations involving reflections, the following settings are required:

On the „Reflection“ tab (menu Calculation|Configuration), the maximum order of reflection to be calculated is set (non-zero).
Make sure that all objects to be considered in the calculation of reflections (e.g. buildings, barriers, cylinders, 3D-reflectors) are reflective (see Chapter 3 - Obstacles).

CadnaA calculates reflections applying time-efficient algorithms to detect all possible ray paths up to the order specified.

However, the required computation time increases with increasing order of reflection and with increasing number of reflective objects. High reflection orders used in conjunction with large scenarios may lead to unacceptable computation times. A calculation of higher orders of reflection should, therefore, only be used with limited scenarios and with a few reflective objects.

max. Order of Reflection

The maximum order of reflection to be taken into account using the image source method, basically determines the calculation time. For most tasks it is sufficient to just consider the first order of reflection. Higher reflection orders should be used only with limited scenarios comprising a fewer number of objects. Default Setting: 0 Order (direct rays only).

Note

Several guidelines and standards for the calculation of road and railway noise (e.g. RLS-90 RLS-1990 or Schall03 S03-1990) just consider reflections up to the first order. When the options „Strictly acc. to RLS-90“ (see Road Tab) and/or „Strictly acc. to Schall03“ (see Railroad Tab) are activated on the „Road“ resp. „Railroad“ tabs, the setting for the reflection order on the „Reflection“ tab is ignored. In these cases, the calculation is performed only up to and including the first order.

At present, CadnaA calculates reflections up to a maximum order of 20. CadnaA offers to display the ray paths contributing to the level at a receiver (see Displaying Sound Rays).

Conditions for Calculation of Reflection

Search Radius from Source/from Receiver

Up to this distance in meters from the source or from the receiver all the reflective surfaces are detected (default value: 100 m).

Note

When this input box is empty or when the value is 0, no test for reflective surfaces occurs.

Example

Path: Examples\Configuration\Reflection\search_radius_reflector

	setting: up to 1st order, 100 m radius from source and from receiver: All barriers which are located entirely or partially within the two search radii have been detected, provided they have reflective properties and satisfy the reflection condition.
	setting: up to 1st order, 150 m radius from source, 0 m from receiver: The northerly, reflective barrier is detected as well. The easternmost barrier is outside the search radius of the source.

Maximum Distance Source - Receiver

When the receiver is further away from the source than the maximum distance, no reflections will be calculated. This requirement is checked for in addition to the specified search radius for source and receiver (default value: 1000 m).

Example

Path: Examples\Configuration\Reflection\max_distance_source-rcvr

settings:
- maximum distance source-receiver 1000 meters
- calculation up to 1st order of reflection
- 100 m radius around source and receiver:
The reflector is only seen by the receiver at distance x = 500 m, since there the reflector is within the 100 m radius around the receiver and less than 1000 m away from the source. By all the other receivers the reflector is not seen.

settings: as before
The reflector is not seen by the receiver at distance x = 1100 m because it is more than 1000 m away from the source. The reflector is seen by the receiver at x = 999 m, since the latter is less than 1000 m away from the source and the reflector lays within the search radius of 100 m around the source.

Maximum Distance Source - Receiver, Interpolate from

This option offers to interpolate between the region having been calculated with and that region having been calculated without reflections. Interpolation between these regions is particularly useful with grid calculations in order to avoid level jumps at the border of both regions.

The default value is 1000 m. So, no interpolation occurs as there is no transition region (i.e. the value „Interpolate from“ equals the value „Max. Distance Source-Receiver“).
When the value „Interpolate from“ is less than 1000 m (assuming the default maximum distance source-receiver of 1000 m) the effect due to reflection is continuously decreased in the intermediate region.

Example

Path: Examples\Configuration\Reflection\max_distance_source-rcvr

In the examples the maximum distance source-receiver is 1000 m. All other settings correspond to the default setting.

value for "Interpolate from" = 1000 m: The level increase due to reflection visible on the grid in front of the reflecting barrier suddenly ends at a distance of 1000 m (corresponding to the maximum distance source-receiver of 1000 m).

value for "Interpolate from" = 500 m: In the distance range from 500 to 1000 m from the source, the level is interpolated linearly, so that no level changes occur on the grid.

Minimum Distance Receiver - Reflector

When calculating the facade levels at buildings (by using receivers or facade points in conjunction with the Building Evaluation, see Building Evaluation) national regulations specify whether these levels have to be calculated including the reflection by the facade or not.

When the calculation of the facade level does not consider the reflection, the minimum distance receiver - reflector specified here must to be larger than the real distance of the receiver or facade point from the building’s facade surface.

The default value for the minimum distance receiver - reflector is 1 m. This means that for all receivers and facade points being placed closer to building facade no reflection is considered in the calculation.

Note

With a minimum distance of 0 m reflections will always be calculated, provided the building has reflective properties.

Note

When using the Object Snap (see Object Snap) to place receivers along facades the „Distance Point-Facade“ must be smaller than the minimum distance specified here in order to not calculate reflections (default distance: 0.05 m). The same applies regarding the distance of facade points with Building Evaluations (see Building Noise Map, Distance Receiver-Facade (m), default value 0.05 m).

All other reflectors located outside this minimum distance will cause reflections provided the other configuration settings and the respective object properties are adequate.

Minimum Distance Receiver - Reflector, Interpolate to

Here - in contrast to the maximum distance - a larger value than the minimum distance can be specified. For the intermediate region, the level values are interpolated linearly (from „none“ to „full“ reflection).

Note

A smaller value than the minimum distance receiver - reflector has no effect.

Example

Path: Examples\Configuration\Reflection\min_distance_rcvr-reflector

for a receiver at 0.05 m distance off the facade:

close-up at the facade’s surface:

minimum distance receiver - reflector: 1 m (default value), receiver at 0.05 meters off the facade (placed using object snap):
In the region up to 1 m in front of the facade, the levels at receivers, along facades or on the grid are calculated without reflections (i.e. no ray is reflected by the facade). Outside this region (distance > 1 m) the facade reflection is taken into account.

for the lines of equal noise level on the grid:

minimum distance receiver - reflector 1 m (default value), Interpolate to 1 m (default value): A level jump occurs at 1 m distance from the facade.

minimum distance receiver - reflector 1 m (default value), Interpolate to 3 m: The level jump is smoothened by interpolation between 1 and 3 m distance off the facade.

Minimum Distance Source - Reflector

When modeling of sound radiation from facades (see Building Radiation in the manual „Introduction to CadnaA“), the reflection by vertical area sources at the own building is usually taken into account by the directivity index K₀ or DΩ (see Common Input Data, K0 without Ground). In this case, it has to be prevented for considering reflected rays at the own facade in addition.

The default value for the minimum distance source - reflector is 0.1 m. For a source located within that distance in front of the facade no reflection at the rear wall is calculated.

Note

When using the Object Snap (see Object Snap) to place vertical area sources a distance of 0.05 m is applied per default. In conjunction with the minimum distance source - reflector of 0.1 m this setting ensures that no reflection at the own building is taken into account.

For all other sources that are laying outside this minimum distance, the building is reflective provided the other configuration settings are adequate.

Example

Path: Examples\Configuration\Reflection\min_distance_source-reflector

minimum distance source - reflector 0.1 m: As the source with a distance of 0.05 m in front of the facade is located closer than the minimum distance, no reflection at the building occurs.

minimum distance source - reflector 0 m: The calculation of reflections at the own house occurs always. In this case, it must be ensured the directivity index K0 resp. DΩ of the source is set to 0 dB. Otherwise, the reflected component would be considered twice.