I want to eat these strange rocks. Exciting work by @arnequinze made my windy day in #Oostende. #rockstrangers  (at Oostende Strand)

I want to eat these strange rocks. Exciting work by @arnequinze made my windy day in #Oostende. #rockstrangers (at Oostende Strand)

Scattered bits of #shells shelter bits of #sand from the #wind to create #sea shooting #stars. (at Oostende Zeedijk)

Scattered bits of #shells shelter bits of #sand from the #wind to create #sea shooting #stars. (at Oostende Zeedijk)

Dressage. (at Oostende Strand)

Dressage. (at Oostende Strand)

Belgium takes care of its statues. Statues take care of Belgium.  #noborders #freepalestine #mannekenpeace (at Bruxelles - Place Saint Boniface)

Belgium takes care of its statues. Statues take care of Belgium. #noborders #freepalestine #mannekenpeace (at Bruxelles - Place Saint Boniface)

La mitraillette. Toujours un succès chez les enfants. #toys #war

La mitraillette. Toujours un succès chez les enfants. #toys #war

Just realised I fuckin’ love #caravans.

Just realised I fuckin’ love #caravans.

Squashed head. Barbarie.

Squashed head. Barbarie.

These #landscape studies by Erik Dhont @bozarbrussels were very tasty.  (at BOZAR)

These #landscape studies by Erik Dhont @bozarbrussels were very tasty. (at BOZAR)

Oeuf dur. Claude Valois. (at Citadelle de Villefranche sur mer)

Oeuf dur. Claude Valois. (at Citadelle de Villefranche sur mer)

Constellation dans un coin. (at Plage de La Mala)

Constellation dans un coin. (at Plage de La Mala)

One of the most amazing places i visited recently. An old stone mine hiding gardens in the middle of a mysterious island ! (at lithica menorca)

One of the most amazing places i visited recently. An old stone mine hiding gardens in the middle of a mysterious island ! (at lithica menorca)

One of the most amazing places i have visited recently, an old stone mine hiding gardens in the middle of a mysterious island ! (at lithica menorca)

One of the most amazing places i have visited recently, an old stone mine hiding gardens in the middle of a mysterious island ! (at lithica menorca)

Sound Propagation through a Forest Edge: 
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil 
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder 
US Army Corps of Engineers 
Engineer Research and Development Center 
Construction Engineering Research Laboratory 
Champaign , IL 61822

Donald G. Albert and Stephen Decato 
US Army Corps of Engineers 
Engineer Research and Development Center 
Cold Regions Research and Engineering Laboratory 
Hanover , NH 03755

Arnold Tunick 
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.
ZoomInfo
Sound Propagation through a Forest Edge: 
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil 
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder 
US Army Corps of Engineers 
Engineer Research and Development Center 
Construction Engineering Research Laboratory 
Champaign , IL 61822

Donald G. Albert and Stephen Decato 
US Army Corps of Engineers 
Engineer Research and Development Center 
Cold Regions Research and Engineering Laboratory 
Hanover , NH 03755

Arnold Tunick 
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.
ZoomInfo
Sound Propagation through a Forest Edge: 
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil 
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder 
US Army Corps of Engineers 
Engineer Research and Development Center 
Construction Engineering Research Laboratory 
Champaign , IL 61822

Donald G. Albert and Stephen Decato 
US Army Corps of Engineers 
Engineer Research and Development Center 
Cold Regions Research and Engineering Laboratory 
Hanover , NH 03755

Arnold Tunick 
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.
ZoomInfo
Sound Propagation through a Forest Edge: 
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil 
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder 
US Army Corps of Engineers 
Engineer Research and Development Center 
Construction Engineering Research Laboratory 
Champaign , IL 61822

Donald G. Albert and Stephen Decato 
US Army Corps of Engineers 
Engineer Research and Development Center 
Cold Regions Research and Engineering Laboratory 
Hanover , NH 03755

Arnold Tunick 
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.
ZoomInfo
Sound Propagation through a Forest Edge: 
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil 
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder 
US Army Corps of Engineers 
Engineer Research and Development Center 
Construction Engineering Research Laboratory 
Champaign , IL 61822

Donald G. Albert and Stephen Decato 
US Army Corps of Engineers 
Engineer Research and Development Center 
Cold Regions Research and Engineering Laboratory 
Hanover , NH 03755

Arnold Tunick 
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.
ZoomInfo

Sound Propagation through a Forest Edge:
The Influence of Angle of Incidence

http://www.acoustics.org/press/153rd/swearingen.html

153rd ASA Meeting, Salt Lake City, UT

Michelle E. Swearingen – michelle.e.swearingen@erdc.usace.army.mil
Michael J. White, Patrick Guertin, Jeffrey Mifflin, and Timothy Onder
US Army Corps of Engineers
Engineer Research and Development Center
Construction Engineering Research Laboratory
Champaign , IL 61822

Donald G. Albert and Stephen Decato
US Army Corps of Engineers
Engineer Research and Development Center
Cold Regions Research and Engineering Laboratory
Hanover , NH 03755

Arnold Tunick
US Army Research Laboratory
Adelphi , MD 20783

Popular version of paper 2aPAa2 
Presented Tuesday morning, June 5, 2007 
153rd ASA Meeting, Salt Lake City, UT

The way that sound travels through a forest edge has implications for noise mitigation and acoustic detection systems. While the acoustical significance of this unique environment has been noted, it has not been studied in any detail. Acoustical signals that propagate through a forest edge yield complicated pressure-time histories for listeners both within and outside the forest. Several physical processes contribute to this complexity, including the physical structures of the biomass and ground and the microclimate.

An experiment was conducted to determine the influence of a forest edge on acoustical propagation. To simplify the situation, we chose a site with a single-age planted monoculture of regularly-spaced red pine (Pinus resinosa) with an adjacent open field area, on flat ground, having a distinct and straight forest edge. Growth at the forest edge included only red pine, with no additional herbaceous growth. Selecting a site with only these characteristics minimized the number of variables to be considered in the analysis. Figure 1 is a photograph of the test site, taken from the open field and showing the forest edge. Figure 2 is a photograph of the test site, taken from inside the forest and showing the forest edge.


Figure 1: View of the forest edge from the open field.


Figure 2: View of the forest edge from inside the forest. Note the regular spacing of the trees.

Weather during the field experiment was generally sunny and clear, with light winds. Detailed meteorological measurements were logged every five minutes from instrumented towers placed in the open field, at the forest edge, and in the forest interior. Each tower was 13 m high and had sensors at five regularly spaced heights. Figure 3 is a photograph of the tower at the forest edge.


Figure 3: View of the forest edge meteorological tower. Each height is instrumented to record temperature, relative humidity, and wind speed and direction.

Microphones were placed mainly along a line passing from point BP1 in the open field and perpendicularly through the forest edge. Additional microphones were placed along a second line from BP1 to the forest edge at an angle of 25º from the main line. A complete layout schematic is included in Figure 4. For the purposes of this article, only microphones A1-A3 and S1-S3 are considered, and only source point BP1 is considered.


Figure 4: Schematic of the sensor layout. A1-4, S1-5, and L1-3 are all microphone locations. BP1-4 are source locations. MO, ME, and MF are meteorological tower locations. The shaded rectangular area represents the forest and the green hash marks indicate that the forest continues in that direction. Distances are in meters.

Pressure-time histories of individual shots from a propane cannon (bird scare-away device) were recorded for analysis. Signals were processed to obtain peak sound pressure levels (maximum sound pressure attained) and sound exposure levels (total sound) and 1/3-octave band sound exposure levels (SELs), which provide the sound levels in decibels for a range of frequencies collected into groups known as third-octave bands.

By comparing the measured sound levels at locations A1, A2, and A3 to locations S1, S2, and S3, it should be possible to determine whether those levels are affected by the direction from which the sound impinges on the forest edge, or in other words, the angle of incidence. When comparing A1 to S1 and A2 to S2, there is a small difference between them. S1 and S2 are both 2-3 dB lower in level than A1 and A2 respectively for frequencies below 600 Hz. Above 600 Hz, the differences are greater and not as regular. These differences may be due to source directivity and the influence of the path. At 25 m beyond the edge at points A3 and S3, the differences are essentially gone, and the measured signals are essentially identical at those points. This holds true for 1/3-octave band Sound Exposure Levels (SELs), as well as peak sound levels at specific frequencies. After passing 25 m into the forest, the sound level is insensitive to direction of arrival. The signal levels have been homogenized. The 1/3-octave band sound exposure levels are shown in Figure 5. The peak levels are shown in Table 1.

Position

Peak Level (dB)

A1

141 dB

S1

139 dB

A2

127 dB

S2

125 dB

A3

120 dB

S3

120 dB

Table 1: Peak levels (dB) for microphone positions A1-3 and S1-3.

Figure 5: Comparison of A1-3 to S1-3 in 1/3-octave band SEL. Blue lines represent A1-3. Red lines represent S1-3. (-) are A1/S1, (—) are A2/S2, (-.) are A3/S3.

If we instead look at the 1/3-octave band spectrum of the backscattered signals, we see that frequencies below 60 Hz do not backscatter in an organized way. This is expected, as the wavelengths are much greater than the trunk diameters, much like an ocean wave is largely unaffected by a pylon. Frequencies between 60 Hz and 800 Hz behave similarly for the incident and backscattered signals. Above 800 Hz, there is more separation between the backscattered signals at A1 and S1. Further study is needed to deduce the physical reason for this effect.


Figure 6: 1/3-octave band SEL of incident signals (-) and backscattered signals (—) received at A1 (blue) and S1 (red).

So far we have learned that, for small changes in angle of incidence, the direction from which the signal arrives has very little impact on the received signal. We have also determined that, at least for the situation described here, after a sound travels 25 m into a forest, some information about the direction to the source is lost. There are still many things to learn about the acoustic impact of a forest edge. This ongoing project will answer some of the questions, but will also likely raise even more about how sound travels in this complex environment.

This is the GPS audio recording collar for fox the amazing Simon Cacheux has been working hours on for me and for the sake of listening for 24hours to the world through the ears of a fox ! Bits of explanation by the master below ;)

simoncacheux:

The collar for Antoine Bertin’s Fox Project is almost ready to go… We eventually changed the design of the whole thing a bit (no more separate hook). As can be seen on the last picture: servo motor for the hook, gsm antenna, recorder, gps unit, arduino and the 4 batteries (for around 19h of battery life) all fit in! And the collar is indeed suitable for a fox. Looking forward to hearing the result!
To follow the artistic aspects of the project (and many others), just go there : http://antoinebertin.tumblr.com/ and if you’re close to London, look for the fox with a yellow collar!
ZoomInfo
This is the GPS audio recording collar for fox the amazing Simon Cacheux has been working hours on for me and for the sake of listening for 24hours to the world through the ears of a fox ! Bits of explanation by the master below ;)

simoncacheux:

The collar for Antoine Bertin’s Fox Project is almost ready to go… We eventually changed the design of the whole thing a bit (no more separate hook). As can be seen on the last picture: servo motor for the hook, gsm antenna, recorder, gps unit, arduino and the 4 batteries (for around 19h of battery life) all fit in! And the collar is indeed suitable for a fox. Looking forward to hearing the result!
To follow the artistic aspects of the project (and many others), just go there : http://antoinebertin.tumblr.com/ and if you’re close to London, look for the fox with a yellow collar!
ZoomInfo
This is the GPS audio recording collar for fox the amazing Simon Cacheux has been working hours on for me and for the sake of listening for 24hours to the world through the ears of a fox ! Bits of explanation by the master below ;)

simoncacheux:

The collar for Antoine Bertin’s Fox Project is almost ready to go… We eventually changed the design of the whole thing a bit (no more separate hook). As can be seen on the last picture: servo motor for the hook, gsm antenna, recorder, gps unit, arduino and the 4 batteries (for around 19h of battery life) all fit in! And the collar is indeed suitable for a fox. Looking forward to hearing the result!
To follow the artistic aspects of the project (and many others), just go there : http://antoinebertin.tumblr.com/ and if you’re close to London, look for the fox with a yellow collar!
ZoomInfo
This is the GPS audio recording collar for fox the amazing Simon Cacheux has been working hours on for me and for the sake of listening for 24hours to the world through the ears of a fox ! Bits of explanation by the master below ;)

simoncacheux:

The collar for Antoine Bertin’s Fox Project is almost ready to go… We eventually changed the design of the whole thing a bit (no more separate hook). As can be seen on the last picture: servo motor for the hook, gsm antenna, recorder, gps unit, arduino and the 4 batteries (for around 19h of battery life) all fit in! And the collar is indeed suitable for a fox. Looking forward to hearing the result!
To follow the artistic aspects of the project (and many others), just go there : http://antoinebertin.tumblr.com/ and if you’re close to London, look for the fox with a yellow collar!
ZoomInfo
This is the GPS audio recording collar for fox the amazing Simon Cacheux has been working hours on for me and for the sake of listening for 24hours to the world through the ears of a fox ! Bits of explanation by the master below ;)

simoncacheux:

The collar for Antoine Bertin’s Fox Project is almost ready to go… We eventually changed the design of the whole thing a bit (no more separate hook). As can be seen on the last picture: servo motor for the hook, gsm antenna, recorder, gps unit, arduino and the 4 batteries (for around 19h of battery life) all fit in! And the collar is indeed suitable for a fox. Looking forward to hearing the result!

To follow the artistic aspects of the project (and many others), just go there : http://antoinebertin.tumblr.com/ and if you’re close to London, look for the fox with a yellow collar!