All Optical Fog_MI

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All-optical Fog Sensor for Determining the FogVisibility Range in Optical Wireless

Communication Links

Muhammad Ijaz, Zabih Ghassemlooy, SeniorMember, IEEE,Hoa Le-Minh, Sujan Rajbhandari,

Member, IEEEOptical Communication Research Group, School of computing, Engineering and

Information Sciences, Northumbria University, UK

Email: [email protected]


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Structure of the Talk

Motivations

Optical Wireless Communication

Why Fog Sensor

Design of the Fog Sensor

Fog Sensor and Visibility

Results

Conclusions


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Motivations

Free space Optical Communication (FSO) Link

Why Fog SensorThe meteorological definition of fogis when the link visibility is less than 1 km.1,2

The visibility is the prime parameter for investigating the affects of fog on outdoor FSOsystems performance and availability.

The visibility data is not available for real sites of the FSO links due to the high implementationcost of transmissometer. In this paper we introduced a laboratory optical fog sensor which hasbeen designed to characterise the link visibility for different fog channel conditions.

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1. H. Willebrand, and B. S. Ghuman, Indianapolis, IN: SAMS publishing, 2002.2. M. S. Awan, L. C-Horvath, S. S. Muhammad, E. Leitgeb, F. Nadeem, and M. S. Khan, J. of Communications, 4(8), pp. 53 -

545, 2009.


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Design of the Fog Sensor

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Figure 1. (a) Optical fog sensor, Distance between LEDand Receiver is 13 cm and (b) atmospheric chamber.The volume of atmospheric chamber is 5.50.30.3 m3.

Sound Card

Photo-DetectorTransmitter

=880nm

Amplification

Sound Card

Amplification

Computer

Figure 2. Block diagram of fog sensor.


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Fog Sensor and Visibility

Meteorological visibility V can be expressed as function of theatmospheric attenuation coefficient yusing the visual threshold Tth byKoschmieder Law:1

The attenuation coefficient can be calculated from the Beer-Lambert

law given by 1-3

I(f)andI(0) are the intensity of the optical signal with and without fog,respectively.

Note that the fog sensor output was normalized to 1 and 0 without fog andwith a dense fog, respectively. So, the value of fog sensor is calibrated between1 and 0 depending on the fog density within the chamber.

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1. A. Prokes, J. of Optical Engineering, 48(6), pp. 066001-10, 20.2. M. S. Awan, L. C-Horvath, S. S. Muhammad, E. Leitgeb, F. Nadeem, and M. S. Khan, J. of Communications, 4(8), pp. 53 - 545, 2009.3. M. A Naboulsi, F. de Fornel, H. Sizun, M. Gebhart, E. Leitgeb, S. S. Muhammad, B. Flecker and C. Chlestil, Proc. of SPIE, Optical

Engineering, 47(3), pp. 036001.1 - 036001.14, 2008.


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Results

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0 5000 10000 150000

1000

2000

3000

4000

5000

6000

Abs.

Magnitu

de

Frequency [Hertz]

Without fog

0 5000 10000 150000

1000

2000

3000

4000

5000

6000

Abs.

Magnitude

Frequency [Hertz]

with Fog

The received signals in frequency domain with and without fog are shown .The absolute magnitude level of the received signal without fog is 5500which is equal to 1 V, whereas with fog, the level is 2900 equal to 0.5304 V.


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Results-cont.

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00.10.20.30.40.50.60.70.80.910.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Transmittance

Visibility(Km)

Light Fog Moderate Fog

The transmittance (T) of the fog sensor versus the visibility in kmfrom light to moderate fog.


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Results-cont.

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0.4 0.5 0.6 0.7 0.820

25

30

35

40

45

Visibility(Km)

Attanuation(dB/Km)

0 0.2 0.4 0.6 0.8 120

25

30

35

40

45

Transmittance(T)

A

ttanuation(dB/Km)

(a) Experimental visibility versus attenuation (dB/km) and (b) transmittance of the optical fog

sensor versus the attenuation coefficient (dB/km).

The attenuation exceeds 45 dB/km as the visibility drops below 400 m, for moderatefog case. This is inline with the attenuation data reported in1,2for the visibility rangeless than 500 m.

(a) (b)

1. I. I. Kim, B. McArthur, and E. Korevaar, Proc. of SPIE, 4214(issue??), pp. 26 - 37, 20012. A. Prokes, J. of Optical Engineering, 48(6), pp. 066001-10, 2009.


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Conclusions

In this paper we have shown the application of an all optical fogsensor in an FSO system for measuring optical attenuation dueto light-to-moderate fog in a laboratory based atmosphericchamber.

Using the Koschmieder law, the fog sensor is used to determinethe visibility (and attenuation) in the range of 0.37 1 km andabove.

Work to develop the fog density measurement tool for allranges of visibility is in progress and the results will bepublished in due course.

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Special Thanks for

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Prof. Z. GhassemlooyDr. Hoa Le-MinhDr. Sujan Rajbhandari

All colleagues in OCRG&

Your Attention


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References

1. P. Mandl, P. Schrotter, and E. Leitgeb, Wireless synchronous broadband last mile access solutions formultimedia applications in license free frequency spectrums, 6th International Symposium onCommunication Systems, Networks and Digital Signal Processing, pp. 110 -113, 2008.

2. A. K. Majumdar, and J. C. Ricklin, Free-Space Laser Communications, Principles and Advantages, SpringerScience, LLC, 233 Spring Street, New York, NY 10013, USA, 2008.

3. O. Bouchet, H. Sizun, C. Boisrobert, F. de Fornel, and P. Favennec, Free-space optics, propagation andcommunication, ISTE, pp.87 - 127, 2006.

4. I. I. Kim, B. McArthur, and E. Korevaar, Comparison of laser beam propagation at 785 nm and 1550 nmin fog and haze for optical wireless communications, Proc. of SPIE, 4214(issue??), pp. 26 - 37, 2001.

5. H. Willebrand, and B. S. Ghuman, Free space optics: enabling optical connectivity in today's Network,Indianapolis, IN: SAMS publishing, 2002.

6. M. S. Awan, L. C-Horvath, S. S. Muhammad, E. Leitgeb, F. Nadeem, and M. S. Khan, Characterization offog and snow attenuations for free-space optical propagation, J. of Communications, 4(8), pp. 53 - 545,2009.

7. M. A Naboulsi, F. de Fornel, H. Sizun, M. Gebhart, E. Leitgeb, S. S. Muhammad, B. Flecker, and C. Chlestil,

Measured and predicted light attenuation in dense coastal upslope fog at 650, 850, and 950 nm for free-space optics applications, Proc. of SPIE, Optical Engineering, 47(3), pp. 036001.1 - 036001.14, 2008.

8. A. Prokes, Atmospheric effects on availability of free space optics systems, J. of Optical Engineering,48(6), pp. 066001-10, 2009.

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