Osnabrueck 2011 - Andreić at al: Light Pollution in the Near Infrared 1

Light Pollution in the Near Infrared

Ž. Andreić1, D. Andreić2 and K. Pavlić1

1Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb, Pierottijeva 6, 10 000 Zagreb, Croatia E-mail: zandreic@rgn.hr, kpavlic@rgn.hr

2Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, 10 000 Zagreb, Croatia. E-mail: dandreic@vef.hr

Osnabrueck 2011 - Andreić at al: Light Pollution in the Near Infrared 2

Overview

1. Introduction2. CCD and C-MOS cameras3. visible and infrared sky4. past and future5. conclusions

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Introduction

Light pollution (LP) is usually conected to human vision, so only visible part of EM radiation (light) is considered in studies of LP.

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CCD cameras are sensitive to infra-red (IR) up to 1000 nm!

and there is "LP" in this spectral region too!

IR

C-MOS

CCD

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Modified DSLR camera with filters

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300 400 500 600 700 800 900 1000 1100

Wavelength (nm)

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lati

ve

sp

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l s

en

sit

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y

UV-IR cut

RG-830

no filter

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Monitoring methods: modified DSLR + fish-eye lens + filter

blue UV-IR cut Nd and -IR

25A R72 RG830

Light sources at the horizon can be hiden by a circular lens hood covering horizon up to 10o altitude.

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semi-rural sky, SQM-L: 20.2 at zenith, UV-IR cut

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same sky, RG830 (IR)

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Results

10%

20%

Visible Infrared

0 30 60 90 0 30 60 90

iso-photeeach

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Monitoring methods: modified DSLR + spectrograph

- Fast prismatic spectrograph

- covers 420-1100 nm

- wavelength calibration lamp integrated

- records natural sky spectrum in 5 min at ISO 1600 with a modified DSLR

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LP spectrum, same place

Ne comparison

Sky spectrum around zenith

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Results

0

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1

400 500 600 700 800 900 1000 1100

wavelength (nm)

inte

nsi

ty (

a.u

.)

Na 818,3 nmHP Nalamps

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HP-Na bulbs are the culprit!

HP-Na

sky

MH

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possible solutions

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400 500 600 700 800 900 1000 1100

wavelength (nm)

inte

nsi

ty (

a.u

.)

RG 850

custom interference filter?

H

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Past and future:

HP mercury

HP sodium

metal halide

Incandescent halogen

"white" LED

IRvisible

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Conclusions

1. There is strong LP in the near infrared, and it is produced by the same sources responsible for the LP in the visible part of the spectrum. Sodium bulbs produce very strong IR LP.

2. IR is not as crowded with LP spectral lines as visible part of the spectrum, good filtering is still possible.

3. Scattering of the IR light is not as effective as for the visible light, so the IR sky quality is little better. Also, natural sky brightness is higher in the IR, making LP less prominent.

4. Light cirrus clouds are often prominent in the IR, but are invisible in the visible light.

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Conclusions 2

5. New metal-halide (MH) lamps polute more than sodium HP lamps, both in the visible and in the IR .

6. LED sources polute only in the visible, but show a very worrysome excess of blue light, that should be filtered at the source at any cost.

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The speaker‘s attendance at this conference was sponsored by

the Alexander von Humboldt Foundation.

http://www.humboldt-foundation.de

Acknowledgements

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Thank you for your attention!

Questions?