Abstract

A prototype auroral hyperspectral all-sky camera has been constructed and tested. It uses electro-optical tunable filters to image the night sky as a function of wavelength throughout the visible spectrum with no moving mechanical parts. The core optical system includes a new high power all-sky lens with F-number equal to f/1.1. The camera has been tested at the Kjell Henriksen Observatory (KHO) during the auroral season of 2011/2012. It detects all sub classes of aurora above ~½ of the sub visual 1kR green intensity threshold at an exposure time of only one second. Supervised classification of the hyperspectral data shows promise as a new method to process and identify auroral forms.

© 2012 OSA

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References

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  1. W. L. Wolfe, Introduction to Imaging Spectrometers (SPIE Press, 1997).
  2. F. Sigernes, D. A. Lorentzen, K. Heia, and T. Svenøe, “Multipurpose spectral imager,” Appl. Opt.39(18), 3143–3153 (2000).
    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef]
  5. R. Nakatsuji, PerkinElmer - Caliper Life Sciences, 68 Elm St., Hopkinton, MA 01748, USA (personal communication, 2012).
  6. D. J. Baker and G. J. Romick, “The rayleigh: interpretation of the unit in terms of column emission rate or apparent radiance expressed in SI units,” Appl. Opt.15(8), 1966–1968 (1976).
    [CrossRef] [PubMed]
  7. D. A. Landgrebe, Signal Theory Methods in Multispectral Remote Sensing (Wiley, 2003).

2007

2000

1991

P. J. Miller, “Use of tunable liquid crystal filters to link radiometric and photometric standards,” Metrologia28(3), 145–149 (1991).
[CrossRef]

1976

Baker, D. J.

Chernous, S. A.

Deehr, C. S.

Dyrland, M.

Heia, K.

Holmes, J. M.

Lorentzen, D. A.

Miller, P. J.

P. J. Miller, “Use of tunable liquid crystal filters to link radiometric and photometric standards,” Metrologia28(3), 145–149 (1991).
[CrossRef]

Moen, J.

Romick, G. J.

Sigernes, F.

Svenøe, T.

Svinyu, T.

Appl. Opt.

J. Opt. Technol.

Metrologia

P. J. Miller, “Use of tunable liquid crystal filters to link radiometric and photometric standards,” Metrologia28(3), 145–149 (1991).
[CrossRef]

Other

R. Nakatsuji, PerkinElmer - Caliper Life Sciences, 68 Elm St., Hopkinton, MA 01748, USA (personal communication, 2012).

D. A. Landgrebe, Signal Theory Methods in Multispectral Remote Sensing (Wiley, 2003).

W. L. Wolfe, Introduction to Imaging Spectrometers (SPIE Press, 1997).

Supplementary Material (3)

» Media 1: MPG (3087 KB)     
» Media 2: MPG (3218 KB)     
» Media 3: AVI (4072 KB)     

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Figures (8)

Fig. 1
Fig. 1

Lens mechanics and optical diagram of the NORUSCA II all-sky lens: (1) focusing mechanism and collimator lenses, (2) filter box - chamber, (3) camera lens, and (4) camera head.

Fig. 2
Fig. 2

Two NORUSCA II 1st Generation all-sky cameras (A) and (B). (1) Front element of all-sky lens, (2) 24 x 4 inch2 mount plate, (3) collimator lens tube, (4) lens mount, (5) ring holders, (6) LCTF filter box, (7) camera lens, and (8) EMCCD detector. Instrumental volume is ~65 x 18 x 16 cm3. Total mass is 8.9 kg.

Fig. 3
Fig. 3

Calculated Polychromatic Line Spread Function (LSF) of the NORUSCA II all sky lens as a function of view angle to the optical axis.

Fig. 4
Fig. 4

Mapping function of the NORUSCA II all-sky lens at wavelength 557.7 nm. Square symbols are the position displacements of the pinhole from image center as a function of view angle. The solid black line is a 2nd order polynomial fit to the data. Colored solid lines are different standard fisheye mapping functions. The blue, green, red and yellow solid lines represent linear scaled, orthographic, equal area and stereographic fisheye mapping functions, respectively.

Fig. 5
Fig. 5

The NORUSCA II camera on-optical axis center pixel spectral raw data. The spectra, Cλ, (blue solid curve) is a 3rd order polynomial fit to the raw data (blue dots). The standard deviation of the raw counts is ± 376 counts. The source is a Lambertian surface (Labsphere SRT-99-180) illuminated by 45W tungsten lamp (ORIEL SN7-1633) at a distance of z = 8 m. The black spectrum, Kλ, is the calibration factors in units of R s CTS−1. The red spectrum is from a mercury vapor tube supplied by Edmund Optics Ltd (SN K60908). Exposure time is 100 ms. Gain is 100.

Fig. 6
Fig. 6

Raw data sample from the NORUSCA II camera 24th of January 2012 at 15:15:03UT. Location is the Kjell Henriksen Observatory (KHO). Panel (A): Image taken at center wavelength λ = 557.7 nm with exposure time 1 second and gain equal 100. North is ~28 degrees clockwise from the vertical with East to the right. The image is scaled down to 8-bit from 0 to 30846 CTS/s. Panel (B): 64 x.64 pixels zoom-window of the planet Jupiter. Panel (C): Vertical scatter plot of image in panel (B).

Fig. 7
Fig. 7

. Panel (A): Color composite image from the NORUSCA II camera 24th of January 2012 at 15:15 UT. Location is the Kjell Henriksen Observatory (KHO). The Red color component of the image is at center wavelength 630 nm, Green at 557.7 nm and Blue at 470.9 nm. The color scaled bars to the right are in units of CTS/s. The exposure time is 1 second and the gain is 100 for all channels. Panel (B): Color composite from 17:30 UT. Red arrow points to unidentified low intensity wave pattern. Blue arrow points to the Milky Way. Animated RGB sequence from 15:00 to 18:30 UT (Media 1).

Fig. 8
Fig. 8

Panel (A): Color composite image from the NORUSCA II camera 29th of December 2011 at 08:55:00UT. Location is the Kjell Henriksen Observatory (KHO). The Red color component of the image is at center wavelength 630 nm, Green at 557.7 nm and Blue at 470.9 nm. The color scaled bars to the right are in units of CTS/s. The exposure time is 1 second and the gain is 100. A rapid playback of the whole event from 06:00 to 09:40 UT is shown in (Media 2). Panel (B) shows the results of a supervised classification using all 15 channels of the instrument. See (Media 3) for spectral movie. Classes: (1) Scattered sun and moon light, (2) Reflected light from Breinosa (snow surface), (3) Auroral green belt emissions, (4) Discrete green auroral arcs, (5) Diffuse red aurora, and (6-7) Sky background.

Tables (3)

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Table 1 Technical characteristics of the NORUSCA II all-sky lens

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Table 2 Map function coefficients of NORUSCA II all-sky lens used in Eq. (1).

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Table 3 NORUSCA II auroral channels.

Equations (4)

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R A 0 + A 1 ×θ+ A 2 × θ 2 ,[mmorPIXELS]
M λ = B λ × ρ λ × ( z 0 z ) 2 ,[mW m 2 n m 1 ]
FWHM=B P λ λ 8 .[nm]
K λ = M λ × C λ 1 ×B P λ [RsCT S 1 ]

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