Abstract

To investigate the dynamics of auroras and faint upper atmospheric emissions, a new type of imaging instrument was developed. The instrument is a wide field of view, narrow-spectral-band imaging system using an intensified S.E.C. TV camera in a time exposure mode. Pictures were taken at very low light levels of a few photons per exposure per resolution element. These pictures are displayed in the form of a pseudocolor presentation in which the color represents spectral ratios of two of the observed auroral spectral emission features. The spectral ratios play an important part in the interpretation of auroral particle dynamics. A digital picture processing facility is also part of the system which enables the digital manppulation of the pictures at standard TV rates. As an example, hydrogen auroras can be displayed having been corrected for nonspectral background by subtracting a picture obtained by a suitable background filter. The instrumentation was calibrated in the laboratory and was used in several field experiments. Elaborate exposure sequences were developed to extend the dynamic range and to cover the large range of auroral brightnesses in a fairly linear manner.

© 1977 Optical Society of America

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References

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  1. C. P. Pike, J. A. Whalen, J. Geophys. Res. 79, 985 (1974).
    [CrossRef]
  2. M. M. Rees, R. A. Jones, Planet Space Sci. 21, 1213 (1973).
    [CrossRef]
  3. M. H. Rees, D. Luckey, J. Geophys. Res. 78, 8391 (1973).
    [CrossRef]
  4. R. H. Eather, S. B. Mende, R. J. R. Judge, Accepted by J. Geophys. Res. (1976).
  5. R. H. Eather, S. B. Mende, “High Latitude Particle Precipitation and Source Regions in the Magnetosphere,” in Ionosphere-Magnetosphere InteractionsK. Folkestad, Ed. (U. Oslo Press, Oslo, 1972b), pp. 139–154.
  6. R. H. Eather, S. B. Mende, J. Geophys. Res. 77, 660 (1972).
    [CrossRef]
  7. R. H. Eather, Rev. Geophys. 5, 207 (1962).
    [CrossRef]
  8. R. H. Eather, D. L. Reasoner, Appl. Opt. 8, 227 (1969).
    [CrossRef] [PubMed]
  9. R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
    [CrossRef]
  10. T. F. Bell, J. Geophys. Res. 81, 3316 (1976).
    [CrossRef]
  11. S. B. Mende, K. H. Eather, J. Geophys. Res. 81, 3771 (1976).
    [CrossRef]
  12. S. B. Mende, Appl. Opt. 10, 829 (1971).
    [CrossRef] [PubMed]
  13. E. K. Aamodt, S. B. Mende, “Image Processor for the Reduction of Scientific TV Data,” to be published (1976).

1976 (2)

T. F. Bell, J. Geophys. Res. 81, 3316 (1976).
[CrossRef]

S. B. Mende, K. H. Eather, J. Geophys. Res. 81, 3771 (1976).
[CrossRef]

1974 (1)

C. P. Pike, J. A. Whalen, J. Geophys. Res. 79, 985 (1974).
[CrossRef]

1973 (2)

M. M. Rees, R. A. Jones, Planet Space Sci. 21, 1213 (1973).
[CrossRef]

M. H. Rees, D. Luckey, J. Geophys. Res. 78, 8391 (1973).
[CrossRef]

1972 (1)

R. H. Eather, S. B. Mende, J. Geophys. Res. 77, 660 (1972).
[CrossRef]

1971 (1)

1969 (1)

1964 (1)

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

1962 (1)

R. H. Eather, Rev. Geophys. 5, 207 (1962).
[CrossRef]

Aamodt, E. K.

E. K. Aamodt, S. B. Mende, “Image Processor for the Reduction of Scientific TV Data,” to be published (1976).

Bell, T. F.

T. F. Bell, J. Geophys. Res. 81, 3316 (1976).
[CrossRef]

Eather, K. H.

S. B. Mende, K. H. Eather, J. Geophys. Res. 81, 3771 (1976).
[CrossRef]

Eather, R. H.

R. H. Eather, S. B. Mende, J. Geophys. Res. 77, 660 (1972).
[CrossRef]

R. H. Eather, D. L. Reasoner, Appl. Opt. 8, 227 (1969).
[CrossRef] [PubMed]

R. H. Eather, Rev. Geophys. 5, 207 (1962).
[CrossRef]

R. H. Eather, S. B. Mende, R. J. R. Judge, Accepted by J. Geophys. Res. (1976).

R. H. Eather, S. B. Mende, “High Latitude Particle Precipitation and Source Regions in the Magnetosphere,” in Ionosphere-Magnetosphere InteractionsK. Folkestad, Ed. (U. Oslo Press, Oslo, 1972b), pp. 139–154.

Filby, R. S.

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

Jones, R. A.

M. M. Rees, R. A. Jones, Planet Space Sci. 21, 1213 (1973).
[CrossRef]

Judge, R. J. R.

R. H. Eather, S. B. Mende, R. J. R. Judge, Accepted by J. Geophys. Res. (1976).

Luckey, D.

M. H. Rees, D. Luckey, J. Geophys. Res. 78, 8391 (1973).
[CrossRef]

Mende, S. B.

S. B. Mende, K. H. Eather, J. Geophys. Res. 81, 3771 (1976).
[CrossRef]

R. H. Eather, S. B. Mende, J. Geophys. Res. 77, 660 (1972).
[CrossRef]

S. B. Mende, Appl. Opt. 10, 829 (1971).
[CrossRef] [PubMed]

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

R. H. Eather, S. B. Mende, “High Latitude Particle Precipitation and Source Regions in the Magnetosphere,” in Ionosphere-Magnetosphere InteractionsK. Folkestad, Ed. (U. Oslo Press, Oslo, 1972b), pp. 139–154.

E. K. Aamodt, S. B. Mende, “Image Processor for the Reduction of Scientific TV Data,” to be published (1976).

R. H. Eather, S. B. Mende, R. J. R. Judge, Accepted by J. Geophys. Res. (1976).

Pike, C. P.

C. P. Pike, J. A. Whalen, J. Geophys. Res. 79, 985 (1974).
[CrossRef]

Reasoner, D. L.

Rees, M. H.

M. H. Rees, D. Luckey, J. Geophys. Res. 78, 8391 (1973).
[CrossRef]

Rees, M. M.

M. M. Rees, R. A. Jones, Planet Space Sci. 21, 1213 (1973).
[CrossRef]

Rosenbloom, M. E.

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

Twiddy, N. D.

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

Whalen, J. A.

C. P. Pike, J. A. Whalen, J. Geophys. Res. 79, 985 (1974).
[CrossRef]

Appl. Opt. (2)

J. Geophys. Res. (5)

C. P. Pike, J. A. Whalen, J. Geophys. Res. 79, 985 (1974).
[CrossRef]

M. H. Rees, D. Luckey, J. Geophys. Res. 78, 8391 (1973).
[CrossRef]

R. H. Eather, S. B. Mende, J. Geophys. Res. 77, 660 (1972).
[CrossRef]

T. F. Bell, J. Geophys. Res. 81, 3316 (1976).
[CrossRef]

S. B. Mende, K. H. Eather, J. Geophys. Res. 81, 3771 (1976).
[CrossRef]

Nature (1)

R. S. Filby, S. B. Mende, M. E. Rosenbloom, N. D. Twiddy, Nature 201, 801 (1964).
[CrossRef]

Planet Space Sci. (1)

M. M. Rees, R. A. Jones, Planet Space Sci. 21, 1213 (1973).
[CrossRef]

Rev. Geophys. (1)

R. H. Eather, Rev. Geophys. 5, 207 (1962).
[CrossRef]

Other (3)

E. K. Aamodt, S. B. Mende, “Image Processor for the Reduction of Scientific TV Data,” to be published (1976).

R. H. Eather, S. B. Mende, R. J. R. Judge, Accepted by J. Geophys. Res. (1976).

R. H. Eather, S. B. Mende, “High Latitude Particle Precipitation and Source Regions in the Magnetosphere,” in Ionosphere-Magnetosphere InteractionsK. Folkestad, Ed. (U. Oslo Press, Oslo, 1972b), pp. 139–154.

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Figures (9)

Fig. 1
Fig. 1

(a) Simple lens telecentric imager with filter. At an arbitrary point A in the plane of the aperture the ray passing through at an angle θ is brought to focus at point 1. This may subtend angle φ′ with the optic axis at focus It can be shown that this angle φ′ is independent of θ and that it is the same for any image point 1. This is because the aperture is also one focal length distant from the lens, all rays passing through A are parallel at the other side of the lens, and thus they all subtend the same angle φ′ with respect to the optic axis. Such angle φ′ can be Found for all points A in the aperture plane provided the aperture is smaller than the lens permitting the extreme rays (θmax) through the lens. (b) Schematic configuration of telecentric all-sky lens. Meniscus field widener forms virtual image of the sky. Doublet forms a large 7.6-cm (3-in.) intermediate image shown inside the filter. The telecentric lens is exactly one focal length f in front of the aperture of doublet, thus satisfying the telecentric condition. The camera lens forms a small 2.54-cm (1-in.) image on the intensifier photocathode. The condenser lens behind the filter ensures that all the light is directed toward the camera lens.

Fig. 2
Fig. 2

System diagram. The optics focuses the image on the photocathode of the image intensified TV camera. Time exposures, the filter wheel position, and the functioning of the video signal processing system are controlled by CPU. The signal processor consists of the Real Time Image Processor (R.T.I.P.), a three-channel video storage disk, and monitors including an one color (RGB) monitor. The real time video processor R.T.I.P. provides the facility of adding or subtracting consecutive TV frames for differencing of pictures or for SNR enhancement by means of picture averaging.

Fig. 3
Fig. 3

Superposition of the camera head above and the rack mounted control equipment below as it was set up in Kiruna, Sweden.

Fig. 4
Fig. 4

(a) A TV line as shown on an oscilloscope through two light sources, which are 600 R and 150 R. The 600-R light source is strongly saturating. (b) Same as (a) except the left light source is 6.5 kR. Note the lateral spread of the image.

Fig. 5
Fig. 5

Composite calibration curve. The curve represented by L, M, and S stands for sixty-four (~1-sec), eight (~⅛-sec), and one TV field (1/60-sec) exposures, respectively. The video output is multiplied by 8 for M and 64 for S.

Fig. 6
Fig. 6

Linearity with angle. The calibration curve of the geometrical fidelity of the system. Zenith angle (from vertical) is shown against radial distance from center as a fraction of the total field of view. On the right-hand scale the number of geographical degrees is shown as a function of zenith angle for auroral λ4278 Å (B, at ≈110-km altitude) and for aurora λ6300 Å (R, at ≈180-km altitude).

Fig. 7
Fig. 7

Computer generated plots of the distance (L value) of the equatorial crossing of the magnetic field line in the field of view at Kiruna, Sweden. This distance is expressed in earth radii: (a) 110-km constant altitude; (b) 180-km constant altitude. The IGRF internal model was used for computing the magnetic field lines.

Fig. 8
Fig. 8

Example of quiescent multiple auroral arc structure. Date and time encoded by character generators. Binary identification bars on the left of the picture are used to synchronize and identify data from video tape. The standard light source is displayed at top right of frame.

Fig. 9
Fig. 9

(a) Example of hydrogen β (4861) aurora through 25-Å filter. (b) Example of control filter of 25 Å (4816) taken a few seconds after hydrogen β shown in Fig. 9(a). The difference picture is generated by subtracting the video signal showing the corrected pure contribution of the Hβ (proton) aurorae. The electron aurora is largely canceled by subtraction.

Tables (1)

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Table I Exposure Durations for the All-Sky Imaging Photometer

Equations (8)

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( δ λ ) / λ = - [ ( θ 2 ) / ( 2 μ 2 ) ] ,
Δ λ ¯ = λ | θ 2 ¯ 2 μ 2 | = λ θ max 2 4 μ 2
Δ λ max = λ θ max 2 2 μ 2 .
Δ λ ¯ = ½ Δ λ max .
I p = 10 6 T D 2 α 2 π 16 photons R - 1 sec - 1 ,
α = μ 2 [ ( δ λ f ) / λ ] 1 / 2 ,
I p = 10 6 T D 2 δ λ f μ 2 π 16 λ photons R - 1 sec - 1 .
α μ [ ( δ λ ) / λ ] 1 / 2 = 0.145 rad ( 8.3° ) for μ = 1.5 , = 0.183 rad ( 10.5° ) for μ = 1.9 ,

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