ISIS-II Scanning Auroral Photometer

C. D. Anger; T. Fancott; J. McNally; H. S. Kerr

doi:10.1364/AO.12.001753

Applied Optics
Vol. 12,
Issue 8,
pp. 1753-1766
(1973)
•https://doi.org/10.1364/AO.12.001753

ISIS-II Scanning Auroral Photometer

C. D. Anger, T. Fancott, J. McNally, and H. S. Kerr

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C. D. Anger, T. Fancott, J. McNally, and H. S. Kerr, "ISIS-II Scanning Auroral Photometer," Appl. Opt. 12, 1753-1766 (1973)

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Abstract

The ISIS-II dual wavelength scanning auroral photometer is designed to map the distribution of auroral emissions at 5577 Å and 3914 Å over the portion of the dark earth visible to the spacecraft. A combination of internal electronic scanning and the natural orbital and rotational motions of the spacecraft causes a dual wavelength photometer to be scanned systematically across the earth. The data will be reproduced directly in the form of separate pictures representing emissions at each wavelength, which will be used to study the large-scale distribution and morphology of auroras, to study the ratio of 3914-Å and 5577-Å emissions (thought to depend upon the energies of exciting particles), and to compare with results from other instruments on board the spacecraft and on the ground. The Red Line Photometer experiment on the same spacecraft is described in an accompanying paper by Shepherd, et al.. [ Appl. Opt. 12, 1767 ( 1973)]. The instrument can be thought of as the photometric equivalent of an all-sky color camera which will view the aurora from above instead of below and with a much wider vantage point unobstructed by cloud and haze. In one satellite pass, the instrument will be capable of surveying (in one hemisphere) the entire polar region in which auroras normally occur.

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Subject	Tests done	Conclusions
Optical Materials:
Effects of radiation	Radiated glass and quartz samples	Use ultrapure quartz for optical components (except for glass window on PMT). Enclose glass-envelope calibration lamps in tungsten housings.
Scintillation effects from ionizing particles	Study only	Do not use sapphire. Small effective photocathode area will minimize scintillation pulse rate. Interference should not be serious.
Light scattering properties	Measured total hemisphere scattering of sample materials	Fused materials superior to single-crystal materials. Scattering from fused silica lens will be negligible compared to interference filter scattering.
Interference Filters:
Temperature variation of characteristics	Measured filter wavelength response at different temperatures	Only minor variation observed in transmission and bandpass of Thin Films Inc. all-dielectric filters constructed on ultra-pure quartz substrates. Variation of center-wavelength: +0.13 Å per °C at 3914 Å, +0.21 Å per °C at 5577 Å, +0.23 Å per °C at 6300 Å.
Effects of radiation	Radiated sample filters	For 10⁷ rads, transmission of 6300-Å all-dielectric filter (100 Å FWHM) had increased to 42% (was 34%); 6300-Å narrow band filter characteristics unchanged at 10⁷ rads; 5577 filter transmission dropped 3%; 3914 filter transmission unchanged at 10⁶ rads but dropped from 24% to 19% by 10⁷ rads, due mainly to increased absorption of epoxy cement used to hold filter together. Conventional filters with colored-glass blockers at 5577 Å showed drop to 0.7 of previous peak transmission at 10⁵ rads and 0.24 of peak at 10⁶ rads; at 3914-Å peak dropped to 0.6 at 10⁵ rads and 0.13 at 10⁶. Cleaved mica interference 5900-Å filter (unblocked) was unchanged in transmission at 10⁷ rads.
Light scattering properties	Measured component of light transmitted through filter that had been scattered out of collimated beam	Scattered transmitted component was 10–20% of unscattered component, some of it coming out through edges-of filter. The portion of scattered transmitted light at wavelengths outside the filter bandpass was negligible.
Baffle material and surface preparation	Measured total hemispheric reflectance of several sample surfaces (space approved materials)	Best was 2.8% (normal incidence) for 3M Matte Black Velvet brushed on 6061 aluminum
	Measured baffle scattering for several sample edges with different surface treatments (same as above)	If we say that the baffle edge is replaced by a 100% transmitting Lambertian surface of equal length and of width k such that the same scattered flux results at an angle α with respect to the incident beam, the best baffle edge (also Black Velvet) gave a value for k of 8 ± 4 × 10⁻⁶ m for 15° < α < 90°.

Diameter of aperture (where α is nominal diameter for 0.4 degree acceptance angle)		0.5α	1.0α	1.5α	2.0α	2.5α	3.0α
Response for two-dimensional Gaussian with 1/e value at distance α from central max (desired response		0.78	0.37	0.11	0.02	0.002	~0
Distance between rear surface of lens and aperture (inches)
Marginal focus	3.48	0.95	0.83	0.71	0.57	0.42	0
“Best focus”	3.56	0.81	0.60	0.40	0	0	0
Best approx. to Gaussian	3.60	0.82	0.53	0.15	0.05	0	0
	3.70	0.65	0.40	0.32	0.32	0.23	0.15
Paraxial focus	3.82	0.82	0.67	0.61	0.55	0.47	0.40
		Percentage of energy outside aperture

Sampling interval^a	Total distortion^b %
0.67	0.15
0.83	1
1.00	6
1.17	10
1.33	19
1.50	28
1.67	35

Subject	Tests done	Conclusions
Optical Materials:
Effects of radiation	Radiated glass and quartz samples	Use ultrapure quartz for optical components (except for glass window on PMT). Enclose glass-envelope calibration lamps in tungsten housings.
Scintillation effects from ionizing particles	Study only	Do not use sapphire. Small effective photocathode area will minimize scintillation pulse rate. Interference should not be serious.
Light scattering properties	Measured total hemisphere scattering of sample materials	Fused materials superior to single-crystal materials. Scattering from fused silica lens will be negligible compared to interference filter scattering.
Interference Filters:
Temperature variation of characteristics	Measured filter wavelength response at different temperatures	Only minor variation observed in transmission and bandpass of Thin Films Inc. all-dielectric filters constructed on ultra-pure quartz substrates. Variation of center-wavelength: +0.13 Å per °C at 3914 Å, +0.21 Å per °C at 5577 Å, +0.23 Å per °C at 6300 Å.
Effects of radiation	Radiated sample filters	For 10⁷ rads, transmission of 6300-Å all-dielectric filter (100 Å FWHM) had increased to 42% (was 34%); 6300-Å narrow band filter characteristics unchanged at 10⁷ rads; 5577 filter transmission dropped 3%; 3914 filter transmission unchanged at 10⁶ rads but dropped from 24% to 19% by 10⁷ rads, due mainly to increased absorption of epoxy cement used to hold filter together. Conventional filters with colored-glass blockers at 5577 Å showed drop to 0.7 of previous peak transmission at 10⁵ rads and 0.24 of peak at 10⁶ rads; at 3914-Å peak dropped to 0.6 at 10⁵ rads and 0.13 at 10⁶. Cleaved mica interference 5900-Å filter (unblocked) was unchanged in transmission at 10⁷ rads.
Light scattering properties	Measured component of light transmitted through filter that had been scattered out of collimated beam	Scattered transmitted component was 10–20% of unscattered component, some of it coming out through edges-of filter. The portion of scattered transmitted light at wavelengths outside the filter bandpass was negligible.
Baffle material and surface preparation	Measured total hemispheric reflectance of several sample surfaces (space approved materials)	Best was 2.8% (normal incidence) for 3M Matte Black Velvet brushed on 6061 aluminum
	Measured baffle scattering for several sample edges with different surface treatments (same as above)	If we say that the baffle edge is replaced by a 100% transmitting Lambertian surface of equal length and of width k such that the same scattered flux results at an angle α with respect to the incident beam, the best baffle edge (also Black Velvet) gave a value for k of 8 ± 4 × 10⁻⁶ m for 15° < α < 90°.

Diameter of aperture (where α is nominal diameter for 0.4 degree acceptance angle)		0.5α	1.0α	1.5α	2.0α	2.5α	3.0α
Response for two-dimensional Gaussian with 1/e value at distance α from central max (desired response		0.78	0.37	0.11	0.02	0.002	~0
Distance between rear surface of lens and aperture (inches)
Marginal focus	3.48	0.95	0.83	0.71	0.57	0.42	0
“Best focus”	3.56	0.81	0.60	0.40	0	0	0
Best approx. to Gaussian	3.60	0.82	0.53	0.15	0.05	0	0
	3.70	0.65	0.40	0.32	0.32	0.23	0.15
Paraxial focus	3.82	0.82	0.67	0.61	0.55	0.47	0.40
		Percentage of energy outside aperture

Abstract

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Figures (5)

Tables (3)

Equations (3)

Applied Optics