Sensitivity Calibration of Narrow Field of View Optical Instruments F. Sigernes 1, T. Svenøe 2, J. Holmes 1, M. Dyrland 1, D.A. Lorentzen 1, J. Moen 3, 1, S. Chernouss 4, and C. S. Deehr 5 1 The University Center in Svalbard (UNIS), N-9171 Longyearbyen, Norway. 2 The Norwegian Polar Institute, Ny-Ålesund, Norway 3 Institute of Physics, University of Oslo, Norway 4 Polar Geophysical Institute, Apatity, Russia 5 Geophysical Institute, University of Alaska, Fairbanks, USA

BACKGROUND The increasing number of low light level optical instruments operated in Svalbard (Longyearbyen, Barentsburg and Ny-Ålesund) for monitoring auroras and airglow phenomena emphasizes the need for establishing accurate calibration routines of international standard. CONTENT 1.THEORETICAL BASIS 2.EXPERIMENTAL SETUP AT UNIS 3.TRANSFER OF LAMP CERTIFICATE 4.SCREEN BRIGHTNESS CONTROL

1. THEORETICAL BASIS a) Lambertian surface Lambert’s Cosine law Total hemispherical emission rate b) Calibration setup Irradiance certificate Entering emission rate Reemitted radiation Then Radiance towards instrument becomes Since inverse square law is The generalized RayleighExitance of screen

(1) 18 x 18 inch2 Lambertian surface, (2) rails, (3) adjustable mobile table, (4) entrance fiber to spectrograph, (5) door with baffle, (6) room lights, (7) tungsten lamp, (8) power cable to lamp filament. 2. THE UNIS LABORATORY

Fixed Imaging Compact Spectrograph (FICS SN 7743): (A) concave holographic grating, (B) flat mirror, (C) detector (CCD), (D) fiber bundle, (E) entrance slit (A) THE FICS SPECTROGRAPH 2. THE UNIS LABORATORY (B) WAVELENGTH CALIBRATION Low pressure mercury pen lamp Mercury vapour tube Fluorescent tube CoefficientsConstants a x a x 10 0 a x Range 2560 – Å; FWHM ~ 80Å

3. RESULTS TRANSFER OF LAMP CERTIFICATE CERTIFIED 1000W TUNGSTEN ORIEL SN NIST TRACABLE SECONDARY STANDARD 200W TUNGSTEN (FRED01) KEY PARAMETERS: Exposure time 160 msec z = 8.56 m Filter: BK-7 FUNCTIONAL FIT (DOTTED LINE): a = 73.9 and b =

3. RESULTS SCREEN BRIGHTNESS CONTROL KEY PARAMETERS: Secondary 200W Tungsten Exposure time 160 msec z = 8.56 m Filter: BK-7 Distance increments = 0.5 m

4. CONCLUDING REMARKS So far: The optical laboratory at UNIS is constructed according to basic Lambertian theory to calibrate narrow field of view low light level optical instruments. Secondary certification of a 200W Tungsten lamp has been conducted in the visible part of the spectrum (4000 – 8000 Å). A procedure to control screen brightness without change in spectral shape by varying the screen-lamp distance from 8 down to 3.5m has been demonstrated in the kR/Å range of the visible spectrum. Future: A low power tungsten lamp is needed to calibrate below 1kR. Secondary certification above 8000 Å requires appropriate cut- off filters. A new monochromatic is installed and ready for use as source to calibrate filters instruments. …