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BASIC HYPER SPECTRAL IMAGING 

This lecture focuses on the sensitivity calibration of low light level optical instruments in Svalbard, emphasizing the need for accurate calibration routines using international standards. It covers the experimental setup, theoretical basis, transfer of lamp certificate, and screen brightness control.

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BASIC HYPER SPECTRAL IMAGING 

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  1. BASIC HYPER SPECTRAL IMAGING  Fred Sigernes 1,2,3,4 1 The University Centre in Svalbard (UNIS), N-9171 Longyearbyen, Norway 2 The Birkeland Centre for Space Science (BCSS) 3 The Kjell Henriksen Observatory (KHO) 4 Centre for Autonomous Marine Operations and Systems (AMOS) NTNU Lectures: TTK20 Hyperspectral remote sensing, Module 1, AMOS – NTNU, 11-13 September, 2018.

  2. Lecture plan: TTK20 Hyperspectral remote sensing Module 1 Instructor: Adjunct Professor Fred Sigernes Lectures: TTK20 Hyperspectral remote sensing, Module 1, AMOS – NTNU, 11-13 September, 2018.

  3. Sensitivity Calibration of Narrow Field of View Optical Instruments F. Sigernes1, 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

  4. 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 • EXPERIMENTAL SETUP AT UNIS • THEORETICAL BASIS • TRANSFER OF LAMP CERTIFICATE • SCREEN BRIGHTNESS CONTROL

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

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

  7. 2. THE UNIS LABORATORY (B) WAVELENGTH CALIBRATION (A) THE FICS SPECTROGRAPH Low pressure mercury pen lamp Mercury vapour tube Fluorescent tube Fixed Imaging Compact Spectrograph (FICS SN 7743): (A) concave holographic grating, (B) flat mirror, (C) detector (CCD), (D) fiber bundle, (E) entrance slit Range 2560 – 10945 Å; FWHM ~ 80Å

  8. 3. RESULTS TRANSFER OF LAMP CERTIFICATE CERTIFIED 1000W TUNGSTEN ORIEL SN7-1275 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 = 52568.

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

  10. 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 1 -132 kR/Å range of the visible spectrum. Future: • A low power 45W tungsten lamp is needed to calibrate below 1kR. • Secondary certification above 8000 Å requires appropriate cut-off filters. • A new monochromatic need to be installed and ready for use as source to calibrate filters instruments. • …

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