FIGIFIGO: An Advanced Portable System for Spectropolarimetry Teemu Hakala, Maria Gritsevich, Jouni...
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Transcript of FIGIFIGO: An Advanced Portable System for Spectropolarimetry Teemu Hakala, Maria Gritsevich, Jouni...
FIGIFIGO: An Advanced Portable System for SpectropolarimetryTeemu Hakala, Maria Gritsevich, Jouni Peltoniemi and Juha Suomalainen
FIGIFIGO
• Finnish Geodetic Institute Field Goniospectrometer
• A device for measuring directional properties of reflectance, Bidirectional Reflectance Factor (BRF)
• Design focused on field operation, but can also be used in laboratory
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Operation
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• Main parts• Measurement arm• Goniometer body
• Target illuminated by Sun• Light zenith and azimuth
• Measurement arm turns from side to side (view zenith)
• Goniometer body turned around the target (view azimuth)
Measurement
• Before each target measurement a reference panel (Spectralon) is measured
• The Spectralon and the target are also measured with direct illumination shadowed
• The target is measured with several (~6) view azimuth angles
• Total measurement time about 10-20 minutes
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Spectrometer
• ASD Field Spec Pro FR • 350-2500 nm spectral range• 3 nm FWHM @ 350-1000• 10 nm FWHM @ 1000-2500• 3 meter optical fiber
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Features (1)
• Measurement arm moved by a single motor • Arm angle (view zenith) measured with an electronic
inclinometer• View azimuth relative to Sun measured with a fisheye
camera mounted to the goniometer body• GPS position and time used to determine the light azimuth
and zenith angles• Level of incident irradiance measured with a broadband
(~300-1000 nm) pyranometer placed on a tripod• Used during post processing to compensate for minor changes in
illumination
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Features (2)
• Powered by 1-2 lead acid batteries • Several hours of measurement time
• Weight ~30-40 kg depending on how many batteries• Can be carried by two people for short distances, or easily moved
over snow
• Position of the measurement spot can be adjusted by a motorized mirror
• Used to compensate for the height displacement between arm motor axle and the sample surface
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Optics
• Possible to use a custom set of polarizing optics
• Linear polarizing Glan Thompson polarizer
• Usually measurement with four polarizer angles: 0°, 90°, 45° and 135°
• Measurement arm does four passes for each azimuth angle, one for each polarization
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Laboratory setup
• FIGIFIGO can be used in laborotory • Light source: 1000 W quarz tungsten halogen with
stabilized power source• Rotating ring used for more presice azimuth rotation of
FIGIFIGO• Light is collimated with an off axis parabolic mirror• A flat mirror for light zenith angle adjustment
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Software
• Custom LabView measurement software
• Handles the measurement sequence, instrument communication, raw data storage
• Matlab post processing software
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Thank you
• Suomalainen, J.; Hakala, T.; Peltoniemi, J.; Puttonen, E. Polarised Multiangular Reflectance Measurements Using the Finnish Geodetic Institute Field Goniospectrometer. Sensors 2009, 9, 3891-3907
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