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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