FIGIFIGO An Advanced Portable System for Spectropolarimetry Teemu
FIGIFIGO: An Advanced Portable System for Spectropolarimetry Teemu 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 2
Operation • 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) 3
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 4
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 5
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 6
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 7
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 8
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 9
Software • Custom Lab. View measurement software • Handles the measurement sequence, instrument communication, raw data storage • Matlab post processing software 10
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 11
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