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

Operation Main parts Target illuminated by Sun 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

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

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

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

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

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

Software Custom LabView measurement software Handles the measurement sequence, instrument communication, raw data storage Matlab post processing software

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