Abstract
We report the development of a table-top goniometer at GSFC, NASA, and the preliminary results of solar diffuser BRDF measurements for satellite instrumentation in the reflective solar bands. The table-top goniometer is able to conduct both in-plane and out-of-plane BRDF measurements, which was built up using commercial stages and opto-mechanics to minimize the need for extensive machining. Various light sources with the power stabilities of < 0.5 % cover the 300 nm to 2500 nm wavelength region. These include a laser diode driven plasma broadband light source, such as a Xe lamp, a supercontinuum laser, and single wavelength lasers. The broadband sources can be used either with dispersive elements to generate monochromatic light, or as built. Si and extended InGaAs detectors cover the spectral range from 300 nm to 2500 nm and are used in absolute and relative BRDF measurements. Two mini-spectrometers operating in the UV-NIR and NIR-SWIR measure the spectra of scattered light from the broadband sources in a measurement of relative BRDF. Two NIST traceable Spectralon standard samples, a white diffuser and black diffuser, are used to validate the system and to make comparison measurements. We present the spectral coverage of light sources and their stabilities, the detector linearities, and signal to noise ratios. The BRDF results at specific wavelengths are also shown in the different configurations to verify the BRDF reciprocity of diffuser at the angles of interest. We also present the methodology of how to complete the BRDF measurements beyond the spectral and angular coverage of NIST traceable standards. The uncertainty budget of BRDF measurements will also be discussed.
Preliminary Results of Solar Diffuser BRDF Measurements Using a Table-Top Goniometer at NASA GSFC
We report the development of a table-top goniometer at GSFC, NASA, and the preliminary results of solar diffuser BRDF measurements for satellite instrumentation in the reflective solar bands. The table-top goniometer is able to conduct both in-plane and out-of-plane BRDF measurements, which was built up using commercial stages and opto-mechanics to minimize the need for extensive machining. Various light sources with the power stabilities of < 0.5 % cover the 300 nm to 2500 nm wavelength region. These include a laser diode driven plasma broadband light source, such as a Xe lamp, a supercontinuum laser, and single wavelength lasers. The broadband sources can be used either with dispersive elements to generate monochromatic light, or as built. Si and extended InGaAs detectors cover the spectral range from 300 nm to 2500 nm and are used in absolute and relative BRDF measurements. Two mini-spectrometers operating in the UV-NIR and NIR-SWIR measure the spectra of scattered light from the broadband sources in a measurement of relative BRDF. Two NIST traceable Spectralon standard samples, a white diffuser and black diffuser, are used to validate the system and to make comparison measurements. We present the spectral coverage of light sources and their stabilities, the detector linearities, and signal to noise ratios. The BRDF results at specific wavelengths are also shown in the different configurations to verify the BRDF reciprocity of diffuser at the angles of interest. We also present the methodology of how to complete the BRDF measurements beyond the spectral and angular coverage of NIST traceable standards. The uncertainty budget of BRDF measurements will also be discussed.