Abstract
The capability of making Bidirectional Scattering Distribution Function (BSDF) measurements on specular samples has been demonstrated using the Table-Top Goniometer (TTG) in the Diffuser Calibration Lab (DCL) at NASA GSFC. This capability has been used in the support of NASA satellite instrument programs. The TTG has also been used in the measurement of the BRDF of diffuse samples. In its current configuration using tunable laser sources, the TTG possesses the advantages of small incident beam profile and configuration flexibility to be able to meet the BSDF measurement requirements on specular samples with flat and curved surfaces. The TTG measurements are used in characterizing instrument straylight due to surface roughness and in determining the scattering light distribution function of optical surfaces. The BSDF measurements on specular samples are able to be performed over 8 orders of linear dynamic range corrected for instrument signature. In this presentation, we report BSDF results on two kinds of specular samples, a witness flat folder mirror for the NASA GSFC PACE project and four Multi-Layer Insulation (MLI) samples for the NASA GSFC Restore project. The BSDF measurements in the viewing angle range of ± 90° were acquired at 500 nm, 700 nm, and 2000 nm at incident angles of 0°, 8°, and 25° for the PACE sample, and at 500 nm, 633 nm, 700 nm, 900 nm, 1000 nm, 1550 nm, and 1800 nm at incident angles of 10° and 25° for the RESTORE samples. For both samples, the ABg model was applied for the BSDF data fitting to generate the parameters as inputs of optical modeling. The ABg model fitted the BSDF data from the polished surface of the flat mirror very well. However, two scattering components were seen in fitting the MLI BSDF results due to wrinkle and surface morphology issues. The Total Hemispherical Reflectance (THR) and Total Internal Scatter (TIS) measurements were also made on the samples and were compared to the BSDF results. The details of the specific BSDF measurement setup and the methodology for realization of the BRDF scale for specular samples are presented.
Specular BSDF Measurement Capability at NASA GSFC using a Table-Top Goniometer in Support of the Calibration of Remote Sensing Instruments
The capability of making Bidirectional Scattering Distribution Function (BSDF) measurements on specular samples has been demonstrated using the Table-Top Goniometer (TTG) in the Diffuser Calibration Lab (DCL) at NASA GSFC. This capability has been used in the support of NASA satellite instrument programs. The TTG has also been used in the measurement of the BRDF of diffuse samples. In its current configuration using tunable laser sources, the TTG possesses the advantages of small incident beam profile and configuration flexibility to be able to meet the BSDF measurement requirements on specular samples with flat and curved surfaces. The TTG measurements are used in characterizing instrument straylight due to surface roughness and in determining the scattering light distribution function of optical surfaces. The BSDF measurements on specular samples are able to be performed over 8 orders of linear dynamic range corrected for instrument signature. In this presentation, we report BSDF results on two kinds of specular samples, a witness flat folder mirror for the NASA GSFC PACE project and four Multi-Layer Insulation (MLI) samples for the NASA GSFC Restore project. The BSDF measurements in the viewing angle range of ± 90° were acquired at 500 nm, 700 nm, and 2000 nm at incident angles of 0°, 8°, and 25° for the PACE sample, and at 500 nm, 633 nm, 700 nm, 900 nm, 1000 nm, 1550 nm, and 1800 nm at incident angles of 10° and 25° for the RESTORE samples. For both samples, the ABg model was applied for the BSDF data fitting to generate the parameters as inputs of optical modeling. The ABg model fitted the BSDF data from the polished surface of the flat mirror very well. However, two scattering components were seen in fitting the MLI BSDF results due to wrinkle and surface morphology issues. The Total Hemispherical Reflectance (THR) and Total Internal Scatter (TIS) measurements were also made on the samples and were compared to the BSDF results. The details of the specific BSDF measurement setup and the methodology for realization of the BRDF scale for specular samples are presented.