Progress in BRDF calibration measurements in the SWIR

Abstract

Satellite instruments operating in the reflective solar wavelength region often require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF). Laboratory-based diffusers are used in their pre-flight calibrations and at ground-based support of on-orbit remote sensing instruments. The Diffuser Calibration Lab at NASA's Goddard Space Flight Center is a secondary diffuser calibration standard after NIST for over two decades, providing numerous NASA projects with BRDF data in the UV, Visible and the NIR spectral regions. The Diffuser Calibration Lab works on extending the covered spectral range from 900 nm up to 1.7 microns. The measurements are made using the existing scatterometer by replacing the Si photodiode based receiver with an InGaAs-based one. The BRDF data was recorded at normal incidence and scatter zenith angles from 10 to 60 deg. Tunable coherent light source was used at this setup. Monochromator based broadband light source application is also under development. The results are discussed and compared to empirically generated BRDF data from simple model based on 6 deg directional/hemispherical measurements and experimental data in the 900 - 1100 nm spectral range.