Angular and seasonal variation of spectral surface reflectance ratios: implications for the remote sensing of aerosol over land

• Published in: IEEE transactions on geoscience and remote sensing Vol. 39; no. 2; pp. 275 - 283
• Main Authors: Remer, L.A., Wald, A.E., Kaufman, Y.J.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2001; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aerosols; Aircraft; Algorithms; Applied geophysics; Atmospheric aerosols; Clouds; Earth sciences; Earth, ocean, space; Estimating; Exact sciences and technology; Ice; Internal geophysics; Land; Land surface; Optical reflection; Optical surface waves; Reflectance; Reflectivity; Remote sensing; Spectroscopy; Specular reflection; Surface waves; Testing; Vegetation; wavelength; algorithms; airborne methods; aerosols; thickness; reflectance; spectroscopy; remote sensing; vegetation; seasonal variations; errors; direction
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/36.905235

We obtain valuable information on the angular and seasonal variability of surface reflectance using a hand-held spectrometer from a light aircraft. The data is used to test a procedure that allows us to estimate visible surface reflectance from the longer wavelength 2.1 /spl mu/m channel (mid-IR). Estimating or avoiding surface reflectance in the visible is a vital first step in most algorithms that retrieve aerosol optical thickness over land targets. The data indicate that specular reflection found when viewing targets from the forward direction can severely corrupt the relationships between the visible and 2.1 /spl mu/m reflectance that were derived from nadir data. There is a month by month variation in the ratios between the visible and the mid-IR, weakly correlated to the Normalized Difference Vegetation Index (NDVI). If specular reflection is not avoided, the errors resulting from estimating surface reflectance from the mid-IR exceed the acceptable limit of /spl Delta//spl rho//spl sim/0.01 in roughly 40% of the cases, using the current algorithm. This is reduced to 25% of the cases if specular reflection is avoided.