The effect of anisotropic reflectance on imaging spectroscopy of snow properties
How does snow's anisotropic directional reflectance affect the mapping of snow properties from imaging spectrometer data? This sensitivity study applies two spectroscopy models to synthetic images of the spectral hemispherical–directional reflectance factor (HDRF) with prescribed snow-covered area and snow grain size.
Thomas H. Paintera and Jeff Dozierb
a Department of Geography and Institute for Computational Earth System Science University of California, Santa Barbara, CA 93106, USA
b Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106-5131, USA
Remote Sensing of Environment
Volume 89, Issue 4, 29 February 2004, Pages 409-422
Copyright © 2004 Elsevier Inc. All rights reserved.
Received 4 June 2003;
revised 19 September 2003;
accepted 30 September 2003. ;
Available online 17 January 2004.
Abstract
How does snow's anisotropic directional reflectance affect the mapping of snow properties from imaging spectrometer data? This sensitivity study applies two spectroscopy models to synthetic images of the spectral hemispherical–directional reflectance factor (HDRF) with prescribed snow-covered area and snow grain size. The MEMSCAG model determines both sub-pixel snow-covered area and the grain size of the fractional snow cover. The Nolin/Dozier model analyzes the ice absorption feature that spans wavelength λcongruent with1.03 μm to estimate snow grain radius when the pixel is fully snow-covered. Retrievals of subpixel snow-covered area with MEMSCAG are progressively more sensitive to the HDRF as grain size decreases, solar zenith angle increases, and fractional snow cover increases. The model overestimates snow cover in the forward reflectance angles by up to +20% and underestimates it in the backward reflectance angles by as much as −15%. Grain size retrievals from both MEMSCAG and Nolin/Dozier are more sensitive to anisotropy as grain size and solar zenith angle increase. MEMSCAG retrievals of grain size are insensitive to snow-covered area. The largest inferred grain sizes occur around a peak in the backward reflectance angles and the smallest generally occur at the largest view angles in the forward direction. Retrievals of albedo from MEMSCAG and Nolin/Dozier are similarly sensitive to anisotropy, with albedo errors up to 5% for a 30° solar zenith angle and up to 10% at 60°. The albedo differences between the two models are less than 0.015 for all grain sizes and solar zenith angles.
The effect of anisotropic reflectance on imaging spectroscopy of snow properties (full article)