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United States Department of Agriculture

Agricultural Research Service

Sail ( Scattering by Arbitrarily Inclined Leaves)

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Current Version

WinSail, Version 1.00.04 

Historical Background

SAIL, developed by Bunnik and Verhoef (1984), models the spectral directional reflectance of uniform homogeneous vegetation canopies. It represents an extension to an earlier model developed by Suits (1972) to allow for Scattering by Arbitrarily Inclined Leaves.   In 1983, SAIL was implemented as a computer model by Lynn Alexander, a NASA contracter (see Alexander, L. (1983), SAIL Canopy Model Fortran Software, NASA, contract number NAS 9-15800).  The Fortran SAIL model was later enhanced by Dr. Fred Huemmrich, Joint Center of Earth Systems Technology (JCET), University of Maryland Baltimore County.

The PC SAIL Model software was converted from Fortran to Basic by Dr. Moon Kim to calculate and display bi-directional spectral reflectance, and transmittance for a range of wavelengths for several different Leaf Area Indices (LAI).  The program is menu driven with default values provided for most parameters for ease of operation.  The Kim version of SAIL was written in Microsoft QuickBasic.  It runs on the MS-DOS operating system (in MS-DOS windows on Windows 95/98/NT/2000/XP operating systems).

This new version of the SAIL model, WinSAIL, was developed in June, 2003 at the USDA-ARS, Hydrology and Remote Sensing Laboratory, Beltsville, MD.  WinSAIL is Kim’s PC SAIL model, rewritten using Microsoft Visual Basic for use on the Win95/98/… family of operating systems. 

Model Overview

The implementation of the SAIL model presented here predicts the canopy reflectance at a number of different sensor view angles in a user-defined relative azimuth plane (i.e., in a given direction relative to that of the sun). The software also allows you to vary the solar zenith angle, the Leaf Area Index (the area of leaves per unit area of ground) and the reflectance and transmittance of the vegetation in four separate wavebands, as well as the reflectance of the soil substrate and the proportion of sky radiance in these bands. Finally, for advanced use, the software allows you to vary the leaf inclination angle distribution (i.e., the geometric structure of the vegetation canopy).

Additional Information about SAIL


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Last Modified: 11/29/2015
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