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Title: Inclusion of a simple vegetation layer in terrain temperature models for thermal infrared (IR) signature prediction
Authors: Balick, Lee K.
Scoggins, Randy K. (Randy Keith)
Link, Lewis E. (Lewis Edward), 1946-
Keywords: Infrared detectors
Terrain models (Analytical)
Publisher: Environmental Laboratory (U.S.)
Series/Report no.: Miscellaneous Paper;EL-81-4
Abstract: Abstract: Thermal infrared signatures of natural and cultural features are dynamic, varying with time and weather conditions. Prediction of thermal signatures for specific conditions requires first that the actual temperature of the features be determined; for vegetation canopies this involves the average temperatures of canopy components and for planar (nonvegetated) surfaces the temperature of the surf ace. Models have been developed to handle layered vegetation canopies and layered ground surfaces; however, efforts have only begun to formulate a comparable capability for intermediate conditions such as grass covered surfaces where both the terrain surface and vegetation influence the average surface temperature. This report presents a procedure, named VEGIE, that predicts the temperature of terrain surfaces which contain a simple layer of vegetation. VEGIE is designed as an interim procedure for immediate application in lieu of more sophisticated and theoretical treatments of this problem. Operational flexibility and simplicity are preserved by using VEGIE as a submodel to the Terrain Surface Temperature Model (TSTM) developed previously at the U. S. Army Engineer Waterways Experiment Station. The TSTM predicts the surface temperature of nonvegetated layer and planar features using material thermophysical properties and meteorological conditions. The frameworks of the TSTM and VEGIE are presented along with the strategy for their joint application to temperature predictions for simply vegetated surfaces. The sensitivity of the temperature predictions to the inputs required by VEGIE are examined to assist in determining the limits of its validity. A limited validation is presented using measured data for a site in West Germany. Results from VEGIE are also compared to the output of a more sophisticated (and complete) vegetation temperature model developed at the Colorado State University (CSU). These models are applied to a deciduous and a coniferous canopy where the CSU model is valid but VEGIE is not. VEGIE is applied to the problem of estimating thermal signatures for terrain surfaces with less than total foliage cover, the consequences of changes in foliage cover, differing emissivities for the soil and vegetation, and reflected sky radiation. The data and analyses presented herein demonstrate that the simplified treatment of energy budgets used in VEGIE provide realistic results for the situations that VEGIE was designed to handle. Under some conditions, when sun and view geometry are important or where canopies have large horizontal variations to outline a few, the results from VEGIE may be of limited value. VEGIE would appear to perform well in moderate environmental situations such as lawns, pastures, and rangelands.
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