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A Diurnal Reflectance Model Using Grass

Surface-Substrate Interaction and Inverse Solution

^a Western Ecology Division, NHEERL, U.S. Environmental Protection Agency, 200 SW 35th St., Corvallis, OR, 97333
^b Botany and Plant Pathology, Oregon State Univ., Corvallis, OR 97331-7306

View larger version (25K): [in this window] [in a new window]   Fig. 1. Seasonal and diurnal radiance in Landsat MSS7 waveband recorded nadir over BaSO4 plate in Corvallis, OR, and fitted to a fourth-order polynomial in the normalized local time, T. The normalization, which adjusted local time for varying sunrise and daylength, helped to collapse seasonal data to within an error band shown.

View larger version (24K): [in this window] [in a new window]   Fig. 2. Seasonal and diurnal radiance in four Landsat wavebands each fitted to observed radiance (data points not shown) over BaSO4 plate in Corvallis Oregon using a fourth-order polynomial in normalized local time T.

View larger version (28K): [in this window] [in a new window]   Fig. 3. An example of diurnal radiance in four Landsat wavebands recorded nadir over a patch of grass in March 1995 with naturally grown canopy code n1 and dry wt. of 229.3 gm–2. The radiance in each waveband is fitted to a cubic polynomial in normalized local time T (Table 1, Line 1).

View larger version (26K): [in this window] [in a new window]   Fig. 4. Diurnal reflectance in four Landsat wavebands showing examples of naturally grown grass canopy with top intact (code = n1), the top once clipped (c1), twice clipped (c2), and canopy fully harvested to the bare ground (cg). Canopy codes, dates and dry weights match the listings in Table 1.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Trajectories of diurnal canopy reflectance interactions in SR1 and SR2 obtained by using paired treatments of grass patches: two natural patches (n2n1), natural with clipped (n2c1, n1c2), two clipped (c1c2), and canopies in combination with bare ground (c2cg, n1cg, and n2cg) listing the differential weight (dw) in round numbers (Table 2). The triangular zone depicts increasing canopy x ground (left-to-right) interactions in the four bottom row trajectories, increasing canopy x canopy (bottom-to-top) interactions in the four trajectories on right side of the zone, and mixed interactions in the interior and diagonal side.

View larger version (14K): [in this window] [in a new window]   Fig. 6. The error of recovering modeled dry weight (i.e., self-prediction of dry weight difference) for the whole triangular region in Fig. 5 (solid regression line) and the mean for each trajectory (symbol) and standard deviation relative to the mean (vertical lines drawn through the symbol). Data points are linked with line numbers in the top part of Table 2. Trajectories nearest the solid line are associated with strong and joint diurnal reflectance of paired patches.

View larger version (21K): [in this window] [in a new window]   Fig. 7. Trajectories of diurnal canopy reflectance interactions obtained mainly by pairing natural canopies (7 of total 13 test dataset, bottom part of Table 2), four natural canopies paired with bare ground, and two with clipped canopies (n5c1, n4c1). The contrasting trajectories here and in Fig. 5 represent seasonal differences and dominance of natural-natural canopy treatments.

View larger version (16K): [in this window] [in a new window]   Fig. 8. The error of predicting dry weight of test dataset by using all trajectories in Fig. 7 (solid regression line) and the mean for each trajectory (symbol) and standard deviation relative to the mean (vertical lines drawn through the symbol). Data points are linked with line numbers in the bottom part of Table 2.