Effect of dew on canopy reflectance and temperature
1986
Pinter, P.J. Jr
The diurnal behavior of canopy reflectance and emittance was characterized for six spring wheat cultivars using two ground-based radiometers that had spectral bandpass characteristics similar to the multispectral scanner and thematic mapper radiometers on Landsats 4 and 5. Nadir measurements of spectral reflectance and emittance were made over well-watered canopies with and without dew to determine its effect on each wavelength interval. The diurnal patterns of reflectances from canopies without dew were symmetric with respect to solar noon. However, when dew was present on canopies, morning reflectances in wavelengths shorter than 0.7 μm and longer than 1.15 μm were significantly different than those observed during the afternoon under similar solar zenith angles. Quantitative measurements of dew density in each cultivar established that moderately high dew levels increased reflectance in visible wavelengths by 40–60%, and decreased reflectance in wavelengths between 1.15 and 2.35 μm by 25–60%. No effect of dew was noted in the near-IR region of the spectrum between 0.7 and 1.1 μm or the thermal IR (10.4–12.5 μm).
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